Functional motor disorders associated with other neurological diseases: Beyond the boundaries of "organic" neurology

Objective: 1) to describe the clinical manifestations of functional motor disorders (FMDs) coexisting with other neurological diseases ("comorbid-FMDs"); 2) to compare comorbid-FMDs to FMDs not overlapping with other neurological diseases ("pure FMDs"). Methods: For this multicenter observational study, we enrolled outpatients with a definite diagnosis of FMDs attending 25 tertiary movement disorders centers in Italy. Each subject with FMDs underwent a detailed clinical assessment including screening for other associated neurological conditions. Groups comparisons (comorbid-FMDs versus pure-FMDs) were performed in order to compare demographical and clinical variables. Logistic regression models were created to estimate adjusted odds ratio (OR; 95% confidence interval) of comorbid-FMDs (dependent variable) in relation to sociodemographic and clinical characteristics (independent variables). Results: Out of 410 FMDs, 21.7% (n=89) of patients had comorbid-FMDs. The most frequent coexisting neurological diseases were migraine, cerebrovascular disease and parkinsonism. In the majority of cases (86.5%) FMDs appeared after the diagnosis of neurological disease. Patients with comorbid-FMDs were older, had more frequent tremor, non-neurological comorbidities, paroxysmal non-epileptic seizures, major depressive disorders, and benzodiazepine intake. Multivariate regression analysis showed that diagnosis of comorbid-FMDs was more likely associated with longer time lag to reach the final diagnosis of FMDs, presence of tremor and non-neurological comorbidities. Conclusions: Our findings highlight the need of a prompt diagnosis of FMDs, given their relatively high frequency of associated neurological and non-neurological diseases.