Objective: This following review aims to clarify the link between functional and organic parkinsonism, in order to improve the understanding of functional symptoms in PD.

Background: Parkinson’s disease (PD) and functional neurological disorders are common neurological disorders, usually considered as distinct and non-overlapping. However, recent studies showed that functional symptoms and PD co-occur in 1.4 to 7 % of patients with PD [1], [2]. Accurate diagnosis of PD with functional neurological disorder is critical, since functional symptoms in PD may lead to significant disability, escalation of anti-parkinsonian treatment, request for alternative therapy such as deep brain stimulation, and poorer quality of life [2]. Moreover, correct identification of functional symptoms in PD might improve the knowledge about pathophysiology and potential common mechanisms involved in both diseases [3].

Method: Following the PRISMA guidelines, we performed a systematic literature search using the PubMed database and Science Direct until December 2018, to identify studies of patients suffering from either functional parkinsonism or Parkinson’s disease associated with functional symptoms.

Results: From the 844 articles screened, we retained 22 studies including 12 about functional neurological symptoms in PD, and 16 about functional parkinsonism. Functional symptoms in PD studies examined a total of 121 patients including 69 women (57%) with a mean age of 61.3-year-old. Psychiatric history (mostly depression) and exposure to triggering stressors were frequent: 60 and 80.5% respectively. The most common symptom was tremor (n=42, 34.7%), most often located on the most PD-affected side as (50 % (n=38)). Studies about functional parkinsonism examined a total of 120 patients with 62.1% women and a mean age of 50.7 year-old. Half of these patients had the first prodromal symptoms about 5 years earlier, and half had an acute onset. 68% had a psychiatric history and 46.8% were exposed to triggering stressors, such as physical injury, stress at work, and/or loss of family/friends.

Conclusion: This review shows a strong relationship between PD and functional parkinsonism, and highlights the importance to search for functional symptoms.

References: [1] M. Onofrj et al., « Updates on Somatoform Disorders (SFMD) in Parkinson’s Disease and Dementia with Lewy Bodies and discussion of phenomenology », J. Neurol. Sci., vol. 310, no 1‑2, p. 166‑171, nov. 2011. [2] B. D. Wissel et al., « Functional neurological disorders in Parkinson disease », J. Neurol. Neurosurg. Psychiatry, vol. 89, no 6, p. 566‑571, june 2018. [3] I. Pareés et al., « Functional (psychogenic) symptoms in Parkinson’s disease: Functional Symptoms in Parkinson’s Disease », Mov. Disord., vol. 28, no 12, p. 1622‑1627, oct. 2013.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/functional-motor-symptoms-in-parkinsons-disease-and-functional-parkinsonism-a-systematic-review/