Postexcitatory inhibition after transcranial magnetic stimulation of the motor cortex in patients with drug-induced parkinsonism and in healthy individuals.

The duration of the postexcitatory inhibition after transcranial magnetic stimulation was investigated in 16 patients with drug-induced parkinsonism and in 20 healthy control individuals. In the patients, the chlorpromazine-equivalent of the neuroleptic medication was determined, and the severity of the drug-induced parkinsonism was measured using the Simpson-Angus Scale score. Group comparison (U-test) revealed a significant shorter postexcitatory inhibition in patients than in control individuals. Regression analyses showed a negative correlation between the Simpson-Angus scale score and the duration of the postexcitatory inhibition. The correlation only reached significance for a group of patients who received at least one butyrophenone derivate. No clear-cut relation was found between the chlorpromazine equivalent and the postexcitatory inhibition. These results indicate that drug-induced parkinsonism shares features of genuine Parkinson's disease. Furthermore, it seems possible to assess the extrapyramidal side effect of butyrophenone derivates, but not for other neuroleptic drugs, by means of the method described.