eLetters

612 e-Letters

  • Guillain-Barré syndrome in developing countries in the COVID-19 era

    Dear sir,

    Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become one of the most severe pandemic the world has ever seen. Based on data from Johns Hopkins University, around 26.3 million cases have been detected and around 0.9 million patients have died of COVID-19 globally as of September 04, 2020. The neurological sequelae of COVID-19 include a para/post-infectious, immune or antibody-mediated phenomenon, which classically manifests as Guillain-Barré syndrome (GBS).[1, 2]

    We read the systematic review by Uncini et al with great interest. In an instant systematic review, the authors reported 42 patients of GBS associated with COVID-19 from 33 retrieved articles. All of these articles had been reported from 13 developed countries.[3] The authors mentioned regarding the chronology of publication of case reports/series starting from China followed by Iran, France, Italy, Spain and USA which seemed to be related to the track of SARS-CoV-2 infection spread. However, the authors did not discuss why such cases/series had remained under-reported from developing countries. A comprehensive, advanced search of PubMed using the terms ‘SARS-CoV-2’ OR ‘COVID-19’ AND ‘Guillain-Barré syndrome’ on September 04, 2020, led to retrieval of two additional articles from developing countries, one each from Brazil and Morocco.[4 ,5] As of September 04, 2020, Brazil and India had the 2nd and 3rd highest number of COVI...

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  • Response to Kemp et al.

    We read with interest Kemp and colleagues response to our recent systematic review on Performance Validity Testing (PVT). In response to specific criticisms raised:

    1- The searches and data extraction were conducted by one investigator. We agree this is a potential limitation although only if papers were missed, or data was erroneously transcribed, and it can be demonstrated this would have changed the conclusions. Although Kemp and colleagues place great weight on this, the evidence they put forward to support their contention was limited. Of the four citations in their letter, reference 2 and reference 4 were in fact included (see our supplementary tables and our reference 57)(1,2). Reference 3 was, by coincidence, published simultaneously with our manuscript submission and was not available to us(3).

    Reference 1 did not fit the terms of our search strategy and was not included although it would have been eligible(4). It was an unblinded study of the ‘coin in hand test’, a brief forced choice screening test for symptom exaggeration, administered to 45 patients with mixed dementias. It found 11% scored at or above a 2 error cut off and the authors proposed a new set of cut offs for interpretation; it was in keeping with our conclusions. We’d be happy to consider any other specific omissions or quality assessment issues not discussed which the authors consider would have altered the conclusions of the review.

    2- The authors criticise our understanding...

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  • Migraine and risk of stroke: complexities of population-based studies that do allow emergence of migraine science from the shadows of the past 100 years.

    I read the review by Øie et al. on the possible link between migraine and stroke (1). The authors believe that migraineurs are more likely to have unfavourable vascular risk factors. The increased risk of stroke seems to be more apparent among migraineurs without traditional risk factors (1). The mechanism behind the migraine- stroke association is unknown and clinical implications are uncertain (1).

    While migraine and stroke are independently common disorders, the occurrence of migraine-related stroke, in particular ischemic stroke in migraine with aura (MA), is uncommon to rare. Risk of ischaemic stroke associated with migraine without aura (MO) is uncertain (1). MO is by far the larger cohort (~80%), and, the striking absence of link of MO with ischemic stroke (1) merits greater attention. Additionally, as underscored by the authors, longer cumulative exposure to MA, as would be expected with early onset of migraine, is not associated with increased stroke risk in late life (1), an unexplained clinical paradox. The link between migraine and stroke is extremely tenuous and needs a careful re-examination. The authors (1) make no attempt to clarify that, fundamentally, no pathophysiologic difference between MA and MO has been established, and, both cohorts believed to be nosologically distinct respond equally well to abortive and preventive management strategies. What is truly challenging is the scientific basis and logic of the entirely arbitrary creation of noso...

