N30 somatosensory evoked potentials in patients with unilateral Parkinson's disease.

The N30 component of the somatosensory evoked responses (SEP) was reported as absent or abnormally low in various basal ganglia disorders, including Parkinson's disease (PD), but its relationship to the more affected side in asymmetric disease has not been assessed systematically. In 14 patients with unilateral PD and 10 controls, SEP were performed by stimulating each upper limb and recording from the parietal and frontal contralateral cortex. N30 was symmetric in 4 patients and 4 controls; it was asymmetric in 2 controls and in 8 patients (in 4 the responses were of lower amplitude over the affected hemisphere); no response was elicited in 2 patients and 4 controls. In all patients SEP were recorded off medication; in 9 of them the test was repeated following administration of L-dopa and did not show any significant changes. In conclusion, the N30 was asymmetric in a similar proportion of PD patients and controls. No correlation was found between the affected side and N30 latencies or amplitudes; no change was seen following L-dopa administration as well. The motor deficits and SEP abnormalities in PD probably reflect pathologies in different anatomical structures or functional circuits.