Alteration of SEP topography in Huntington's patients and their relatives at risk.

We studied the amplitude maps of median SEP parameters in patients with Huntington's disease (HDP) and their relatives at risk (HDF). Corresponding to the small amplitude of SEP in HDP, the power (microV2) was significantly smaller at all electrodes, and the maximum power was shifted anteriorly as a result of greater reduction of the power in the parietal than in the frontal region. In HDF, significant power reduction at the parietal region resulted in a similar anterior shift of the power to that noted in HDP. In addition to the overall reduction of SEP amplitude, the field distributions of parietal N20, frontal N29 and central N60 were significantly different in HDP, as compared to the normals. The typical relationship of the frontal positive and parietal negative fields normally present at N20 latency was lost in HDP due to the loss of the frontal P20. Frontal N29 was absent. Also N60 field shifted anteriorly. In HDF, the degree of deviation was in between those of HDP and normals. These alterations of SEP amplitude, wave form and field distribution in HDP and in some of HDF may be viewed as a result of aberrant modulatory effect exerted by the non-sensory system upon the somatosensory input.