Abstract
A 68-year-old female complained of muscle pain and weakness of both thighs resulting in gait and squatting disturbance, pain in the shoulders and knees, and these persisted for 2 months. The patient also complained of ptosis and easy fatigability of extremities. Anti-nuclear factor was positive and anti-acetylcholine receptor antibody was highly elevated, while anti Jo-1 antibody was negative. Ptosis improved on edrophonium test, while muscle power of extremities and gait disturbance did not improve. Muscle biopsy of the thigh demonstrated the irregular degeneration of the muscle fibers, infiltration by inflammatory lymphocytes and neutrophils. Electromyograpy measured in median nerve demonstrated a neuromuscular unit (NMU) of low amplitude and short duration, and waning. These findings were compatible with the simultaneous occurrence of polymyositis and myasthenia gravis. Musle pain, weakness of extremities and gait disturbance were improved by administration of prednisolone, although the complaints of easy fatigability of the extremities and ptosis remained to some extent after gradually tapering the dose of prednisolone. Those complaints were later ameliorated by administration of ambenonium chloride.
