Inflammatory myopathy (
inflammatory muscle disease or
myositis) is disease featuring weakness and inflammation of muscles and (in some types) muscle pain. The cause of much inflammatory myopathy is unknown (
idiopathic), and such cases are classified according to their
symptoms and
signs and
electromyography,
MRI and laboratory findings. The main classes of idiopathic inflammatory myopathy are
polymyositis (PM),
dermatomyositis (DM), and
inclusion-body myositis (IBM).