Study of deterioration in long-term treatment of parkinsonism with L-dopa plus decarboxylase inhibitor.

35 parkinsonian patients have been treated over 3 years with L-Dopa combined with benserazide. After an impressive improvement during the first months of treatment a slow but significant deterioration of the patient's condition was observed. At the end of the observation period however their condition was still significantly better than before starting the treatment. A reduced mean L-Dopa dosage was ruled out as the cause of this deterioration. Withdrawal of the L-Dopa therapy for a few days in 13 patients provided strong evidence that it is due to the progression of the disease and to a partial loss of L-Dopa efficacy.