Incidence of Sudden Unexpected Death in Epilepsy

Posted on April 24, 2026 by dulcetware

Seizures are a common condition, experienced by around 10% of people in their lifetime, and while in some cases epileptic seizures may be the consequence of a particular brain insult, a significant proportion have an ongoing susceptibility to epilepsy, rather parsimoniously defined as having had at least two unprovoked epileptic seizures. The distinction between a single unprovoked seizure and epilepsy is somewhat moot, since around 40% of those who have such an event will have another within two years if left untreated.

Perhaps unhelpful, or harmful, would be a better description than moot. Seizures are not a trivial condition; quite apart from the shocking nature of the event and the restrictions that it imposes upon lifestyle, such as the legal entitlement to drive a car, they are associated with a small but real mortality risk. While this is more likely in those who have frequent seizures, those who have had a single seizure are not immune.

The mortality asociated with epilepsy is termed sudden unexpected death in epilepsy (SUDEP) and was defined originally by Nashef as:

“a sudden, unexpected, witnessed or unwitnessed, non-traumatic, and non-drowning death in an individual with epilepsy, occurring during benign circumstances, with or without evidence of a seizure, excluding documented status epilepticus, where postmortem examination does not reveal a cause of death.”

Note that SUDEP is not about experiencing a seizure in a dangerous environment in which to lose consciousness or control, or even necessarily due to having a seizure at the time of death, though this is generally assumed.

Individuals who have epilepsy are often young and otherwise well and so SUDEP is obviously an extremely emotive topic, both for sufferers and doctors. There are cases where neurologists have been sued for not trying hard enough to make their patients compliant with medication and not informing them of the risk of SUDEP.

But how do we inform them of the risk if we do not know? In developed countries the risk in studies varies from 0.35 to 9.3 /1000 patients with convulsive epilepsy per year – a thirty fold variation. Such a wildly varying estimates makes a meta-analysis proclaiming that they average out at 1.2/1000 practically useless.

It remains unclear if the inaccuracy of SUDEP risk is because of varying definition, underreporting, no post mortem to prove that there is no other cause, population differences or a combination of factors. The studies that have been conducted have usually been on an uncontrolled sample and retrospective.

As well as informing patients of the risk, if one understands the level of risk, one might ascertain risk factors and so be able to mitigate them by medical intervention or education.

Again the findings are inconsistent between studies and range from male sex, suffering generalised tonic clonic seizures and poor medical complaince to seizure frequency, young age of onset, sleeping alone or being on multiple antiepileptic drugs.

The topic of this journal club is a large cohort long term prospective study published last year in Seizure: European Journal of Epilepsy by Rongxin Li et al, Incidence and risk factors of sudden unexpected death in epilepsy in rural Northeast China.

They recorded Nashef’s definition of definite, probable and possible SUDEP in a prospective epidemiological cohort of patients with convulsive epilepsy, conducting face to face interviews for epilepsy with monthly assessments of a median of 7 years. They had 6513 patients who had had a median duration of epilepsy of 32 years. 855 were lost to follow up. This meant there was a total of around 44,000 patient years. All were treated with valproate or phenobarbitone, or additional AEDs prescribed by a specialist.

The headline finding was 64 SUDEP deaths, which gives an annual incidence of 1.4/1000.

Regarding risk factors, they found the following statistically significant risk factors on univariate cox regression:

  • Higher BMI p=0.0116
  • Earlier age at onset p = 0.001
  • Longer duration of epilepsy p = 0.007
  • Higher generalised seizure frequency in last month or last year p=0.001

There were in fact 9 times as many non SUDEP as SUDEP deaths in this cohort, so they could use these events as competing risks to reduce bias. Using multivariable competing risks regression on the factors that were significant on univariate analysis, they determined relative risks:

  • Obesity had relative risk 1.06 (95% confidence interval:1.02 to 1.11)
  • Later age of onset was a protective factor 
  • Increased seizure frequency in last month had relative risk 12.10 (95% CI 7.39-19.84)
  • Increased seizure frequency last year had relative risk 11.56 95% CI 1.59-83.92)

Comments

It is worth putting the 1.4/1000 figure, which closely matches the consensus metanalysis figure of 1.2/1000, in the context of overall risk, as many patients may not grasp their significance. The risk of accidental death in the UK is 20,000 per year. Out of 68 million, this gives 1 in 3000, or 0.3/1000. So the risk of having epilepsy is four times as great. For further comparison, patients often want brain scans as they are worried they might have a brain tumour. Its incidence in the general population (and likely also in the population of people with chronic episodic headache) is 20 per 100,000 per year, so 1 in 5000, or 0.2/1000.

Regarding life time risk, that of death by RTA is 1 in 100, but the lifetime risk of SUDEP in a patient with epilepsy has been estimated at 7-12%. (This seems quite high; if a patient has epilepsy for as long as 50 years, this is 1.2 * 50 = 6%.)

The criteria for probable SUDEP are as follows: a history of epilepsy in the patient; sudden and unexpected death while in a healthy state; death occurring within minutes; death occurring during normal activities in benign circumstances; and no definitive cause of death identified upon clinical examination.

The criteria for possible SUDEP are as follows: the presence of a competing cause of death; no other significant underlying disease; death occurring in water but without complete submersion of the individual; and death occurring in a normal environment without an autopsy.

But, having explained all this, the study ignored it and lumped all possible and probable cases with definite cases because they had no post mortem data or examinations at death. This is a real issue; in a previous study in Chalfont in 2013, 40% of the apparent SUDEP deaths were cardiovascular related and not epilepsy related. The death rate not from SUDEP in the study’s population was quite high, increasing the possibility of uncertainty over cause.

In addition, the study explained that there was no correlation with AED adherence, but they only asked at assessments. One would have to question if patients recruited in a single cohort followed every month for many years would be reliable in retrospectively reporting their compliance. Other studies have recorded AED drug levels at autopsy and have indeed found a correlation, as might be supposed.

While the study might overestimate risks somewhat because of lack of post-mortem data, the prospective data ascertainment would seem to give a reliable figure. Moreover, the monthly assessments could give good data on seizure frequency, which was found to be the major risk factor for SUDEP.

Finally, as the study points out, it was conducted in a single rural region of likely uniform population and ethnicity. This might be somewhat differnt from the population in other countries.

Conclusion

The study gives more confidence in citing the figure of around 1.2/1000 per year for the risk of SUDEP. Of particular interest was the major risk factor of increased seizure frequency; in clinical practice, if a patient reports increased generalised tonic clonic seizure frequency, they should be assessed as a matter of some urgency rather than waiting for routine follow up, which in the UK may be six months or a year.

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Endovascular Treatment of Cerebral Venous Sinus Thrombosis

Posted on December 4, 2024 by dulcetware

Introduction

Cerebral venous sinus thrombosis is blockage of one or a number of venous vessels, often called sinuses when they are large vessels, that drain blood from the brain. This results in back-pressure, oedema and ischaemia that develops rather gradually compared with an equivalent blockage of an artery.

When severe, the ischaemia can result in infarction, i.e. permanent damage to the brain tissue. The back-pressure may result in general raised intracranial pressure, which in turn causes other effects including local haemorrhage, headache resulting from stretching of the meninges and other structures, interference with autoregulation of cerebral blood flow and papilloedema which, if left unchecked, can leave lasting retinal damage.

It might immediately be inferred from these facts that venous stroke, i.e. brain infarction, presents differently from arterial stroke; it is generally more gradual in evolution, with a wider range of manifestations. It is also much more rare. All these factors make it considerably harder to diagnose.

