Electron microscopic study of extraocular muscles in myotonic dystrophy.

The extraocular muscles of two middle-aged men with ophthalmoplegia secondary to myotonic dystrophy were studied by electron microscopy. The main change was disorganization in the arrangement of myofibrils rather than degeneration of the cells. Diseased muscle cells contained randomly distributed, short and irregular myofibrils and individual myofilaments. The cytologic appearance of these muscle cells was similar to that of developing muscle cells. The pathogenesis of the myopathy in myotonic dystrophy may be related to myofibrillogenesis and its maintenance.