Parkinson's disease and somatosensory evoked potentials: apomorphine-induced transient potentiation of frontal components.

We recorded somatosensory evoked potentials (SEPs) to median nerve stimulation from parietal and frontal districts in 32 patients with Parkinson's disease by evaluating latency/amplitude characteristics of the parietal P14-N20-P25 and of the frontal P20-N30-P40 wave complexes before and 10, 20, 30, and 60 minutes after subcutaneous administration of apomorphine chloride. The frontal complex N30-P40 was smaller than normal in 17 patients in baseline recordings. Following apomorphine, the parietal responses did not significantly vary in amplitude, but the frontal complex showed a remarkable amplitude potentiation in 22 of 32 patients (68.7%, p < 0.001), 19 of whom were also improving clinically. Amplitude potentiation was evident 10 minutes after apomorphine and faded away nearly in parallel with the end of its clinical efficacy. There were no SEP changes in three healthy controls after apomorphine.