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Objective: Functional motor disorders (FMDs) are disabling neurological conditions characterized by abnormal movements which are inconsistent and incongruent with recognized neurological diseases. Aim of this study is to investigate whether FMDs are related to structural axonal damage., Methods: Consecutive patients with a definite diagnosis of FMD with no other neurological/psychiatric comorbidities (pure FMDs) and age-matched healthy controls (HCs) were recruited in a tertiary center and demographic/clinical data were collected. Serum neurofilament light chain (NfL) assessment was performed with ultrasensitive paramagnetic bead-based enzyme-linked immunosorbent assay., Results: 34 patients with FMDs and 34 HCs were included. NfL levels were similar (p = 0.135) in FMDs (median 8.3 pg/mL, range 2-33.7) and HCs (median 6.1 pg/mL, range 2.7-15.6). The area under curve (0.606, 95% CI 0.468-0.743) confirmed that NfL concentration was not different in the two groups. NfL values were similar in patients with paroxysmal vs persistent disease course (p = 0.301), and isolated vs combined symptoms (p = 0.537). NfL levels were associated with age (p < 0.0001), but not with disease duration (p = 0.425), number of CNS acting drugs (p = 0.850), or clinical features (p = 0.983)., Discussion: Our preliminary data show that NfL levels are similar in patients with FMDs and HCs, indicating the lack of neuroaxonal damage. These results have relevant pathogenic and clinical implications and suggest that serum NfL may be a promising diagnostic biomarker, potentially useful to differentiate functional vs structural neurological disorders., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany.)

Introduction: Functional motor disorders (FMDs) are usually categorized according to the predominant phenomenology; however, it is unclear whether this phenotypic classification mirrors the underlying pathophysiologic mechanisms., Objective: To compare the characteristics of patients with different FMDs phenotypes and without co-morbid neurological disorders, aiming to answer the question of whether they represent different expressions of the same disorder or reflect distinct entities., Methods: Consecutive outpatients with a clinically definite diagnosis of FMDs were included in the Italian registry of functional motor disorders (IRFMD), a multicenter data collection platform gathering several clinical and demographic variables. To the aim of the current work, data of patients with isolated FMDs were extracted., Results: A total of 176 patients were included: 58 with weakness, 40 with tremor, 38 with dystonia, 23 with jerks/facial FMDs, and 17 with gait disorders. Patients with tremor and gait disorders were older than the others. Patients with functional weakness had more commonly an acute onset (87.9%) than patients with tremor and gait disorders, a shorter time lag from symptoms onset and FMDs diagnosis (2.9 ± 3.5 years) than patients with dystonia, and had more frequently associated functional sensory symptoms (51.7%) than patients with tremor, dystonia and gait disorders. Patients with dystonia complained more often of associated pain (47.4%) than patients with tremor. No other differences were noted between groups in terms of other variables including associated functional neurological symptoms, psychiatric comorbidities, and predisposing or precipitating factors., Conclusions: Our data support the evidence of a large overlap between FMD phenotypes., (© 2021. The Author(s).)