Pathology of congenital nemaline myopathy. A follow-up study.

This study was undertaken to review the development over 5-18 years of pathologic changes in 13 patients (4 male and 9 female) with congenital nemaline myopathy. Follow-up biopsies were compared with earlier biopsies and with published normal values as to quantity and location of nemaline bodies, secondary signs of myopathy, and in 6 patients as to muscle fiber type and size. Biopsy findings were correlated with the mobility and muscle power of the patient. The main differences in myofiber maturation in the patients as compared with normal myofiber maturation were: (1) deficient differentiation of type 2 fibers, (2) further increase of variation in fiber size with age, and (3) skewing in early adulthood of fiber size distribution curves toward the atrophic end. In ambulant patients, this skew seemed to be compensated with a population of hypertrophic fibers. The nemaline bodies tended to be located beneath the sarcolemma in the younger patients and inside the muscle fibers in the older patients. The quantity of nemaline bodies seemed to have increased with age. The clinical deterioration and the defective myofiber maturation in the patients together with an increase in internal nuclei and endomysial fat or fibrosis indicate an active disease process. This speaks against the generally held view that congenital nemaline myopathy is static.