The spectrum of disorders presenting as adult-onset focal lower extremity dystonia

Background: Uncommonly, adult-onset dystonia is confined to one lower extremity. We sought to characterize the clinical spectrum associated with the presenting phenotype of lower limb dystonia including foot torsion. Methods: Retrospective computer search of the Mayo Clinic Medical Records Linkage System (1996-2006). Inclusion criteria were (1) a principal, initial diagnosis of monomelic lower extremity dystonia with foot torsion; (2) no neurologic findings outside of the affected limb; (3) age-onset > 18 years. Prospective data were sought from apparent idiopathic cases. Results: We identified 36 patients (31 females) presenting with monomelic lower limb dystonia including foot torsion. Onset was usually subacute or insidious (32 patients); mean symptom duration was 28.8 months (range, 1-96), age-onset 47.5 years (range, 21-77). After a mean follow-up of 3.1 years, causes were identified in over half, including 5 with parkinsonism. Other treatable etiologies included psychogenic dystonia (3 patients) and stiff-limb syndrome (2 patients). Post-traumatic dystonia was diagnosed in 10 patients and consistently manifested as fixed, painful foot torsion, in contrast to the action-induced dystonia in 5 parkinsonism cases, and 10 of 14 patients with primary lower limb dystonia. Imaging identified the cause in only 1 patient (ischemic stroke) and was negative in the single patient with pyramidal signs. Conclusions: Adults presenting with monomelic lower limb dystonia with foot torsion often have an identifiable cause, sometimes treatable, including Parkinson's disease (diagnosed with levodopa trial) or immune-mediated stiff-limb syndrome. Post-traumatic dystonia was the single most frequent cause and proved difficult to treat. Unlike certain other series of such patients, psychogenic dystonia was an uncommon clinical diagnosis.