The word myopathy means "disease of muscle." Myopathies are diseases that cause problems with the muscles that control voluntary movements (muscles you can control). These problems range from stiffness (called myotonia) to weakness. They can be mild, moderate or severe..
Mitochondrial myopathies
Metabolic myopathies such as Pompe, Debrancher and McArdle's diseases Myositis is the term for any one of a group of inflammatory muscle disorders. These almost always cause weakness and can cause muscle swelling and pain.
Myositis can sometimes cause difficulty swallowing or breathing.