Another difference between arterial and venous stroke is the pattern of focal neurological deficits stemming from differences in blood supply. The cerebral veins are typically central, draining both sides of the brain, so the deficits are correspondingly bilateral rather than contralateral.

The superior sagittal sinus runs posteriorly over the convexity of the hemispheres along the central sulcus (this is why neurosurgeons tend to “steer clear of the midline”) and joins with the straight sinus to split into the two transverse sinuses. These also receive drainage from the cerebellar hemispheres, brainstem and veins directly supplying some cranial nerves. The transverse sinuses run into the sigmoid sinuses which then leave the skull as the internal jugular veins. Thus, sagittal sinus thrombosis may result in unilateral or bilateral cortical hemisphere deficits or in seizures, while transverse sinus thrombosis is more likely to result in general obtundation. Sometimes one transverse sinus is much more dominant than the other, making even these paired structures potentially likely to result in bilateral deficits if thrombosed.

In parallel, the deeper structures of the hemispheres are drained by the inferior sagittal sinus running deep within the central sulcus. This joins the great vein of Galen to form the straight sinus. The great vein of Galen drains the diencephalon structures and internal capsule and thrombus here is again likely to result in obtundation and behaviour changes as well as potentially bilateral long tract signs.

Finally, the cavernous sinuses behind the eyes have a number of cranial nerves and the carotid arteries running within them. These drain posteriorly via the petrosal sinuses into the sigmoid sinuses.

In contrast to the evolution over hours of arterial thrombosis, the symptoms of venous thrombosis evolve over days and diagnosis is often delayed by several days as a result. A plain CT head will detect up to 2/3 of sinus thrombosis from the hyperdensity of the posterior sagittal sinus near the transverse sinuses. Subarachnoid and parenchymal haemorrhage is also common and may be picked up on CT.

A CT venogram is more than 80% sensitive in detecting venous thrombosis, but due to false positives of normal anatomy is less than 50% specific.

MRI head may only pick up venous thrombosis after several days; complex signal changes take place on T1 and T2 due to methaemoglobin changes over this time while oxyhaemoglobin changes over the first few hours have unpredictable timing. In general, gradient echo is the best sequence. Regarding ischaemic and infarction changes, venous stroke often spares the cortical rim due to oedema building up more in the deeper layer of the grey-white matter junction.

MR venography is a sensitive non invasive investigation specifically for venous thrombosis.

If diagnosis of venous sinus thrombosis is difficult, management is still more uncertain. The American Stroke Association recommends anticoagulation for around 3 months or until demonstrated recanalization, even if there is secondary haemorrhage, but this is based upon very flimsy evidence. A Berlin trial around 25 years ago using unfractionated heparin showed some benefit, while a small Dutch trial in 1999 did not, though those patients may have been less severely affected on average.

It seems an attractive proposition to engage in more direct treatment of a clot, mechanically removing it or giving anticoagulation/ thrombolysis where it is needed, with less risk of worsening haemorrhage in distal or remote brain tissues.

However, it would not be the first time that a treatment might sound reasonable and yet not be efficacious. The only randomised controlled study before 2020 on thrombectomy (mechanically removing a clot) was terminated for futility as it was clearly showing no advantage over standard systemic anticoagulation.

The Current Study

It was against this background that the current study, Endovascular Mechanical Thrombectomy and On-Site Chemical Thrombolysis for Severe Venous Sinus Thrombosis (Liao et al., 2020; nature Scientific Reports, 10:4937) was reported. They essentially reviewed their consecutive cases between 2005 and 2015. Of 30 cases (compare that with arterial stroke!), 16 remained stable or improved and so had conservative therapy while 14 deteriorated and had intervention.

This intervention consisted of a catheter inserted up the venous circulation, manual aspiration of thrombus under angiographic guidance and bathing the vein in a thrombolytic again via a catheter for around 24 hours.

They found that, despite being a more severely clinically (and radiologically) affected group of patients, the eventual outcome as measured by modified Rankin score ( the same score used for arterial stroke) was not significantly worse than in the group that stabilised spontaneously on heparin. Specifically, 75% of the conservative group had a score of zero deficit on discharge, compared with 64.3% in the intervention group (p=0.504). At three months, the conservative group had 87.5% with a score of 0-1 and the intervention group 85.7%. I saw no breakdown of no versus mild deficit at three months, but the 0-1 figures on discharge were almost identical at around 85%, so return of function was rapid. In fact, the 2 remaining non 0-1 score patients on intervention were dead, while 1 patient in the conservative group had a score of 4 and one had a score of 5.

The authors concluded that intervention was non-inferior and relatively safe (the two deaths were not directly related to the procedure – one had intracranial haemorrhage progression (possibly related to thrombolysis depending on where in the brain it was) and the other had a pulmonary embolus). One can presume that, since the intervention patients started off worse rather than being randomised, this argued in favour of intervention in such severely affected cases. As is obligatory in every discussion, they suggested further studies.

They also compared results with another study done at around the same time. This was the TO-ACT study which was actually prospective and randomised 67 patients to intervention vs anticoagulation. At 12 months 67% of the intervention group and 68% of the heparin group had a good modified Rankin score of 0-1. Mortality was 12% in the intervention group vs 3% in the heparin group (p=0.2) and symptomatic intracerebral haemorrhage was 3% in the intervention group and 9% in the heparin group. The conclusion was obviously that there was no better outcome. Note that the extra deaths form part of the overall Rankin figures so it is a fair comparison, a little like the haemorrhage data for intravenous thrombolysis in arterial stroke where some patients did worse but the majority did better. Nevertheless, if you tell a patient there is 12% mortality if you perform thrombectomy and 3% if you don’t, not many are going to want to go ahead even if you plead it is not statistically significant at p=0.2.

Study Appraisal

Some interesting facts came out of the demographic data. The range of time from onset to diagnosis in the stable patients was 2 to 13 days, with a median of 7 days – clearly it is banal to make a direct comparison with time course and management of arterial stroke.

Other than this, the numbers are far too small to draw any conclusions at all. We find ourselves drilling down to individual patients to account for the Rankin scores in the two groups.

The statistical conclusion can only be that there is no evidence to show that thrombectomy has a different outcome from heparin therapy. Time and again, we must remind ourselves, and the journal Nature it seems, that this does not equate to evidence for no difference. Once more, no evidence for a difference is not the same as evidence for no difference. The latter requires a power calculation and it should have been possible to predict from the 2012 study that one was going to require thousands of patients for that, not 15 in each arm. The 67 total patients in the other study was equally doomed; perhaps there would be an advantage apparent in enough patients, or in the severely affected patients.

As a case series, one can infer that the intervention in their centre was a reasonable treatment option. The patients did really quite well despite being in a serious and deteriorating clinical category. The numbers are too small to assess safety more definitively.

Given the duration of their study and the multiple centres of the TO-ACT study that was only able to recruit 67 cases, the sad conclusion is that, in this rare disease, we are never likely to have the benefit of a watertight randomised study investigating interventions in appropriate clinical subgroups.

It may be one of the many clinical conditions where we must rely on clinical judgement and experience in individual cases, with the reasonable inference that, if the patient is otherwise relentlessly deteriorating, mechanical thrombectomy, at least in experienced hands, may offer a reasonable balance of risk versus benefit.

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Inhaled Levodopa

Posted on March 24, 2023 by dulcetware

Introduction

Levodopa was the first main, and arguably still the best, treatment for Parkinson’s disease. Being similar in structure to tyrosine, it is absorbed through the gut by an amino acid transporter – its half life in the blood is short, namely 0.7 to 1.4 hours. This has advantages in terms of avoiding peripheral dopaminergic effects and dopa decarboxylase inhibitors further reduce this latter effect.

