The levodopa test in Parkinson's disease.

The clinical diagnosis of Parkinson's disease may be difficult. In elderly patients there may be other causes of the triad of rigidity, bradykinesia and tremor. This study was designed to assess whether a single levodopa challenge could predict dopa responsiveness in patients with Parkinson's disease. Twenty-two of 27 newly diagnosed patients completed the study. Of the 22, 17 (77%) responded positively to the initial test and five (23%) showed no response. At 1 month, 18 (82%) were improved on treatment and four (18%) were not. Thus the initial test predicted 17 (94%) of the 18 who responded at 1 month and correctly identified the response of 21 (95%) of the 22 patients. There was only one false negative result. Patients with negative results turned out to have other parkinsonian syndromes. A positive levodopa test helps to confirm the diagnosis of Parkinson's disease and a negative test should alert one to alternative diagnoses.