PURPOSE: Gabapentin is a recently available anticonvulsant whose mechanism of action remains unknown. We suspected efficacy from serendipitous observations of gabapentin in patients with parkinsonism. This led us to a double-blind, placebo-controlled, crossover trial.

PATIENTS AND METHODS: We administered gabapentin in a placebo-controlled, double-blind, crossover trial to 19 subjects with advanced parkinsonism. We measured the effect of placebo and gabapentin on subjects' symptoms with the Unified Parkinson's Disease Rating Scale, the Webster Scale, and the Hoehn and Yahr Scale. We assessed tremor with surface-recorded electromyography.

RESULTS: Total Unified Parkinson's Disease Rating Scale improved with gabapentin compared with placebo (P = 0.0005). Likewise, activities of daily living and examination subscore of the Unified Parkinson's Disease Rating Scale improved with gabapentin compared with placebo but did not achieve statistical significance. Webster Scale showed improvement but neither Hoehn and Yahr Scale nor Webster Scale changes reached statistical significance. Tremor as measured by the Unified Parkinson's Disease Rating Scale improved with gabapentin but the use of the root mean square of the rectified electromyography as a measure of tremor activity was not statistically significant.

CONCLUSIONS: This study demonstrates that gabapentin improves rigidity, bradykinesia, and tremor of parkinsonism including both Parkinson's disease and Parkinson's syndrome. The rigidity and bradykinesia of parkinsonism improve on the drug even when the effects of gabapentin on tremor are discounted.