Adult-onset Idiopathic Focal Lower Extremity Dystonia: A Rare Task-Specific Dystonia

BACKGROUND: Adult-onset focal lower extremity (LE) dystonia is rare, but there have recently been a number of case series that have reported an idiopathic variant triggered during ambulation. METHODS: We describe nine patients with idiopathic, focal task-specific LE dystonia. We conducted a comparative analysis that included our cohort and several recently published case series to further characterize the disorder. RESULTS: A total of 48 patients (37 female, 11 male) were compared. The average age of onset was 48 years; 36 patients had distal extremity involvement (75%), 5 proximal (10%), and 7 both proximal and distal (15%). Among 33 patients in which the dystonic side was known, 20 were affected on the left (61%). Inversion of the foot with flexion of one or more toes was the most prevalent pattern in those with distal extremity involvement. DISCUSSION: This is a novel task-specific dystonia triggered during ambulation that is often misdiagnosed as an orthopedic or psychogenic issue.