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  • Response to Commentary by Prof. Gupta: Hemiplegic migraine, genetic mutations, and cortical spreading depression: a presumed pathophysiologic nexus that defies scientific logic

    We read with interest the commentary from Prof Gupta (1). Migraine is a complex and heterogeneous disorder with multifactorial pathogenesis (2). In fact, it is a well-known fact that both genetic and environmental factors are involved in the etiopathogenesis of migraine (2). Conversely, hemiplegic migraine (HM) is a complex monogenic disorder related to a mutation in genes encoding for ion transporters (3). Even if many consider HM as a subtype of migraine, this condition offers insight in migraine pathophysiology, especially in the case of migraine with aura, as well as in other conditions overlapping between headache and epilepsy, such as the so called “Ictal Epileptic Headache”, a new concept defined in the last decade (4–6).
    Our knowledge on the pathophysiology of both migraine and HM is evolving with new insights coming from the last years (3). However, we partially agree that ….“No systemic influence can explain the characteristic lateralizing headache of migraine, unilateral, bilateral, side-shifting or side-locked” (7,8). Interestingly, new data have come from neurophysiology: hyperexcitability/dysexcitability (5) in migraine has been clearly demonstrated in migraine sufferers with more prominent results especially in migraine with aura (5,9,10). These data could make a reasonable link between the genesis of hyperexcitability/dysexcitability of multisensory cortices, cortical spreading depression (CSD) and the “headache” phase of migraine, mediated by the tri...

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  • Letter: Response to McWhirter et al (2020)

    McWhirter et al. (2020) reviewed the published literature on Performance Validity Tests (PVTs), concluding that high false positive (Fp) rates were common in clinical (non-forensic) samples, exceeding 25%. In their discussion, they stated: “The poor quality of the PVT evidence base examined here, with a lack of blinding to diagnosis and potential for selection bias, is in itself a key finding of the review.” They also conclude that the use of a forced choice format with cut scores that are significantly above chance on two alternative forced choice tests (e.g., TOMM), raises questions about the utility of the forced choice paradigm, essentially characterizing these PVTs as “floor effect” procedures. As such, McWhirter et al. then argued that failure at above chance cutoffs represents “functional attentional deficit in people with symptoms of any sort,” rather than invalid test performance due to intent to fail.

    Throughout the paper, the authors refer to PVTs as “effort tests”, a characterization that is no longer in use in the United States, in part because PVTs require little effort to perform for persons experiencing significant cognitive impairment (1). Rather, PVTs have been defined as representing invalid performance that is not an accurate representation of actual ability. Continuing to refer to PVTs as “effort tests” allows McWhirter et al. to more easily mischaracterize the tests as sensitive attentional tasks affected by variable “effort” rather than measur...

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  • Response to McWhirter et al

    Dear Editor

    Response to McWhirter et al (2020):

    In their article, Performance validity test failure in clinical populations - a systematic review, McWhirter and colleagues (2020) present the ‘base rates’ of performance validity test (PVT) failure (or what are commonly referred to as effort tests) and offer an analysis of PVT performance from their perspective as neurologists and neuropsychiatrists.

    As a group of senior practicing clinical neuropsychologists, we are pleased that they have drawn attention to an important issue, but we have significant concerns about the methodology used and with several of the conclusions drawn within the review. We present this response from the perspective of U.K. neuropsychology practice, and as practitioners involved in research and formulating clinical guidance on the use of PVTs. In preparing this response, we were aware of parallel concerns of our U.S. counterparts (Larrabee et al) but we have submitted separate responses due to the word limit.

    The systematic review methodology used by McWhirter et al. has resulted in a limited number of papers being included, and there is no indication of the quality of the studies included. All of the literature search and analytic procedures appear to have been undertaken by one person alone, hence there was no apparent control for human error, bias, omission or inaccurate data extraction. Also, it is unclear to us to what extent McWhirter and colleagues had the knowle...

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  • Answer to response of professor Kawada

    Our findings demonstrate that serum C-reactive protein (CRP) does not predict survival in amyotrophic lateral sclerosis (ALS), neither in a univariate model nor in a multivariate model including other established prognostic factors for survival in ALS. In contrast, in a similar multivariate model, serum neurofilament light chain (NfL) is an independent predictor of survival in ALS. Further, we investigated the combination of serum CRP and NfL within the same multivariate survival model. The results indicated that elevated levels of serum NfL (Hazard ratio: 1.83 [95% CI: 1.23-2.74] p = 0.003), but not of serum CRP (Hazard ratio: 0.93 [95% CI = 0.63-1.37], p = 0.7), are associated with a shorter survival in ALS. From these data, we can conclude that there is no evidence that combining both markers would improve the prediction of survival in ALS.

    Moreover, we determined the disease progression rate (DPR) at time of sampling for 368 patients with ALS. The DPR was calculated as (48 – ALS-FRS-R)/(disease duration). We found a significant correlation between the DPR and serum NfL levels (rs = 0.519 [95% CI = 0.437-0.592], p < 0.0001) as well as serum CRP levels (rs = 0.294 [95% CI = 0.194-0.387], p < 0.0001). Accordingly, patients with a DPR in the upper quartile had significantly elevated levels of serum NfL (median [range]: 183 [11.1-738] pg/mL vs. 67.9 [0.300-262] pg/mL, p < 0.0001) and serum CRP (median [range]: 0.336 [0.0150-30.0] mg/dL vs. 0.0775 [0.0150-2.7...

