Objective: To describe changes in phenotypes of Functional Movement Disorders (FMD) over time and identify associated clinical and demographic variables.

Background: Like other functional neurological disorders (FND), patients with FMD are predisposed to developing functional symptoms throughout life, which may be reflected in phenotype changes over time.

Method: We performed a retrospective chart review (2011–2024) of FMD patients in a tertiary movement disorders clinic. We considered the initial phenotype reported by patients and that observed by specialists at the first and subsequent assessments, according to FMD classifications [1]. Only patients with continued follow-up were included.

Results: Of 105 patients followed for a median of 21 (7.4–51.5) months, 80% were female, with a mean age at onset of 44.5 ± 18.9 years. The most frequent phenotypes at the first assessment were mixed (23%), tremor (13%), and dystonia (12%), with a median onset-to-consultation time of 22 (10-48) months.

Before the first assessment, 37 (35%) patients had changed their initial phenotype, primarily from tremor, gait, and dystonia to mixed phenotypes, over a median of 24 (8-102) months. In 71% of these cases, the initial phenotype persisted while additional phenotypes emerged, indicating a tendency to accumulate phenotypes over time. During follow-up, 18 (17%) patients changed phenotype, mostly to mixed and gait, in a median of 8 (2.75-12.5) months [figure 1].

Patients who did not modify the phenotype (NMP, n=58) were more likely to have a poorly defined initial phenotype (19% vs 2%) than patients who did modify the phenotype (MP, n=47), who had more well-defined initial phenotypes, but were less stable over time (p < 0.05). Additionally, MP patients showed more changes in phenotype characteristics (i.e., pattern) (47% vs 26%), constant FMD (47% vs 29%), fatigue (45% vs 24%)  and sensory symptoms (32% vs 19%) than NMP (p < 0.05). Multivariate analysis indicated that an initial tremor phenotype, adjusted for changes in phenotype characteristics and sensory symptoms, could predict future phenotype modification [table 1].

Conclusion: Patients with FMD are prone to changes in phenotype and to adding multiple phenotypes over time. Initial FMD phenotype, variability in phenotype characteristics, and some non-motor symptoms were associated with future modification in phenotype. These findings highlight the complexity of FMD and the need for continued follow-up.

Figure 1

Table 1

References: 1. Lidstone SC, Costa-Parke M, Robinson EJ, Ercoli T, Stone J; FMD GAP Study Group. Functional movement disorder gender, age and phenotype study: a systematic review and individual patient meta-analysis of 4905 cases. J Neurol Neurosurg Psychiatry. 2022;93(6):609-616. doi: 10.1136/jnnp-2021-328462.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/changes-in-functional-movement-disorders-fmd-phenotype-a-retrospective-study/