The fact that the clinical action of levodopa is far longer than its half life is presumably due to presynaptic storage and control of release as dopamine and so it is no wonder that, as the disease progresses and there is increasing loss of the remaining presynaptic terminals, PD control from oral levodopa becomes more brittle and the clinician resorts to frequent dosing, longer acting agonists, delayed release preparations and even continuous intrajejunal delivery.

This review article, Profile of inhaled levodopa and its potential in the treatment of Parkinson’s disease, describes a further new delivery method, namely inhaled levodopa. This avoids the variability of gastric emptying and competing with the amino acids of food for absorption.

CVT301 inhaled levodopa is a complex of molecules in a large low density porous particle that can aerosolise and avoid phagocytic destruction in the lungs. The particles are readily absorbed through the alveolar membranes. The Arcus inhaler works by delivering the particles in dry powder form and requires the patient only to breathe in rather than also to activate a pump.

Phase I study

In a Phase I study, following safety trials in animals, plasma levodopa concentrations rose within 10 minutes of inhalation (they also took oral carbidopa) by healthy volunteers.

Phase II Study

Ini this study, patients with Parkinson’s disease and significant off periods had a median T max (time to max concentration ) of 15 minutes vs 66 minutes for oral, and clinical improvement (finger tapping) within 5 minutes and lasting 90-100 minutes.

Side effect of cough occurred in 25% which often settled after initial dose and was described as mild. There was less dyskinesia giving 50 mg than for oral 100 mg – but the study did not quantify the relative benefits of finger tapping tasks, so perhaps the oral was simply a bigger dose with more benefit and more side effects.

There were no differences in lung function between oral and inhaled groups after 4 weeks.

Phase III Study

There was a 12 week double blind, placebo controlled study in 339 patients with motor fluctuations randomised to placebo, 35 mg dose and 50 mg dose. Chronic lung disease was a contraindication.

Mean change on motor UPDRS at 12 weeks from pre treatment versus 30 minutes after treatment was -9.83 versus -5.91 for placebo (p = 0.009). There was no reduction in off time according to patient diaries; 85% of subjects completed the study. There were side effects of cough (14.5% versus1.9% placebo), URTI (6.1% v 2.7%), nausea (5.3% v 2.7%), sputum discolouration (5.3% v 0%), and dyskinesia (3.5% v 0%). Only two subjects discontinued due to cough. No statistically significant differences in FEV1 or diffusion capacity of lungs were found (but is this evidence for no effect on the lungs rather than no evidence for effect?).

Long-term studies

In a longer term open label study of 408 subjects, the treatment arm used a mean of 2.3 doses a day. After dosings at four weeks into the study, they experienced a mean UPDRS III change of -5.7 at 10 min, -12.0 at 20 min, -15.5 at 30 min and -16.1 at 60 min at 4 weeks and at 60 weeks the equivalent changes were -5.0, -11.5, -15.3, -14.8.

In another study, FEV1 and diffusion of carbon monoxide were not statistically different (!). Dyskinesia was worse; 5.5% versus 3.1% in the group with standard of care. Two of I think 100 subjects discontinued due to cough.

In a study of other subjects having morning off, subjects getting 50 mg inhaled levodopa came on in 25 mins vs 35 on placebo, and an on event was 35% more likely than after placebo.

The C max of the higher strength (50 mg) is 500 ng/ml while 100 mg oral achieves 700-1000 ng/ml. As the authors comment, there are no head to head comparisons of inhaled versus oral.

The authors conclude that inhaled levodopa is an option for rescue therapy.

Journal Club discussion

The data demonstrate only biological efficacy, and it does seem fast acting. There are not data on the quantitative effect versus oral levodopa or even the speed of action versus oral levodopa, dispersible levodopa or subcutaneous apomorphine. There appears to be no carbidopa or benserazide, so patients are going to be needing to take oral levodopa at around the same time or at least have had a decent amount fairly recently.

On a google search in March 2023, the cost is $1223 for 60 capsules of what is stated to be 45 mg but I think this is equivalent to 35 mg in the study. This might seem about a 1 month supply but no – one dose is two capsules. Patients had an average of 2 doses a day and the company specifies a maximum of 5 doses a day or ten capsules which is $204 a day!

In comparison, oral levodopa is $13 for 90 100 mg tablets. The 100 mg appears to be up to double the strength of the higher strength inhaled, which we presume is 2 capsules. So the cost of inhaled levodopa is over 500x greater than standard treatment. It does seem almost provocative not to attempt a comparison with standard care so much cheaper. We can surmise that perhaps inhaled might work about 15 minutes more quickly. The magnitude of benefit is demonstrated biologically but there is no comparison with oral. Measurements were made when the patients were rendered off to maximise the benefit rather than in a real world scenario dealing with unpredictable sudden off. Would the plasma concentrations as little as half that of 100 mg of oral really rescue such patients?

Regarding safety there are one year data. No worsened lung function was demonstrated but this does not mean there is evidence of no side effects unless the study was powered and the type B error quantified. We have many examples of preliminary data not showing the dangers revealed subsequently on post- marketing surveillance.

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Revolution in acute ischaemic stroke care: a practical guide to mechanical thrombectomy

Posted on March 24, 2023 by dulcetware

Introduction

Stroke is the most common cause of disability in Western Countries, and its lifetime risk is up to 25%. While managing acute stroke patients in hyperacute stroke units is regarded as having benefits for short and long term outcome, specific therapeutic options are limited. The first major option for treatment of ischaemic stroke was intravenous thrombolysis, paralleling its previous development in acute myocardial infarction. However, while use in the latter indication was widespread in the 1990’s, it has only been widely for stroke in the last ten years. This is probably because of the narrower therapeutic window and the more severe consequences of haemorrhagic complications in the brain. In addition, its benefits are actually relatively modest. In randomised clinical trials on use within three hours (bearing in mind that in the first hour a stroke often spontaneously recovers – termed a TIA), using NICE data (June 2007) 15% of patients have an improved outcome, but with a brain haemorrhage risk of 7% greater, and a major haemorrhage rate actually considerably worsening the stroke (>= 4 points on the National Institute of Health Stroke Severity Scale) of 1.7% . When delivered between 3 and 4.5 hours after stroke onset the benefits were not even clearly significant.

So it is not surprising that there has been a move, just like in cardiology a decade or two earlier, away from intravenous thrombolysis and towards direct intra-arterial catheter treatment. This article discusses this new treatment and the ramifications for delivery of such a service.

The paper, Revolution in acute ischaemic stroke care: a practical guide to mechanical thrombectomy, summarises recent evidence in favour of this treatment and the infrastructure required to manage patients in this way.

The Procedure

While the first such devices were approved for use in 2004, technical developments and the improved expertise that comes with experience show in recent studies published since 2010 on new generation devices that they yield major improvements in outcome. The HERMES collaboration meta-analysis revealed that 46% of patients had a good outcome with functional independence (grades 0-2 on the Modified Rankin scale) compared with 26.5% on best medical treatment. Most of the patients in both groups received intravenous thrombolysis, since in most study protocols patients had iv thrombolysis before going on to have thrombectomy an hour or so later. Mortality and the risk of brain haemorrhage did not differ between the two groups. The benefit seemed still to be present in patients over 80, and still present when patients did not receive iv thrombolysis, though the numbers in this case were smaller. While the window for thrombectomy was within 6 hours, there may still be improved outcomes up to 7.3 hours after symptom onset, but in generation faster intervention leads to greater benefit.

