Response to levodopa treatment in dopa-responsive dystonia

Background: Dopa-responsive dystonia (DRD) is similar to Parkinson disease in that both disorders have impaired dopamine synthesis and respond to levo dopa treatment. Dopa-responsive dystonia differs in that dopamine storage i s intact in contrast to Parkinson disease in which it is markedly reduced. Objective: To examine the short- and long-duration responses to levodopa do sing in subjects with DRD. Methods: The response to brief infusions of levodopa was examined in 4 subj ects with DRD and the effects of withdrawal of levodopa for 3 to 7 days stu died in the 3 subjects receiving long-term levodopa therapy. Motor function was measured with tapping speed, Unified Parkinson's Disease Rating Scale motor score, and global dystonia score. Results: The short-duration response to levodopa dosing seems to develop mo re slowly and persists longer in subjects with DRD than in subjects with Pa rkinson disease. Withdrawal of levodopa leads to a gradual decline in tappi ng speed and reemergence of dystonia over several days, similar to the rate of decay of motor function in Parkinson disease. The short- and long-durat ion responses were not clearly differentiated in DRD. Conclusions: This pilot study suggests that retained dopamine storage in DR D may prolong the short-duration response and blur the distinction of the s hort- and long-duration responses. The decline in motor function in DRD on withdrawal of long-term levodopa therapy resembles that in Parkinson diseas e, suggesting that a long-duration response, if it exists in DRD, is unrela ted to dopamine storage.