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

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

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.

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.

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.