The procedure involves a number of variations depending on the Neuroradiologist and the particular nature of the thrombus. It may be done under general anaesthesia or local anaesthesia and sedation with anaesthetic support. A large gauge catheter is directed to the internal carotid via a femoral puncture, and an intermediate catheter inside it is directed to the Circle of Willis. Then a microcatheter inside that serves as a guide wire to the actual clot. The microcatheter is then removed and a stent retriever is placed within the clot, and pulled back to draw the clot to the intermediate catheter. Suction is applied to this catheter to remove the clot entirely. Some techniques involve directly removing the clot by suction on the intermediate catheter. A balloon may be located on the distal end of the clot to prevent forward movement. When removing the clot reveals a tight lumen, there is the further option to perform angioplasty or stenting to open the vessel. The same can apply to a more proximal carotid stenosis occurring in tandem with the more distal thrombus.

Complications

The main complications are technical, including vessel perforation (1.6%), other symptomatic intrcranial haemorrhage (3-9%), subarachnoid haemorrhage (0.6 – 5%), arterial dissection (0.6 to 3.9%), or emboli distally (1-9%). In addition , there can be vasospasm or issues related to the puncture site. While the total incidence is 15%, not always is there any actual clinical adverse consequence.

  • While the time window for thrombectomy is wider than for intravenous treatment, there are other selection criteria that are more strict.
  • There should be a documented anterior circulation large vessel occlusion of the middle cerebral or carotid artery. (There is only limited evidence for efficacy in basilar occlusion.)
  • There should be good collateral cerebral circulation.
  • There should be relatively normal extracranial arterial anatomy from the technical viewpoint of passing the catheter.
  • There should be significant clinical deficit at the time of treatment, but this parallels the criteria for intravenous treatment and a large vessel occlusion with minimal clinical deficit nevertheless incurs a significant risk of clinical deterioration.
  • There should be a lack of extensive early ischaemic change on CT (according to ASPECTS score a threshold of 5). The role of more advanced imaging , eg CT perfusion to establish salvageable brain, is yet to be clarified.
  • Consideration should be given to pre-stroke functional status and the potential of benefit.
  • Patients should have had iv thrombolysis within 4.5 hours of symptom onset.
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Testing for COVID-19 Infection

Posted on November 22, 2021 by dulcetware

Accurate testing for SARS-CoV-2 infection, by which we mean testing with few false positives as well as few false negatives, is important not only for clinical management of individual cases but for epidemiological case tracing, limiting spread of infection and informing public health strategies. In the latter situations, tests that are rapid, cheap and easy to perform are particularly desirable.

Two main forms of testing for SARS-CoV-2 infection are in use.

  • Antigen testing, which includes the self administered immunochromatographic lateral flow test (LFT), detects viral coat material and is developed by raising a specific antibody against the antigen target. It therefore measures active production of the viral protein that constitutes the antigen. Developing such a test requires knowledge of how the viral behaves in the host and is reliant upon generating a sensitive and specific antibody to be used for the test.
  • Molecular tests, such as polymerase chain reaction (PCR), loop-mediated isothermal amplification (LAMP) and clustered regularly interspaced short palindromic repeats (CRISPR) tests amplify viral RNA material. These tests are potentially specific for different variant mutations of SARS-CoV-2. The gold standard test is considered to be lab based reverse transcription viral PCR (RTPCR). Rapid testing, such as the LAMP test, skips some of the time-consuming stages of formal PCR and therefore is useful for screening and epidemiology.

Many different studies have reported on the performance of different brands of rapid antigen and molecular test. This article discusses a Cochrane review of diagnostic test accuracy that collected data from 64 studies that investigated 16 different antigen tests and five different rapid molecular tests. In all there were 24087 samples. Of these, 7415 were found on the subsequent gold standard RTPCR test to be positive. No study actually included clinical diagnosis of infection as a standard or criterion of infection.

Antigen tests had a sensitivity in symptomatic cases of 72% (95% CI 63.7 to 79%). The sensitivity was higher in the first week of infection (78.3%) than in the second week (50%). The overall specificity was 99.6% (in both symptomatic and asymptomatic – obviously if symptomatic one wonders what they actually had if we are considering false positives.

Analysing a different way, the positive predictive value (PPV) in comparison was only 84-90% using the best sensitivity brands at 5% population prevalence and at 0.5% prevalence in asymptomatic people the PPV was only 11-28%!

Molecular tests had an average sensitivity of 73% (66.8 to 78.4%) and specificity was 97.2 to 99.7% depending on brand. In most trials the samples were collected in labs rather than in real life conditions. There are no data about symptoms.

For reference, WHO considers >80% sensitivity and >97% specificity an appropriate test as a replacement for a lab test.

The authors note that in low prevalence settings the dramatically reduced PPV value means that confirmatory tests may be required and that data are required for the settings in which tests are intended to be used as well as on user dependence (i.e self testing)

Journal Club Conclusions

Why the huge difference between positive predictive value and specificity?

Specificity = 1 minus false positive rate (FPR)

FPR = false positives/all negative cases (i.e. true negatives and false positives)

So high specificity means false positives is low compared to true negatives

PPV = true positives/all positive results (i.e. true positive and false positives

So high PPV means false positives low compared to true positives

The difference between specificity and PPV is essentially that sensitivity is in relation to the total number of actual cases while PPV is in relation to the total number of positive test results. PPV could be much worse than specificity if the true negatives much more common that true positives. This would happen if infection rates are very low in the population.

Is it disingenuous to quote specificity based on trials where infection rates were 31% when in the real world the infection rates are perhaps two orders of magnitude lower than that? If someone wanted to argue that they were being denied going to work, going to school or going on holiday based on a test where the predictive value was only 11-28%, would they have a good case? Is it worthless as a screening tool? If the policy is to go on to a molecular test if the result is positive, is this also invalid if the PPV of the molecular test is similarly low?

Clearly, the use of tests should be tailored to the information that can be provided. In an outbreak of high prevalence, one wants a sensitive test to pick up people who might have infection after contact tracing. One could have a specific screen and lab test only those negative to make completely sure. The priority is not to miss positive cases.

If medicolegally one wants to prove workers were not source of a case or outbreak, when the prevalence of infection is low, one may as well go straight to lab testing as there are too many false positives in such a situation.

In a situation where someone wants to question a positive result, it is not clear that rapid molecular testing is superior to antigen testing, and a lab based PCR may again be necessary. as specificity not clearly higher than some molecular tests.

There are also biological as well as statistical issues. For example, antigen tests may theoretically have false positives if the nature of the generated antibody to a viral coat antigen is not clear. If the trial was done in the summer time with no winter flu or coronavirus common colds in a setting where one in three subjects have COVID and none has any other type of infection, is the generated antibody really shown to be specific for SARS-CoV-2? The same may apply to demographic factors, such as expecting the test to have the same performance in children or in care homes as in a healthy adult test population.

On the other hand, a molecular test may correlate better with actual infectivity than a bit of residual RNA and therefore be more biologically useful for epidemiological control.

Finally, in extremely high prevalence trial populations where there is no actual clinical corroboration, the absolute reliance upon lab PCR as a gold standard may be of concern.

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Distinguishing Encephalitis from Encephalopathy

Posted on December 11, 2020 by dulcetware

encephalitis

Encephalitis may be defined as infection or inflammation of the brain substance, resulting typically in disturbed sensorium and perhaps seizures or focal neurological deficits and sometimes pyrexia. Encephalopathy in the other hand represents disturbed sensorium not due to an infective or inflammatory cerebral process and its causes range from toxins and drugs to metabolic upset, non cerebral sepsis, cerebral hypoperfusion and post-ictal states.

Distinguishing the two is important because considerable morbidity and mortality is associated with delayed treatment with appropriate antiviral, antibiotic or immune therapy for encephalitis and with delayed treatment of the various causes of other causes of encephalopathy.

