Myasthenia gravis is a chronic muscular disorder characterized by weakness and rapid fatigue of any of the muscles under voluntary control. Signs and symptoms include weakness of arm and leg muscles, double vision, drooping eyelids and difficulties with speech, chewing, swallowing and breathing.
Approximately 15 percent of people with myasthenia gravis have a tumor in their thymus gland, located under the breastbone. Mediastinal tumors are benign or cancerous growths that form in the area of the chest that separates the lungs called the mediastinum.
