Vacuolar changes in neuromuscular disorders: a morphometric study.

BACKGROUND: Vacuoles in muscle represent a nonspecific alternation and are found in a variety of neuromuscular disorders. To understand their significance, a morphometric study of the vacuolar formation in muscle biopsies from 340 patients was reviewed.

METHODS: Vacuolar changes in muscles were found in 24 out of 340 patients with muscle biopsies. The specimens were prepared for histopathological, histochemical and electron microscopic examinations. The location, size, shape, number and content of the vacuoles were recorded. The number of fibers containing vacuoles was also assessed.

RESULTS: Observed after modified Gomori trichrome stain, there were rimmed and non-rimmed vacuoles. Rimmed vacuoles were found in limb-girdle myopathy with rimmed vacuoles (5), oculopharyngeal muscular dystrophy (1). inclusion body myositis (2) and neurogenic disorder (1). These vacuoles were usually cleft-like in shape in 5-16% of muscle fibers with a diameter of 3-20 microns. An elevation of acid phosphatase activities and the presence of cytoplasmic debris suggested an autophagic process. In 15 patients with non-rimmed vacuoles, round and oval shapes with variable sizes and numbers were noted. Four with acid maltase deficiency (AMD) had numerous vacuoles containing glycogen, while three with lipid storage disease contained lipid. Interestingly, in AMD the size of the vacuoles was usually more than 10 microns in diameter, but less than 5 microns in lipid storage disease. In other diseases including polymyositis (5), Duchenne muscular dystrophy (2) and hypokalemic periodic paralysis (1), the numbers of vacuoles were usually fewer than three in each fiber.

CONCLUSIONS: Vacuolar changes were not specific, but morphometric analysis of the vacuoles may provide some clues in differential diagnosis. The vacuoles were usually numerous in glycogen and lipid storage diseases, while rimmed vacuoles may be found in limb-girdle myopathy with rimmed vacuoles, oculopharyngeal muscular dystrophy, and inclusion body myositis.