Effects of chronic levodopa and pergolide treatment on cortical excitability in patients with Parkinson's disease: a transcranial magnetic stimulation study

Objectives: Transcranial magnetic stimulation was used to assess the effect s of chronic levodopa and pergolide treatment on motor cortex excitability in Parkinson disease (PD). Methods: Motor thresholds, intracortical inhibition and facilitation were s tudied at baseline and after 6 and 12 months of therapy in 10 PD patients a nd compared to 7 age-matched controls. Results: At baseline, there was significantly less intracortical inhibition with only a slight reduction of intracortical facilitation in PD as compar ed to controls. Relative to pretreatment condition, levodopa restored intra cortical inhibition for 12 months while pergolide did not. Intracortical fa cilitation was always within the normal range. Motor thresholds were unchan ged in both groups of patients over 12 months. Clinically, levodopa and per golide improved motor Unified Parkinson's disease rating scale (UPDRS) scor es at 6 months but only levodopa maintained benefit at 12 months as compare d to baseline. Conclusions: Levodopa and pergolide differentially affected cortical inhibi tory circuits at 12 months. The progressive deterioration of restored intra cortical inhibition with pergolide may be due to the development of toleran ce and down-regulation of dopamine receptors. (C) 2000 Elsevier Science Ire land Ltd. All rights reserved.