Dopa-responsive dystonia.

DRD is a distinctive clinical entity and an unexpectedly common subgroup of torsion dystonia. Diurnal fluctuation is often but not always present and does not reliably distinguish the disorder from ITD. DRD must be considered in the differential diagnosis of the child or adolescent presenting with a dystonic gait disorder, diplegic cerebral palsy, sporadic spastic paraplegia, ataxic syndromes, and juvenile parkinsonism. The response to L-DOPA is so dramatic and occurs so quickly that a diagnostic therapeutic trial should be undertaken in all patients presenting with these syndromes.