Neonatal myotonic dystrophy in a premature infant: clinical and morphological findings

We report a case of neonatal myotonic dystrophy in a premature infant of 34 weeks gestation. The striking pathological feature in muscle biopsy was severe generalized fiber hypotrophy. Histochemical stains for myofibrillar ATPase revealed a uniform fiber type of intermediate staining characteristics (Type II C). Oxidative preparations showed a light peripheral sarcoplasmic halo without enzymatic activity in most fibers. Ultrastructurally, fiber periphery consisted of a sarcoplasmic rim devoid of myofibrils and mitochondria and rich in glycogen granules and some vesicles. Satellite cells were numerous. Pathologic findings characteristic of the adult form of the disease were lacking. These morphological features were interpreted as a marked delay in fetal muscle maturation. The purpose in this paper is to present the unique pattern of myopathologic findings.