Seven patients with Fukuyama type congenital muscular dystrophy were studied. Low density areas (LDs) in the cerebral white matter on cranial CT were present in all 4 patients younger than 13 years of age and in 1 of 3 adult patients. LDs corresponded to low signals on T
1 weighted MRI image and high signals on T
2 weighted MRI image. The follow-up MRI showed a decreased tendency of the abnormal signals in 2 patients. Short somatosensory evoked potentials (SSEPs) in two infants, aged 4 months and 8 months, showed absent or depressed N
1 amplitudes and delayed interpeak latencies from P
3 to N
1. N
1 amplitudes increased on follow-up studies. SSEPs of five patients, who were older than 2 years of age, showed normal N
1-P
3 latencies. Amplitude of N
1 was low in 2 patients with LD. Since the absent or depressed amplitude and delayed latency of N
1 improved with the decrease of abnormal signals on MRI, we considered that N
1 abnormalities show delayed myelination.
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