Middle and short latency somatosensory evoked potentials (SEPm, SEPs) in the Rett syndrome: chronological changes of cortical and subcortical involvements.

Middle and short latency somatosensory evoked potentials (SEPm, SEPs) were studied in 11 cases of the Rett syndrome (RS) to detect the chronological changes of cortical and subcortical involvements. The cortical N1 (18) latency was significantly delayed in cases above the age of 5 years. Subcortical components up to N16 which are considered to be derived from the thalamus or the upper brainstem were mostly normal in cases under 9 years of age. However, in those over 9 years, the brainstem component P14 and the cervical cord component N13 revealed a delay in latency. The clavicular component N9 and component N11, which is considered to be from the spinal cord entry, were still normal in our cases. These findings suggested that before the age of 9 years, the revealed lesion in SEP is mainly rostral to the thalamus or upper brainstem. With increasing age and disease process, the involvement of the lower brainstem and the spinal cord becomes apparent. Thus, a degenerative process might be suspected. However, the chronological changes of N1 (18) and N13 parallel to normal development seen in RS indicated that the maturational changes were found up to around the age of 5-6 years in the former and 9 years in the latter, though the mean values of these two peak latencies were slightly higher than those in controls as early as the age of 3-4 years. These observations also indicated developmental, probably metabolic, abnormality underlies the pathogenesis of RS and the degenerative process might overlay in the later period of the disease.