The paper presented, “To what extent can clinical characteristics be used to distinguish encephalitis from encephalopathy of other causes? Results from a prospective observational study” by Else Quist-Paulsen et al., attempts to use clinical and rapidly available investigatory findings to distinguish the two conditions by a prospective observational study on 136 patients.

They identified candidate patients on the basis they had a lumbar puncture, and then excluded those with no evidence of encephalopathy. Their criteria for encephalitis were:

  • Pyrexia
  • Encephalopathy > 24 hours with no other cause identified and 2 of:
  • CSF WCC >=5 x 106/l
  • New onset seizures
  • New onset focal neurological findings
  • CT/MRI consistent with encephalitis
  • EEG consistent with encephalitis

The gold standard by which to gauge their test would surely be a definitive diagnosis but, as is commonly the case in clinically suspected encephalitis, such a diagnosis was only made in 10 of 19 patients. In some of the patients with non-encephalitis encephalopathy, the diagnosis was also vague, e.g. “aseptic meningitis” (which could be encephalitis), “epilepsy” (which could be autoimmune encephalitis), “headache/migraine”, “unspecified disorientation or coma”.

Subsequent analysis of specific features in the two groups then becomes somewhat difficult because the criteria themselves become the gold standard and because some specific features were in themselves their criteria. Interestingly, systemic features of infection such as raised blood white cells or CRP, argued against encephalitis because general sepsis was a common cause of encephalopathy. Nausea and personality change were more common in their encephalitis group.

They used ROC curves to look at the predictive value of these specific features and their combinations, but these were again based against their “testing variable”, their criteria, not on some objective gold standard. It would have been better to look at them only in the 10 diagnosed cases rather than all 19, but then the total number of cases would be even lower.

The diversity of diagnosis of their cases was interesting, especially that Lyme disease and TB were as common as VZV and more common than HSV. Only one of their cases had NMDA receptor antibodies, but we do not know that all the patients had this test and a full battery of other autoimmune antibody tests. Many might have been put in the encephalopathy with seizures category. Since encephalitis can be associated with meningism, some “aseptic meningitis” patients might have been viral but with negative testing, or even autoimmune with a migrainous headache and stiff neck.

The group felt that the study was very worthwhile but a more clear guide as to which cases of encephalitis warranted antimicrobial therapy  or immune therapy would be the clear goal. This would require clarity on the gold standard diagnosis and many more patients.

The Journal Club discussion on which this post is based was presented by Dr Aram Aslanyan, Specialist Registrar in Neurology at Queens Hospital, Romford, Essex.

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Making a Differential Diagnosis using a Clinical Database

Posted on November 20, 2020 by dulcetware

Background

A great deal of time is spent in medicine reading and writing case reports. Essentially, clinical features are listed and a diagnosis made. Excluding those cases that point to a novel means of treatment, a case report is often noteworthy simply because the diagnosis is rare, or because the clinical features were most un-likely to be associated with the diagnosis. This hardly seems a reliable method of archiving medical knowledge.

Much less time is spent on attempting a method of diagnosis that is more systematic than the recalling of case reports. One can see that if one did wish to move medical diagnosis into the information age, natural instinct would be to use an internet search engine to enter a list of clinical features and see what disease diagnoses were associated with these terms. Unfortunately, internet search engines concern themselves only with the popularity of search terms and because of the dominance of case reports such practice may be likely to throw up the least likely cause of those features, or that which is most “titillating” to those who most perform internet searches.

There have been attempts to provide a more balanced means of linking clinical features with diseases and hence making clinical diagnoses. Rare disease with a large number of different clinical features are least easily diagnosed by clinical experience or key investigations, and so the focus of these attempts has been on rare genetic diseases using ever-expanding databases such as Orphanet, Online Mendelian inheritance in Man (OMIM) and the London Dysmorphology Database and the Pictures of Standard Syndromes and Undiagnosed Malformations (POSSUM).

One method of searching for clinical features on these databases is simple text matching. A way of quantifying the match is the feature vector method, which calculates the mathematical overlap between the Query (the clinical features of the case) and the Disease (the clinical features of the disease). A vector of the query is calculated with dimensions for each feature and a value of 1 if present and 0 if absent. The same is done for the disease. The dot product of the two vectors is the strength of the match (a 1 for both query and disease will sway the two vectors in a common direction, and a 0 for both will leave their relationship unchanged, while a 0 and a 1 will make one move away from the other).

A potentially better quantification of matching is to take into account the different specificities of different clinical features. If a clinical feature is present in only a few diseases, its annotation (the linkage of a clinical feature to a disease) is more specific for that disease (in database terms this is called the information content (IC)) and so that linkage should have more weighting. The IC is simply the negative log of the frequency of the annotation. For example, AV block is a term that annotates 3 diseases in the 4813-disease OMIM database. The frequency is 3/4813. Loge of this is -7.38 and minus loge of this is 7.38. A much more general term will have many annotations and a much lower negative log, tending towards zero. The ICs of all the clinical features of the query can be summed or otherwise combined to provide an overall match.

The authors of the presented paper have described a further refinement of this method. This is called the Ontology Similarity Search (OSS). Instead of simply matching the text of terms, they fit clinical features into a standardised language within an ontological framework. This means that the features are related to one another in a hierarchy, with more general terms higher in the hierarchy and more specific subcategories of those general terms lower in the hierarchy. While “parent” terms obviously have many “child” terms, child terms can also belong to multiple parent terms. For example, optic atrophy could be a child of demyelinating disease and also a child of visual disturbance. Their ontology is called the Human Phenotype Ontology (HPO) and has around 9000 terms.

The advantage of using the ontology is that if a clinical feature of a case does not fit the clinical features of the disease, but shares a parent term with one of the features of the disease, instead of scoring a zero match, this scores as a match but less so than if the match was with the specific terms. The method specifically find the most informative common ancestor of the two different clinical features, and uses the IC of that term. Being a more general term, it will be a feature of more diseases and so have a lower IC. (In the database, ancestor terms are implicitly annotated when child terms are annotated.) The overall strength of match is the average of all the ICs – there will always be a IC for each feature, even if it is just that they are both a feature of “any disease”, which of course has an IC of zero and would bring down the average.

Summary of the Paper

The presented paper, Clinical Diagnostics in Human Genetics with Semantic Similarity Searches in Ontologies by Köhler et al. (Am J Hum Genet. 2009 Oct 9; 85(4): 457–464), describes a further refinement of the method using a statistical treatment. For a given disease, if random clinical features from the HPO were selected one would expect a lower OSS score than for a patient who actually had the disease. If the OSS for random features were repeated many times, a distribution would be created and so one could then look at the real patient OSS and determine a p-value on this distribution. If the real OSS was higher than 95% of the random OSS scores, the p-value would be lower than 0.05 and indicate a likely match. Furthermore, if the same features were compared with different diseases and their random OSS distributions, a ranking of the likelihood of diseases could be determined by ranking the corresponding p-values. They call this the OSS –PV.

Since they considered it too onerous to enter, within the framework of the terms of the HPO, the clinical features of real patients with known diseases, they used simulated patients. This was done for 44 diseases, where they created a “patient” having a disease with a selection of the clinical features of the disease weighted by how commonly those features were found in that disease. For each disease 100 patients were created, so if from the clinical literature a feature is found in 1% of cases with the disease, 1 of the 100 simulated patients would have that feature.

They added “noise” to the process by adding to the patients some random features that were not part of the disease, and “imprecision” to the process by replacing some features with their HPO parent terms.

Then they looked at the rank position of the true disease among all the 5000 or so database diseases found by the different methods. The closer the rank position to the true position (first!), the better the method performed.

