Noun | 1. | myasthenia gravis - a chronic progressive disease characterized by chronic fatigue and muscular weakness (especially in the face and neck); caused by a deficiency of acetylcholine at the neuromuscular junctions disease of the neuromuscular junction - a disease characterized by impairment of neuromuscular junctions autoimmune disease, autoimmune disorder - any of a large group of diseases characterized by abnormal functioning of the immune system that causes your immune system to produce antibodies against your own tissues |