Levodopa responsive parkinsonism in an adult with Huntington's disease.

A patient is reported on with Huntington's disease who, as an adult, first developed severe parkinsonism with bradykinesia, rigidity, postural instability and festinating gait. His clinical signs were similar to those of the Westphal variant of Huntington's disease except that he also had resting tremor and a supranuclear gaze palsy. Magnetic resonance imaging showed caudate and putamen atrophy. Genetic analysis disclosed 49 triple CAG repeats in allele 1 and 17 in allele 2 confirming the diagnosis of Huntington's disease. Treatment with levodopa produced substantial functional motor improvement with a 17 point reduction in the unified Parkinson's disease rating scale (UPDRS) motor subscale including reduction of tremor, bradykinesia, and postural instability. This is the first report of a patient with adult onset Huntington's disease with parkinsonism responsive to levodopa.