Dysmaturation Neuromyopathy: Correlation with Minimal Neuropathy in Sural Nerve Biopsies

Dysmaturation (neuro)myopathy without specific histochemical or cytoarchitectural characteristics accounts for many cases of hypotonia in infancy. We obtained a maturation profile for type I and type II fibers from birth to 6 years of age, from which a classification of fiber dysmaturation based on fiber-type hypotrophy and coefficient of fiber variation is presented. We analyzed the morphometric, ultrastructural, and single fiber teasing findings in the sural nerve of ten infants with hypoto-nia and dysmaturation myopathy based on the above classification. Data on endoneurial area, myelinated fiber density, proportion of large (> 6 μm) myelinated fibers, unmyelinated fiber density, regression analyses of myelin area:axon area, and mean myelin thickness were developed. Abnormalities in large myelinated fiber density (3 cases), disturbances in my-elination index (5), and single fiber teasing abnormalities in internode length (1) were found. Ultrastructural abnormalities were observed and classified as group 0 changes similar to the five control nerves; group 1, in which rare fibers showed de-generation or basement membrane duplication; and group 2, which was characterized by multiple abnormalities including degenerate nuclei, amyelinate fibers, degeneration/regeneration, excessive basal lamina reduplication, and hypomyelina-tion. This study provides evidence that minimal neuropathic abnormalities are present in the sural nerve of infants carrying a diagnosis of dysmaturation neuromyopathy. (J Child Neurol 1988;3:276-291). odern histochemical and electron micro