The light and electron microscopic changes in the skeletal muscles during paralysis in thyrotoxic periodic paralysis.

Light microscopy of the biopsied quadriceps muscles during paralysis in 17 patients with thyrotoxic periodic paralysis (TPP) showed no abnormalities in 23.5 per cent, sarcolemmal nuclear proliferation in 35.5 per cent, atrophy of muscle fibers in 29.4 per cent, central nuclei in 23.5 per cent, fatty infiltration in 17.6 per cent, vacuolation in 11.8 per cent, and sarcoplasmic masses in 11.8 per cent. The muscle specimens were also examined by electron microscopy in ten of these patients; the main changes observed were vacuolation (90 per cent), mitochondrial abnormalities (100 per cent), glycogen granules accumulation (100 per cent), disruption of the myofibers (50 per cent), and changes in the T-system (40 per cent). The light and electron microscopic changes in the skeletal muscles during paralysis were not well correlated with the severity of the muscle weakness of hypokalemia.