Unsurprisingly, the performance of the feature vector method, as shown by box plots of rankings for all 44 diseases tested, was found to suffer when imprecise terms were used, because that was the point of using the ontological system. The OSS-PV method more modestly outperformed the raw OSS method when noise and imprecision were added.

As the authors point out, the OSS method potentially suffers from the fact that it only matches query terms with disease terms. If a disease also had many terms that did not match the query terms, surely the overall match would be less specific. This can be taken into account by performing a symmetrical similarity search, where the OSS is the average of the matches of the query to the disease and the matches of the disease to the query. However, they did not use this method in their presented data, only stating that when they used it the symmetrical OSS-PV still significantly outperformed the feature-vector method. They do not state that it still outperforms the symmetrical raw OSS.

Another point raised by the paper is that if one finds on a disease search that no disease fits the features with a p-value less than 0.05, exploration could be made of other clinical features, or child features of the entered clinical features that would have a higher information content and provide a more significant match. Going back and looking for a specific feature, or performing a specific investigation, would be an example of this.

Journal Discussion

As described in the introduction, any attempt to quantify and rationalise differential diagnosis should be lauded and this paper clearly describes progressive refinements of this process. It is almost negligent to have all the data available on thousands of diseases and not to use them because the unaided human mind simply cannot store so much information.

However, a number of further refinements and limitations present themselves.

First, the matching of terms is still semantic rather that systematic. While a knowledge-based approach, it nevertheless does not rely on understanding of disease pathophysiologies and pathognomonic features. Some clinical features that share a close parent may in fact best distinguish diseases rather than be considered loosely positively associated features. This may apply particularly in neurology where there is a more systematic approach. For example, upper motoneurone lesion and lower motoneurone lesion may be considered together and share a common parent in “motor neurone lesion”, but apart from the case of motoneurone disease, they split the differential diagnosis more than upper motoneurone lesion and no motor lesion at all. They are semantically similar but nosologically opposite. Horizontal supranuclear gaze palsy and vertical supranuclear gaze palsy may share a strong information content parent, but may be the feature that best separates Gaucher disease from Nieman Pick disease.

This leads to the second point. The frequency, or sensitivity, of a clinical feature in a disease is not considered, although ironically considered when creating the simulated patients with the 44 tested diseases. In large part this reflects the lack of clinical data in the databases themselves. It is regrettable that case reports are not combined into case series which contain information on the frequencies of occurrence of clinical features, or when there are case series, these data are not actually collected systematically. If a clinical feature occurs in 1% of cases of one disease and 100% of cases of another disease, clearly the annotation of the feature for the second disease should be considered far stronger than for the first. Instead, because there are no such data, they are given equal weight; the weighting only considers whether or not the feature is also found in a number of other diseases, not how commonly it is found in those diseases.

There is no consideration of how common the disease is in the first place. While restricting themselves to rare and genetic diseases by definition, there can be a frustrating tendency for searches to throw up the least likely diagnosis. It is often the case in practice that the clinician does not know in advance that the patient has a rare genetic disease, and a diagnostic tool should be most useful to those with least intimate knowledge of the database. Thus, when entering the features dystonia, spastic hemiparesis and spastic dysarthria in a case of cerebral palsy, it comes as a surprise when the top diagnosis is cleft palate-lateral synechia syndrome.

Finally, the methods assume that clinical features are independent. In fact, many clinical features are strongly interdependent; they especially occur together. The association of the second feature is not really very additionally informative if the first is present. This problem would be common to most forms of differential diagnosis calculators, including those using Baysian methods, and could only be solved if there were data on the interdependence of clinical features in different diseases; currently it is hard to find even raw frequency data for most diseases.

The point that the authors raise about using their App to find features that would be more specific in making a diagnosis is an interesting one, and opens a new approach to diagnosis and refinement of the process of often expensive and sometimes risk-associated investigation. One could imagine the improvements in medical care that would arise from use of an App that gave a differential diagnosis based on initial clinical information and then showed the relative power of different investigations in narrowing that differential.

A further use of these methods would be in creating diagnostic criteria. While clinical practice is rightly focused on the most likely diagnosis in a patient, clinical research is focused on a group of patients where the diagnosis is certain, i.e. specificity at the expense of sensitivity. Currently, diagnostic criteria seem to be set largely by “workshops” – gatherings of the great and the good usually in an exotic location who draw up a list of features, create two categories of importance and then decide how many features are required for a “definite diagnosis”. Using a quantified method such as that described in this paper for every study patient and including only patients where the diagnosis reaches a threshold p-value score would seem to be a far more reliable method.

The paper on which this journal club article is based was presented by Dr John McAuley, Consultant and Honorary Senior Lecturer in Neurology at Queens Hospital, Romford.

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Coronavirus

Posted on March 6, 2020 by dulcetware

Coronavirus is obviously not a neurological disease, apart from an isolated case report of encephalitis associated with the condition, which is to be expected very rarely in association with viral infections, but because it is so topical this paper Clinical Characterisics of Coronavirus Disease 2019 in China, published in haste in the New England Journal of Medicine on 3rd March, 2020, was nevertheless presented.

Background

A novel enveloped RNA virus of coronavirus type, similar to SARS coronavirus, was first identified as causing viral pneumonia in early December 2019 and named as Covid-19 disease. It is believed to have first been transmitted through livestock in a large market in Wuhan, Hubei province. It is thought in general that such viruses are endemic in wildlife, such as in bats, and mutate to become transmissible to other animals and to humans.

As of Friday 6th March, there were 100,645 confirmed cases worldwide, and 3411 deaths linked to the virus. There were 55,753 cases who had recovered. In Hubei province, for the first day since the outbreak no new cases had been reported.

The details are unclear, but the fact that the UK government is said to be moving from a containment to a delay phase suggests that at least some UK cases have been identified that appear to have had no contact with potential suffers in China, Iran, Italy or other hotspots, nor with other UK individuals known to have the disease.

Journal Club Article

The paper discussed is an early report focusing on numbers affected, initial outcomes and clinical presentation. It was approved by the Chinese authorities.

Data were sourced from records of laboratory confirmed cases using assay of nasal and pharyngeal swabs between 11th December 2019 and 29th January 2020. Certain hospitals were sampled, so by no means were data collected from all cases.  In all, 14.2% of all known hospitalised cases were included in the study. It is not clear how widespread was the screening of the population by these laboratory tests; all the patients in this study were hospitalised.

26% of these cases had not had contact with Wuhan residents, indicating widespread serial human to human transmission.

Clinical information is as follows:

  • Incubation period (presumably from ascertaining likely time of exposure was median 4 days (2 to 7 days interquartile).
  • Fever in only 44% on admission, but developed later.
  • Cough in 68%.
  • Viraemic symptoms occurred in some patients, but upper respiratory tract symptoms, lymphadenopathy and rash were very rare.
  • CT chest abnormalities were very common (86%) in both mild and severe cases.
  • Lymphopaenia was common (83%).
  • Only 1% of cases were under 15 years old.

Of these hospitalised cases, 926 were considered mild and 173 severe. The main factors predicting this were advanced age and comorbid disease (especially coronary heart disease, diabetes, COPD and hypertension), also breathlessness at 38% versus 15% (unsurprisingly as this would be a criterion for severity). Similarly, inflammatory markers and markers of multi-organ involvement were associated with more severe disease. The main complicating feature of severe cases was acute respiratory distress syndrome, occurring in 16%.

The outcomes were 25% risk in severe cases of intensive care admission, mechanical ventilation or death (8%). Only 0.1% of cases categorised as non-severe died. The overall death rate was 1.4%. The national statistics at the time had a death rate of 3.2%.

