Median nerve somatosensory evoked potentials. Apomorphine-induced transient potentiation of frontal components in Parkinson's disease and in parkinsonism.

Somatosensory evoked potentials (SEPs) to median nerve stimulation have been recorded from parietal and frontal districts in 43 parkinsonians, 17 patients with parkinsonism and 35 healthy controls matched for age and sex. Latency/amplitude characteristics of the parietal P14-N20-P25 and of the frontal P20-N30-P40 wave complexes before and after (10, 20, 30 and 60 min) subcutaneous administration of apomorphine chloride were evaluated in all the 60 patients and in 3 controls. The frontal waves N30 and P40 were either absent or significantly smaller than normal in 31 patients with Parkinson's disease (PD) (72.1%) and in 9 with parkinsonism in baseline records (56.3%). Following apomorphine, the parietal deflections did not significantly vary in amplitude. On the contrary, the frontal complex showed a significant amplitude increase in 27 PD and 8 parkinsonisms (respectively 62.8 and 47.1%); 79.1% of PD and 35.3% of parkinsonisms were improved clinically. Amplitude increase was evident at 10 min after apomorphine, in parallel with clinical improvement, and vanished nearly in coincidence with the end of the clinical effect.