Neurophysiological study in Pelizaeus-Merzbacher disease

Abstract

The neurophysiological characteristics of Pelizaeus-Marzbacher disease (PMD) were studied in four Japanese patients aged between 5 and 13 years. Pendular spontaneous nystagmus was always recorded with a frequency between 2.5 and 4 Hz, and abnormal saccades with an almost twofold prolongation in onset time and 50% decrease in velocity were noted. Brainstem auditory evoked potentials consistently demonstrated severely altered waves II to V, following a normal wave I, despite normal hearing acuity. Somatosensory evoked potentials (SEPs) were always absent between brainstem components and early cortical responses. Late cortical components of SEPs and visual evoked potentials with significantly prolonged latencies were recorded in the three younger cases having normal sensory and visual acuity (N35 of SEP, 73.1 ± 2.1 ms; N75 of VEP, 129.0 ± 12.7 ms; mean ± S.D.), while these peaks were absent in the oldest case having the most severe handicap. In motor evoked potentials (MEPs), R1 of blink reflex with significantly prolonged latency (14.9 ± 1.48 ms) was always obtained, and no subsequent R2 was elicited. Magnetic transcortical stimulation elicited no MEPs of the thenar even in the facilitating condition on voluntary contraction despite mild weakness of the thenar, while normal MEPs were always elicited on cervical stimulation. These electrophysiological findings were consistent with extensive conduction slowing involving the brainstem to the cerebrum, which seemed to be accompanied by conduction block in motor systems rather than sensory systems. Although each of the results was not specific, in combination they suggested the characteristics of diffuse brain dysmyelination in PMD.