By the data cut-off point, 95% of mild cases and 89% of severe cases were still hospitalised; the median lengths of hospital stay were 11 and 13 days respectively. Perhaps mild cases were hospitalised for purposes of isolation.

Journal Club Discussion

The paper reports likely ascertainment bias from milder cases not being tested. Nevertheless, the scale of the morbidity and mortality of the disease is not underestimated. Ascertainment bias becomes more relevant if one expects a pandemic and most of the population to become exposed. By these means the population risk can be inferred.

The paper also reports the fact that many patients were still in hospital, and perhaps very unwell, by the study’s end point. In the study, the number of cases requiring intensive care treatment is three times the death rate. Perhaps the death rate of already infected cases may climb. On the other hand, ARDS, the major serious complication of coronavirus infection, has a mortality of around 40%, and since 16% had this condition and 8% died, perhaps few more would be expected to die.

There does appear to be an opportunity for more information to be gleaned from these data or similar studies. The large number of cases could be randomised to have treatments not clear to be effective, such as oseltamivir, steroids and intravenous immunoglobulin. Less than half of cases had these treatments, but nevertheless appreciable numbers. It would have been helpful to know the death rates for patients who did or did not have these treatments rather than only the end point rates, as in reality some of these treatments might be most relevant when patients have already reached the ITU admission end point.

A follow up study would give better indicators of important epidemiological issues such as ultimate death rates and morbidity, the possibility of reinfection versus lasting immunity and any signs that more recently infected cases, where transmission has been via several human hosts, have any milder disease than those directly exposed to the transmitting animals.

A population based study that tested all individuals in high risk areas would determine the likely proportion of individuals who have been infected but not become very symptomatic.

Worldwide, we would also want to know how ambient temperature and sunlight levels affect transmissibility.

One suspects that epidemiologists in charge of advising governments have more information than is released to the public, and various advanced tools to model infection spread, but from the recent explosion of cases in Italy and now elsewhere, where talk is of delay rather than containment, there is little confidence that the slowing up of cases in China is going to be replicated worldwide.

From the death rates reported in Italy, there appears to be no clear evidence that the disease is becoming milder, but from the delay of many days from exposure to developing critical illness, perhaps it is too early to tell.

The lack of cases in hot or southern hemisphere countries would suggest a seasonal effect of the virus, and some reassurance to northern hemisphere countries approaching Spring. But in Australia there were already 40 cases confirmed by 4th  March and at least three cases had had no recent foreign travel and no traceable contact.

It seems that one scenario for the UK is that the infection eventually replicates that of Hubei province, which has a similar population to the UK and had around 11,000 cases with few new cases to come, and with around a 1-3% mortality rate, mainly in the elderly and infirm for whom ‘flu’ is also a significant source of mortality. With around 20% of cases classed as severe, this would require an extra 2000 of some form of high dependency inpatient beds for several days and spread over only a month or two.

However, we do not have an explanation for the slowing of new infection rates in China. It could be that most of the local population has already been exposed and most were resistant to severe symptoms, or it could be that containment measures have been very effective. If the latter is the explanation and is in reality only delaying inevitable spread through the population, or if containment is not replicated to the same degree in Western countries and if there is no seasonal dip in transmission, one could imagine hundreds of thousands of cases in the UK spread over the next year. And with a current mortality rate seemingly up to 3% this is unlikely to drop when there are insufficient hospital resources to manage such numbers.

The paper on which this journal club article is based was presented by Dr Bina Patel, Specialist Registrar in Neurology at Queens Hospital, Romford.

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Anticonvulsant Medications for Status Epilepticus

Posted on December 9, 2019 by dulcetware

Status epilepticus is a medical emergency with significant morbidity and mortality and, in circumstances where benzodiazepines alone have failed to terminate seizures, has traditionally been treated with anticonvulsants such as phenytoin or phenobarbitone. Other intravenously administered antiepileptics have also been found to be effective.

There is a lack of comparative data on different anticonvulsants and this blinded prospective study “Randomised Trial of Three Anticonvulsant Medications for Status Epilepticus” by Kapur et al. (2019) compares three options: fosphenytoin (a pro drug of phenytoin which is more expensive but more soluble and can be given intravenously faster with fewer extravasation problems and can also be given intramuscularly), valproate and levetiracetam.

Study Details

Patients in the study had to be over 2 years of age, and had to have convulsive status (persistent or recurrent convulsions) for at least 5 minutes, and then more convulsions between 5-30 minutes after an adequate dose of benzodiazepine (5 minutes to have allowed the benzodiazepines to work and less than 30 minutes, after which point another dose of benzodiazepines could have been tried instead). Patients were randomised by stratifying for age.

Patients with major trauma or anoxia, etc., were excluded, as were pregnant women (give levetiracetam and consider magnesium).

The doses of the intravenous anticonvulsants levetiracetam (60 mg/kg) and valproate (40 mg/kg) seemed very high.

The primary successful outcome was absence of clinical seizure activity and improved responsiveness at 60 min after infusion start.

Analysis was based on assuming equal prior probability of success for the three treatments, then using the binomial probability of positive or negative outcome to calculate the posterior probabilities. An iterative method was then used from these three separate probabilities to calculate the probability that a given treatment was better than the other two, or worse than the other two.

The sample size was set on the basis of correctly identifying with 90% probability a difference when one treatment was 15% better than the other two (65% response for the best and 50% response for the other two).

A total of 400 patients were enrolled. The intention to treat population was only 384 because some patients were enrolled more than once. Nearly a third of patients were then excluded because treatment did not follow the protocol, e.g. not status epilepticus such as functional seizures, did not receive the correct amount of benzodiazepine or anticonvulsant or wrong timing with respect to benzodiazepine.

Half the patients were unblinded to avoid suboptimal management.

In the per-protocol population, 47% of patients responded to each of the three treatments, with probability of most effective treatment distributed as follows: levetiracetam (0.34), fosphenytoin (0.35), valproate (0.31). There was also an “adjudicated population” outcome, which was perhaps based on an adjudicator clinician looking retrospectively at the notes, whether following the protocol or having had previous treatment or not, and deciding if the treatment worked. Although the data were similar, it did seem that levetiracetam may have been worse (0.51 versus 0.29 and 0.2) and clearly 0.51 is 31% worse than 0.2 (valproate), which is more than their threshold of meaningful difference of 15% for best treatment.

Secondary outcomes included requirement for admission to ICU (87% for levetiracetam and only 71% for valproate).

Regarding safety, there were 4.7% deaths in the levetiracetam group and 1.6% in the valproate group, with fosphenytoin in the middle. Hypotension, a known issue with phenytoin was 3.2% in the fosphenytion group to a life-threatening degree and only 0.7% for levetiractem and 1.6% for valproate. Cardiac arrhythmia only occurred in one patient. Acute respiratory depression occurred in 12.8 % with fosphenytoin and 8% with levetiracetam and valproate. None of these differences reached significance.

The conclusion was that there was no difference between the drugs.

Journal Club Discussion

The study was welcome as it was on an important practical topic. The group wondered about the high doses used, and whether our own guidelines should reflect these doses. The trial was powered for the primary efficacy outcome and then stopped. However it was always going to be as likely that any differences between the drugs wold lie in their side effects as in their efficacy and it is a shame that the powering did not reflect this so that what may have been real differences in respiratory depression or hypotension never reached significance.

The vagaries of statistics are illustrated by the per-protocol efficacies, which seem identical, and the adjudicator population efficacies, where there was actually a 31% greater chance of levetiracetam being the worst drug compared to valproate.