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  • Brain Atrophy is Inevitable Following Deep Brain Stimulation and Not Likely Caused by the Lead

    Brain Atrophy is Inevitable Following Deep Brain Stimulation and Not Likely Caused by the Lead

    To the Editor,

    We read the observational DBS cohort study by Kern DS et al with great interest. We agree that deep brain stimulation (DBS) implantation has been associated with brain atrophy. We previously published an experience that not cited in the present study and we wonder whether the authors accidentally cited one of our review articles rather than the primary source (2014). It is critical for the DBS field to be aware of the clinical implications of atrophy.

    Kern DS et al analyzed 32 Parkinson’s disease (PD) patients who completed bilateral staged DBS implant surgeries targeting the subthalamic nucleus (STN)(1). The patients had an average duration between the two DBS surgeries of 141 days and this duration offered an opportunity to compare pre-post atrophy measures. The authors observed a significant reduction in whole brain volumes of the ipsilateral or first implanted side. Also, the authors noted that all basal ganglia-thalamocortical brain regions (BGTC) ipsilateral to the DBS implantation had significantly reduced volumes, whereas non-BGTC structures seemed to be unaffected. The authors suggested the possibility that intracranial volumetric changes may occur following STN DBS electrode implantation as a direct result of the implantation itself.

    We believe it unlikely that DBS electrode implantation is a primary reason for volume loss. We...

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  • Hemiplegic migraine, genetic mutations, and cortical spreading depression: a presumed pathophysiologic nexus that defies scientific logic

    I read the article by Stefano et al with interest.1 Genetic predisposition per se cannot explain discrete self-limited recurrent attacks of headache and aura manifestations of hemiplegic migraine, with the state/clinical predisposition appearing and disappearing seemingly inexplicably over several decades or the life-time of a sufferer.2

    More than two decades ago, I elucidated a fundamental clinico-theoretical principle for the understanding of migraine-linked physiologic mechanisms that has well-stood the test of time, technology and biologic commonsense: “No systemic influence can explain the characteristic lateralizing headache of migraine, unilateral, bilateral, side-shifting or side-locked”.3 Over the last fifty years, some of the "systemic" influences believed to play key pathogenetic roles in migraine include serotonin, platelets, catecholamines, calcitonin-gene related peptide, magnesium depletion, stress, post-stress state, and recurrent micro thrombo-embolisms across the patent foramen ovale at the level of the cardiac inter-atrial septum. 4,5,6 Little vertical and biologically-plausible robust generalizable progress, however, has been made in gestalt understanding of the disorder well into the 21st century.7 Trait-linked genetic association is also a “systemic” influence. Ion transporters – as well as the three main causative genes—CACNA1A, ATP1A2 and SCN1A—which encode for ion transporters1 do not offer clues to the mechanistic physiological b...

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  • Mechanisms of ischaemic stroke in COVID-19: more data are needed

    Dear Editor,

    We thank Dr Venketasubramanian for their interest in our paper and for their considered response. We agree that some of our patients had alternative causes for stroke in addition to the marked prothrombotic and inflammatory state related to COVID-19, and that this point is relevant to interpreting our findings.

    We also agree that it can be difficult to define one specific “cause” for an ischaemic stroke despite detailed investigation, since many patients have a complex combination of risk factors (e.g. diabetes, hypertension, dyslipidaemia), disease processes (e.g. atherosclerosis, cerebral small vessel disease, atrial fibrillation), and potential mechanisms (e.g. large artery thrombo-embolism, cardiac embolism, small vessel occlusion). Nevertheless, our key observation was that a 16-day period we saw 6 strikingly similar patients, all with large vessel occlusions, elevated D-dimer, ferritin and CRP, 8-24 days following proven COVID-19 illness (and in one patient during the asymptomatic phase (1), suggesting the emergence of a distinct pattern of cerebral ischaemia associated with a prothrombotic inflammatory state.

    As correctly identified, Patient 2 had atrial fibrillation and previous mitral valve repair (not a metallic valve), but stroke occurred despite above-therapeutic anticoagulation with INR 3.6; this is unusual, so we concluded that the clear thrombotic state may therefore have been contributory (D-dimer 7,750). Similarly, al...

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