MUSCLE ULTRASTRUCTURE IN REYE'S SYNDROME (RS): EVIDENCE FOR A MYOPATHY

Abstract

Biochemical studies have shown elevation of muscle creatine phosphokinase (Roe et al., Ped. 55:119, 1975) and excessive urinary nitrogen losses up to 0.64 g/kg/day (Snodgrass and DeLong, N. Eng. J. Med. 294:855, 1976) in RS, suggest ing skeletal muscle injury. We report electronmicroscopy of muscle biopsies obtained from 15 RS cases on the day of admission and at followup 4 days to 23 weeks later. A myopathy of variable severity was present in each case acutely. In severely affected specimens about 1/40 muscle cells were necrotic with dissolution of the sarcolemma,loss of striations and dispersion of myofilaments, producing a homogenous matrix which contained vesicular fragments of sarcoplasmic reticulum, autophagic vacuoles and spherical mitochondria with expanded matrix and frequently ruptured outer membranes. Surrounding muscle cells were abnormal, displaying glycogen loss, ribosome disorganization, dilation of sarcoplasmic reticulum and intramyo-fibrillar edema. There were 2 populations of mitochondria in muscle cells: Individual mitochondria demonstrated extreme matrix expansion suggestive of that seen in brain and liver in RS, but the majority of muscle cell mitochondria demonstrated only slight matrix expansion. Muscle cell triglyceride was increased and many cells contained myelin figures. Inflammation was absent but influenza virus was isolated from 3 of 5 biopsies in which cultivation was attempted. These studies confirm the existence of a myopathy in RS. The relationship between the myopathy of RS and post-influenzal myopathy of childhood should be investigated.