Negative study results always make us turn to how the study was powered: were there no differences seen because there are no differences, or because too few patients were studied (i.e. too low power)? When powering a study, a judgement must always be made on what level of difference would be considered meaningful, otherwise if accepting any difference as being meaningful it would require an infinite population to prove there is no difference. They chose a meaningful 15% difference for one drug being better than the other two, but if they had chosen one drug worse than the other two, the 31% difference in the adjudicator population would have been more than their set level. There should have been more explanation of their adjudicator population, and perhaps more explanation of the advantage of using Baysian probabilities in addition to a simple comparison of means and standard errors of success rates.

In real practice, there should perhaps be tailoring of treatment to the patient. If a patient is already on therapeutic levels of phenytoin, is more of the same going to be the best choice? If a patient is a female of child bearing potential, is valproate the best choice when the patient often ends up on the oral equivalent of the status treatment they received. On reviewing the data in this study and knowing that the levetiracetam dose was very high, valproate might shade the other two choices, especially in men.

The Journal Club on which this article is based was presented by Dr Katie Yoganathan, SpR in Neurology at Queens Hospital, Romford.

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Galcanezumab in Chronic Migraine

Posted on November 8, 2019 by dulcetware

Migraine is one of the most common neurological conditions, and chronic migraine is a condition that, while less common than episodic migraine, is nevertheless a major cause of loss of quality of life in otherwise well individuals.

Once analgesia headache has been effectively treated, and tension type headache excluded, chronic migraine is treated with migraine preventative medications, often very effectively. However there are a proportion of patients who remain resistant to single or combination preventative treatments.

A novel target for migraine treatment is the calcitonin gene related peptide CGRP receptor on the smooth muscle of blood vessels in the head. CGRP is released from trigeminal ganglion efferents to the blood vessels to cause potent vasodilation as part of the trigeminovascular response (analogous to the “triple response” of pain, redness and swelling of skin inflammation). Blocking this may therefore block this response. Monoclonal antibodies raised against the receptor, or against CGRP itself, have been explored as migraine treatments.

This study describes a double blind trial on galcanesumab, one such monoclonal antibody targeting CGRP. The paper does not discuss the relative hypothetical or actual benefits versus other monoclonal Ab migraine therapies already marketed or in development.

Study Design

Around 270 patients were given each of two doses of galcanezumab by monthly subcutaneous injection, and 560 were given normal saline placebo. To be enrolled on the study, patients had to have 15+ headache days per month, at least 8 of which had to be migraine days. They needed at least 1 headache free day per month. If a patient failed >3 other preventatives, they were excluded. Before the study, patients had to stop all their existing migraine preventatives except propranolol or topiramate at least 30 days before study start.

Migraine days were defined as >30 minutes of migraine or probable migraine according to ICHD-3 beta criteria (even though the duration criterion of the latter is 4+ hours). If a patient thought it was a migraine and it did not satisfy the criteria but responded to a triptan, that also counted as a migraine day.

Over 90% of patients completed the study. Only 15% of patients were on topiramate or propranolol (not specified if this was the same proportion in the three treatment groups).

The primary outcome measure was migraine days per month. At the start of treatment, this was around 19 days. Placebo reduced this by 2.7 days per month, low dose galcanezumab by 4.8 days and high dose by 4.6 days. Therefore, compared to placebo, the drug on average reduced migraine by 2 days per month. There were only about 2 extra non migraine headache days per month on average.

There were many secondary measures. Of note, 4.5% of placebo patients had a 75% reduction in migraine days, and 7% of low dose and 8.8% of high dose patients, while 0.5% of placebo patients had a 100% response, and 0.7% of low dose and 1.3 % of high dose patients (not significantly different).

There was no overall quality of life measure, but there was a migraine related quality of life measure that showed significantly more improvement, about 25% more improvement than placebo. There was a patient global disease severity 7 point scale, where there was a 0.6 point improvement from placebo, and 0.8 for low dose and 0.9 for high dose, only the latter reaching significance.

The side effect profiles were similar between placebo and drug, notably common in both groups! However, there were no concerning side effects, nor indeed any characteristic enough to tend to unblind the patients or investigators.

Opinion

The Journal Club thought it was strange that the study would exclude the very patients in whom the drug would mainly be used, namely those who had failed >3 conventional treatments. The focus was clearly on maximising benefit as measured by the study. By the same token, patients had to stop any preventatives before the study, even if they were partially beneficial, apart from topiramate and propranolol.

It was furthermore strange that only 15% of the recruited patients were on the two most common treatments for chronic migraine. Had they only been tried on the others, or had they had side effects? In real practice, there are usually at least some marginal benefits from preventatives and patients often remain on them.

It is therefore possible that many patients were treatment naïve as far as preventatives were concerned. This makes the 2 fewer migraine days per month vs placebo (from an initial 19 days per month) an all the more modest magnitude of benefit.

It is difficult to reconcile the cost of the drug with the fact that patients on average will still have 15 migraine days a month. Most patients would not consider this a treatment success, and certainly not such that a patient would happily be discharged from specialist care. In terms of patients having a 75%+ reduction in migraine days, generally the minimum level of meaningful benefit in a pain study, the excess over placebo was only 3-4% of patients.

The lack of a general quality of life measure means that cost benefit analysis cannot be performed. The quality of life measure used was specific for migraine and likely to show much larger differences; a cured migraine sufferer might have a near 0% to 100% swing on this scale, but another individual considering the range from death to total disability to perfect health might assign curing migraine only a swing from 90% to 100%.

A major aspect of migraine care is what happens when treatment is stopped. Patients do not want lifelong medication, let alone lifelong monthly injections. Fortunately we find that after six months of treatment, traditional preventatives can often be withdrawn. Although the study mentioned that there was an open label period and then a wash out period, we do not know any of these results; presumably they are to be held back for another publication. Is there rebound migraine on treatment withdrawal? Any funding body would want to know if the patients would likely need the treatment for 3-6 months or for many years.

As a final point, it was queried whether the definition of migraine is sufficiently specific; perhaps this limits the observed benefit in this and similar studies. Some headaches recorded as migraine may be tension type headache and therefore not responsive to specific anti-migraine treatment. The table below shows the relevant criteria.

ICHD-3 Headache Diagnostic Criteria

Probable Migraine Probable Tension Type Headache Definite Tension Type headache
2+ of: 2+ of: All of:
4-72 hours duration 30 min to 7 days duration 30 min to 7 days duration
2+ of:

Unilateral,

Pulsing,

Moderate+ severity,

Avoid routine physical activity

 2+ of:

Bilateral

Pressing or tightening

Moderate- severity

Not aggravated by routine activity

 2+ of:

Bilateral

Pressing or tightening

Moderate- severity

Not aggravated by routine activity
Nausea or

Photo plus phonophobia

 No nausea

Not both phono and photophobia

 No nausea

Not both phono and photophobia

 

A headache is diagnosed as a migraine if fits probable migraine and is not a better fit with another headache diagnosis, which presumably means definite rather than probable tension type headache. The severities and durations overlap so they cannot distinguish. One of photophobia or phonophobia overlaps. So a unilateral, pressing headache with avoidance of routine activity with no nausea no photophobia and no phonophobia  is classified as migraine as long as it lasts 4 hours, but it seemed that some of the migraine days were half an hour of headache. Also a headache not satisfying these criteria is a migraine if there is a response to triptans, but we have seen the large placebo response already from the main data. In general practice a tension type headache might be unilateral, and might interfere with routine activity if at the more severe end of the scale; certainly a neck ache or jaw (including temporalis muscle) ache from which a tension headache may arise may have these features.

The paper on which this Journal Club article is based was presented by Dr Piriyankan Ananthavarathan, Specialist Registrar in Neurology at Barking, Havering and Redbridge University Hospitals Trust.

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