Functional neurological disorder and somatic symptom disorder in Parkinson's disease

The occurrence of Functional Neurological Disorder (FND) and Somatic Symptom Disorder (SSD) in PD was not commonly accepted until recently, despite some evidence that emerged in the pre and early L-Dopa era. More recently, the recognition of FND and SSD were noted to be relevant for the management of PD. FND and SSD appear early in the course of PD, often preceding motor symptoms, may interfere with treatment outcomes, often acquire psychotic features during progression, and are mixed with and often concealed by the progressive cognitive decline. We review the related features from the range of the available reports and discuss theoretical models conceived to explain the potential pathophysiological background of these disorders. Finally, we suggest that FND and SSD should be included among the non-motor symptoms of PD and be considered a prodromal feature in a subset of patients.This article is part of the Special Issue Parkinsonism across the spectrum of movement disorders and beyond edited by Joseph Jankovic, Daniel D. Truong and Matteo Bologna.

Automated summary

The presence of FND and SSD in PD is significant for its management. These disorders may manifest early in PD, interfere with treatment outcomes, and be accompanied by cognitive decline. This article reviews their features and discusses their potential pathophysiology, suggesting that they should be included among the non-motor symptoms of PD.