A disease of the muscles.

Myopathy has many causes. Some myopathies are present at birth, called congenital. Other causes are autoimmune conditions. In these conditions, the body's immune system attacks its own muscles by mistake. Other conditions and some medicines also can cause myopathy. Anyone can have myopathy.

Muscle weakness is the main symptom of myopathy. Other symptoms may include muscle pain, muscle stiffness and trouble breathing.

Treatment depends on the type of myopathy.