Myopathies are diseases that primarily cause damage to muscles. They may be present at birth (congenital) or occur due to nutritional imbalances, injury, or ingestion of a poisonous substance. Myositides are diseases that produce a mainly inflammatory reaction in muscle. Common causes include infections, parasitic diseases, and immune-mediated conditions.
Muscle weakness or damage can also occur as a sign of many different disorders (such as nerve trauma or influenza).