Objective: To characterize the etiological spectrum of hemidystonia in a case series and reassess its association with structural basal ganglia lesions.

Background: Hemidystonia is a clinical syndrome defined by dystonia affecting one side of the body and traditionally attributed to contralateral basal ganglia lesions. However, reports describe cases associated with lesions at multiple levels of the neuraxis despite structurally intact basal ganglia on neuroimaging. In addition, non-lesional isolated forms have been reported.

Method: Patients with hemidystonia evaluated between 2023 and 2026 were identified from Movement Disorders Clinics of two hospitals in the Community of Madrid, Spain. Clinical data were collected retrospectively. All patients underwent 1.5T brain MRI. When a genetic etiology was suspected, next-generation sequencing was performed.

Results: Eleven patients were included (63.6% female). Mean age at dystonia onset was 32.7 years (range 0–66) and mean disease duration 30.8 years (range 2.4–66.1). Eight patients (72.7%) had structural lesions attributed to vascular insults (36.4%), perinatal injury (27.3%), or undetermined causes (9.1%), most frequently involving the thalamus (45.5%) and putamen (45.5%). Three patients (27.3%) had no explanatory lesions on neuroimaging; one had a presumed genetic etiology and two were classified as idiopathic. Two patients underwent genetic testing, one harboring a microduplication at 14q11.2 associated with neurodevelopmental abnormalities.

Conclusion: Hemidystonia in this series showed heterogeneous etiologies including structural, genetic, and idiopathic forms. Basal ganglia lesions were not universally present, challenging the traditional view of hemidystonia as an exclusively lesional disorder. These findings support hemidystonia as a clinically recognizable but etiologically diverse syndrome that may arise from distinct, and possibly convergent, pathophysiological mechanisms.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/hemidystonia-beyond-the-basal-ganglia-etiological-heterogeneity-in-an-11-patient-case-series/