Clinical variability of congenital myopathy with type I fiber atrophy: A long‐term observation of three cases

The variable clinical courses of three cases of congenital fiber type disproportion (CFTD) over a period of 10 years are presented. All showed improvement in early childhood, but subsequently, varying degrees of deterioration were noted: specifically, marked deterioration in case 2 and decreased muscle strength in case 3. Maximal motor function levels were attained differently among the cases. Histological findings included type 1 fiber hypotrophy and increased internal nuclei in common in all cases. Fine structural changes, such as patchy areas of myofibrillar degeneration, were noted in cases 1 and 2 (second biopsy), and cytoplasmic bodies were seen in case 2 (second biopsy). Myotubes were noted in case 3. The degree of cyto-architectural changes did not correlate with clinical severity. The heterogeneity of CFTD is also discussed.