Objective: To describe clinical and demographic characteristics of a Spanish cohort with Parkinson’s Disease (PD) and Functional Movement Disorder (FMD) comorbidity.

Background: Functional overlay in PD patients is not uncommon but studies specifically investigating characteristics of functional motor comorbidity in PD are sparse [1,2]. PD with FMD has been associated with greater psychiatric disability and an excessive use of diagnostic and therapeutic resources [2], emphasizing the need for a correct diagnosis.

Method: We used a standardized form to extract clinical and demographic data from subjects with PD and FMD (PD-FMD) from five Movement Disorders Units in Spain. Patients were matched for age, gender and disease duration with a control group of PD-only patients. Bivariable analysis were performed to compare groups using R software (3.6.2 version). Significance was set at p < 0.05.

Results: A total of 28 patients with PD-FMD were included (68% females, mean age 59.1±13.3 years, mean PD duration 7.8±6.1 years). FMD preceded/co-occurred with PD in 25% of patients. A precipitating event was reported in 36% (mostly physical). Functional tremor was the most common FMD (29%), followed by gait disorder (21%) and parkinsonism (21%). FMD involved the most affected PD side in most cases. PD-FMD patients displayed more non-motor symptoms (p<0.01), especially depression, anxiety, sleep disorders and cognitive complaints. However, dementia prevalence did not differ between groups. Compared to controls, PD-FMD had higher unemployment rate (75% vs. 38%; p=0.03), but similar UPDRS-MDS III score (p=0.44) and H&Y stage. In the PD-FMD group, the levodopa equivalent daily dose (LEDD) at the time of FMD diagnosis was higher than in the controls (PD-FMD LEDD=745±408 mg, PD-only LEDD= 459±328 mg; p=0.02) and decreased by up to 20% after diagnosis.

Conclusion: In our cohort, PD-FMD was more prevalent in females, in contrast to known PD male predominance. Similar to previous reports, functional tremor was the most common FMD and FMD was frequently ipsilateral to PD [2]. PD-FMD subjects had similar motor scores than controls, but displayed higher unemployment rates, likely due to higher non-motor symptom burden or FMD itself. The difference in LEDD between groups suggests that the correct identification of FMD comorbidity can prevent iatrogenesis. Our study is limited by the small sample size and retrospective data collection.

References: [1] Pareés I, Saifee TA, Kojovic M, et al. Functional (psychogenic) symptoms in Parkinson’s disease. Mov Disord. 2013;28(12):1622-1627. doi:10.1002/mds.25544
[2] Wissel BD, Dwivedi AK, Merola A, et al. Functional neurological disorders in Parkinson disease. J Neurol Neurosurg Psychiatry. 2018;89(6):566-571. doi:10.1136/jnnp-2017-317378

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MDS Abstracts - https://www.mdsabstracts.org/abstract/functional-movement-disorder-comorbidity-in-parkinsons-disease-a-multicenter-descriptive-study-in-spain/