Somatosensory, motor and special visual evoked potentials to single and double stimulation in "Parkinson's disease" an early diagnostic test?

Diagnosis of Parkinson's disease is not yet possible with neurophysiological methods. Therefore we investigated the median somatosensory and visually evoked potentials (SEP and VEP) to single and double stimulation, VEP using a special stimulation technique and motor evoked potentials (MEP) employing spinal and transcranial stimulation. In Parkinson's disease the absolute and relative refractory periods of cortical N1 peak of SEP did not differ from that of normal subjects. After single stimulation the cortical N20 latencies were only in 2 of 17 cases delayed. In 8 of 10 cases central conduction time was normal. Also the SEP peaks of brain stem were normal and there was no correlation between symptomatology and SEP results. The data of motor evoked potentials (MEP) demonstrated in all patients a normal central motor conduction time of 5.0 msec. In 30% of patients the VEP data showed a significant delay of P2 latency, independently of clinical status or age. But there were no more P2 alterations after special visual stimulation techniques. In contrast to a good clinical effect in 14 of 19 patients with end-off-dose akinesia, an improvement of P2 delay could not be noticed during a chronic L-dopa and deprenyl therapy.