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Functional neurological disorders in Parkinson disease
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  • Published on:
    Reply to “The eye of the beholder and risks of eminence based medicine”
    • Anthony E. Lang, Movement Disorders Neurologist University of Toronto
    • Other Contributors:
      • Benjamin D. Wissel, Medical Student
      • Alberto J Espay, Movement Disorders Neurologist

    We appreciate Dr. Laura S. Boylan’s interest in our article. However, her viewpoint rather strikingly exemplifies the behaviors that she mistakenly believes we were guilty of in our report, beginning with the “eminence based” statements “in my view” occurring twice in the first paragraph and her conclusion with a personal “old saw I use in teaching”. We strongly disagree with her misinterpretation about our application of “cognitive bias” in the selection of our patients for this case-control study. In fact, most patients with Parkinson’s disease (PD) had functional complications ascertained after several visits –requiring a diagnostic revision once they fulfilled the appropriate positive criteria.1 The diagnostic “delay” in part may have highlighted the absent recognition of functional comorbidities in PD prior to our study, forcing a conservative approach before ascertaining what may be considered a “second” diagnosis in these patients. Furthermore, in contrast to Dr. Boylan’s suggestion, we did not select patients on the basis of comorbid depression, anxiety, cognitive symptoms, pain, nausea, or fatigue. Instead these features segregated more commonly among cases than controls after the patient selection had been completed. She argues that we considered them “supportive” for a diagnosis of functional movement disorder, but we did not. We have instead emphasized the potentially misleading influence of both history and psychiatric features and argued in favor of a diagnos...

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    Conflict of Interest:
    None declared.
  • Published on:
    The eye of the beholder and risks of eminence based medicine

    In my view the data presented in this study (1) which are interpreted as indicating a high prevalence of functional movement disorders (FMD) in PD might also be interpreted as suggesting that diagnostic delay is common in PD, particularly among women patients who present as "high maintenance" patients. The diagnosis of functional movement disorders is a matter of expert opinion and in my view problems with study design and interpretation support rather than minimize cognitive and confirmation bias in this study.
    Subjects all met UK brain bank criteria for PD. Subjects diagnosed with FND in this study had high rates of family history of PD. They had depression, anxiety, cognitive symptoms, pain, nausea, fatigue all common complaints among the population in general and most particularly in PD. The presence of these symptoms before or after diagnosis of PD is considered by the authors as supportive for a diagnosis of FMD. However, these same symptoms are known to be associated with PD and might be considered supportive of a PD diagnosis.
    Disparities in healthcare for women are well established (2). Neurology has a long history of mistakes distinguishing the "functional" from the "organic" (e.g.3). To choose one example people with blepharospasm, mostly women, were institutionalized long-term as the disease was not recognized as neurologic. Women commonly encounter dismissal in the medical context and this can occasion missed opportuni...

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    Conflict of Interest:
    None declared.
  • Published on:
    Degeneration of the locus coeruleus in premotor Parkinson's disease could predispose to functional neurological disorders
    • Stoyan Popkirov, Neurologist University Hospital Knappschaftskrankenhaus Bochum, Germany

    Wissel and colleagues recently reported on a large retrospective case series of patients with functional neurological disorder (FND) and Parkinson's disease (PD) [1]. The authors only briefly touched upon the question of shared pathophysiology, noting that in principle certain structural brain diseases may predispose to FND. The study was not designed to tease out any shared or causal pathways between FND and PD, but some speculation based on the presented data could help formulate useful hypotheses concerning this interesting comorbidity. I propose that a disruption of the central noradrenergic system due to degeneration of the locus loeruleus (LC), the sole source of noradrenaline in the brain with far-reaching projections, is a good candidate for a causal link between FND and (prodromal) PD.
    In the study by Wissel and colleagues FND antedated the diagnosis of PD in 26% of cases, often by several years [1]. This is significant, because it nearly eliminates the possibility that the comorbidity is entirely a matter of symptom modelling or functional overlay in all cases. Considering the typical neuroanatomical progression of Lewy pathology in PD, this suggests that neurodegenerative effects within the lower brainstem (Braak stage 1 or 2) are likely structural candidates for a causal pathway. Early LC pathology has been associated with other premotor manifestations of Lewy pathology and PD such as REM sleep behaviour disorder and cognitive decline. A study using...

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    Conflict of Interest:
    None declared.