What causes myasthenia gravis?

Myasthenia gravis is a rare condition in which muscle weakness develops in certain parts of the body (especially affecting muscles controlling the head, neck, eyes, extremities and breathing) due to an attack by the body’s immune system. This immune attack interrupts signals between the affected nerves and muscles.

It is not clear why the immune system behaves this way but one clue is that most people with myasthenia gravis have an abnormality in the thymus gland (either enlargement or a tumor). The thymus is a small gland located in the upper chest behind the breastbone that plays an important role in the development of immune cells. Because abnormalities in the thymus are so common in people with myasthenia gravis and because removal of the thymus can sometimes cure the condition, it’s thought that abnormalities in thymus function may cause at least some cases of myasthenia gravis.