Sensory and motor evoked potentials in multiple system atrophy: a comparative study with Parkinson's disease.

Somatosensory evoked potentials (SEPs) to median nerve stimulation and motor evoked potentials to transcranial magnetic stimulation (TMS) of the motor cortex were studied in 15 patients with multiple system atrophy (MSA) and compared with matched groups of 20 patients with idiopathic Parkinson's disease (PD) and of 20 normal controls (NCs). No SEP latency or amplitude abnormalities were observed, and, in particular, the frontal N30 component was not significantly depressed. No differences in TMS threshold for evoking responses in relaxed or active thenar muscles were observed. The mean central motor conduction time was normal for the biceps brachii and opponens pollicis muscles and prolonged in the MSA group for the tibialis anterior muscle. Recording SEPs is not useful to differentiate MSA from PD, while the presence of central motor conduction abnormalities may bring into question the diagnosis of idiopathic PD.