LEVODOPA PEAK RESPONSE-TIME REFLECTS SEVERITY OF DOPAMINE NEURON LOSSIN PARKINSONS-DISEASE

We measured the time to peak antiparkinson response following injectio n of levodopa or apomorphine in 57 patients with Parkinson's disease. The peak response time for levodopa fell from 53 +/- 6.5 minutes in pa tients at Hoehn and Yahr stage I-II, and 28 +/- 4.8 minutes in those a t stage TV (p < 0.0005). There was a significant correlation between l evodopa peak response time and symptom duration (r = 0.65; p < 0.0001) , but there was no relation between apomorphine peak response time and measures of disease severity. Peak response time to levodopa appears to reflect predominantly the status of compensatory presynaptic dopami nergic mechanisms and thus may provide an index to the degree of dopam ine neuron degeneration in parkinsonian patients.