Apomorphine test for dopaminergic responsiveness: A dose assessment study

The clinical diagnosis of idiopathic Parkinson's disease (IPD) remains difficult and is supported by a favorable response to levodopa, while failure to respond represents an exclusion criterion. Recently, the response to subcutaneous apomorphine has been suggested as a tool in predicting levodopa responsiveness in parkinsonian syndromes. We administered apomorphine at doses of 10, 50, and 100 micrograms/kg subcutaneously against placebo over two consecutive days in 37 patients with parkinsonism and evaluated the motor response for 90 min after each dose. Subsequently, we compared the motor response with the follow-up response to levodopa therapy and to a final diagnosis. Twenty-seven patients of 37 showed a positive response to apomorphine, and 10 had a negative response. All positive responses to the apomorphine test were obtained with 50 or 100 micrograms/kg doses. Because of the high frequency of side effects with the dose of 100 micrograms/kg, 50 micrograms/kg seems more useful. After an adequate period of levodopa/carbidopa therapy (12-month follow-up), 29 patients improved; 25 of these had demonstrated a positive response to the apomorphine test. The final diagnosis of IPD, made on the basis of an exhaustive clinical and neuroradiological evaluation and on the response to chronic levodopa therapy, was in good agreement with the response to the apomorphine test (predictivity of diagnosis, 86.4%). Our data indicate that subcutaneous apomorphine at the dose of 50 micrograms/kg is a useful tool in the differential diagnosis of parkinsonian syndromes.