Middle latencies sometosensory evoked potentials in patiens with dementia

There are some reports about the possible change of somatosensory evoked potiential (SEP) in dementia. The middle latency SEP was examined in 45 elderly consisting of 12 patients with multi-infact dementia (MID), 17 with dementia of alzheimor type (DAT) and 16 age-matched normal controls. This study has revealed the following three points : (1) the latensies of N18, P24, N33 and P45 were prolonged in MID. (2) there were no correlations between the severity of dementia and the amplitudes or latensies of each component. (3) The amplitude of P24 and P 45 over 20μV was seen only in DAT. These findings suggest that in DAT the central pathway is ofter intract and that althought the cortical cells are damaged scatteredly, there must be spared cells thoughout its clinical course. On the other hand, in MID the majority of lesions may exist in the subcortical white matter with damage of the central SEP pathways, and most part of the cortex are left intract. This study shows that the amplitude of P24 or P45 over 20μV isa valuable indicator to distinguish DAT from MID.