N30 wave amplitude of somatosensory evoked potentials from median nerve in Parkinson's disease: a pharmacological study.

We studied N20 and N30 waves of Somatosensory Evoked Potentials from median nerve stimulation in different pharmacological conditions. N30 wave amplitude was decreased in 33 parkinsonians without therapy in comparison with a group of age-matched normal subjects. In a group of 19 parkinsonians, N30 wave amplitude was significantly augmented during apomorphine infusion and less evidently, but still significantly, during chronic 1-dopa therapy. The administration of an oral dose of haloperidol in 11 normals did not affect significantly the studied parameters. The infusion of apomorphine in 6 psychotic patients with extrapyramidal symptoms secondary to long-term treatment with neuroleptics, determined, together with a clear-cut clinical amelioration, a significant increase of N30 amplitude and N30/N20 ratio. Possible pathophysiological hypothesis of such electrophysiological modifications are discussed.