Diverse paths of phenotypic evolution in functional movement disorders: A longitudinal perspective.

Introduction: Functional Movement Disorders (FMD) exhibit a variable course over time. Understanding FMD phenotype trajectories may improve knowledge of its natural history and prognosis.

Methods: Retrospective study of FMD patients seen at a tertiary movement disorders clinic (2011-2024). Motor symptoms before the first consultation T(-1), FMD phenotype at first consultation T(0), and FMD phenotype at last consultation T(1), were considered. We compared the clinical and demographic characteristics of patients who modified the phenotype from T(0)→T(1) versus those who did not.

Results: Among 112 patients (81.2 % female, mean age at onset 46.0 ± 18.8 years), the most common FMD phenotypes were mixed, tremor, and dystonia, with a median time from onset to T(0) of 15 (8-48) months, and follow-up of 21.7 (7.9-54.8) months. Motor symptoms at T(-1) were mainly tremor and gait disorders. One-third of patients had changed the motor symptoms from T(-1)→T(0), mostly to mixed forms. From T(0)→T(1), 13.2 % of patients displayed a change in the phenotype, mainly from dystonia, tremor, and parkinsonism to mixed FMD. Family dysfunction, variability within the same phenotype, change in location, and worse patient-reported status were more frequent in patients with phenotype modification. Logistic multivariable analysis showed that functional dystonia at T(0), adjusted for within-phenotype movement variability, predicted phenotype modification.

Conclusions: FMD patients often showed changes in phenotype over time, tending toward more mixed forms. Certain clinical features may help predict these changes, emphasizing the importance of continued follow-up.