Pattern VEPS, SEPS and BAEPS in Parkinson's disease

Recovery functions of somatosensory evoked potentials in parkinsonian patients

The aim of this study was to analyze the recovery functions of median nerve somatosensory evoked potentials (SEPs) and to clarify changes in the somatosensory system of patients with Parkinson's disease (PD). The central and frontal SEPs and the nerve potential of the median nerve were examined. The latencies and amplitudes of SEPs produced by a single shock in patients with PD were normal. The recovery functions of central SEPs showed a low degree of suppression in patients with PD, although the recovery curve of the nerve potential in PD patients was almost normal. The change in recovery curves of SEPs in patients with sensory complaints were more noticeable than that in patients without sensory disturbance. A low degree of suppression of central SEPs might play a role in the sensory complaints of PD patients.

Abnormalities of short-latency somatosensory evoked potentials in parkinsonian patients

Twenty-two patients (16 affected by parkinsonian syndromes, 6 by other neurological diseases) and 12 age-matched controls were examined. Short-latency somatosensory evoked potentials were recorded from 30 scalp electrodes in the 45-52 msec following separate left and right median nerve stimulation at the wrist. Bit-colour maps were generated on a 4096 pixel matrix via quadratic interpolation. Peak latencies and amplitudes of the parietal, central and frontal components were evaluated. Moreover, the amplitude ratios between parietal and frontal components on the same hemiscalp and between peaks on homologous right and left scalp districts were taken into account. The unique significant difference between parkinsonians and controls was represented by a depressed frontal N30 wave. This peak was absent in 3 and reduced in 7 out of 16 parkinsonians, with an overall abnormality rate of 47% of the examined arms. Average maps pooling data of parkinsonians and controls confirmed the presence of reduced evoked activity for the whole duration of wave N30 on those mid- and parasagittal frontal districts where this peak is maximally represented in normals. A similar abnormality was found in 1 of the 6 non-parkinsonian neurological patients suffering from a meningioma of the falx compressing the left supplementary motor area. Possible pathophysiology of such wave N30 abnormalities in parkinsonians is discussed.

Alteration of visual evoked potentials and electroretinograms in Parkinson's disease

A group of 24 patients with Parkinson's disease (PD) with normal fundi and normal visual acuities was examined electrophysiologically. Checkerboard reversal VEPs and ERGs (P-ERGs) at various contrast levels as well as photopic and scotopic luminance ERGs were recorded and compared with an age-matched group of controls. Earlier reported latency increases of the VEPs of the patients were confirmed for patterns of high contrast only. Scotopic and photopic luminance ERGs of the patients showed normal latencies, but at all light intensities the amplitudes of the scotopic and photopic b wave, as well as the amplitudes of the photopic a waves, were significantly reduced, P-ERG amplitudes were reduced at 50% contrast. Identical results were obtained in patients under dopaminergic treatment (n = 17) and in patients who did not receive any treatment (n = 7). These results suggest that alterations occur already at the retinal level where dopamine receptors have been found. Thus the reported changes of the VEP are not caused by the visual cortex alone.