Early ultrastructural and biochemical changes in muscle in dystrophia myotonica

Muscle specimens from 8 patients with dystrophia myotonica at various stages of the disease have been studied. While the ultrastructural organization of the myofibrils appeared remarkably well-preserved, the sarcotubular system showed well-defined abnormalities which concerned mainly the sarcoplasmic reticulum and varied from discrete swelling to disorganization of the SR structures. The T-system was less severely involved. Longitudinal orientation, however, was found in all cases, while networks of proliferated T-tubules were observed in 1 case. The ultrastructural evidence also supported the view that sarcoplasmic masses are regenerative in nature. The data from studies of the calcium uptake activity of the microsomal fraction indicated that the decreased calcium uptake activity noted in advanced cases was probably due to the dystrophic process. The relevance of these changes to the dystrophic process and to the myotonic phenomenon is discussed.