Polymyositis

Polymyositis
Micrograph of polymyositis. Muscle biopsy. H&E stain.
Specialty	Rheumatology

Polymyositis (PM) is a type of chronic inflammation of the muscles (inflammatory myopathy) related to dermatomyositis and inclusion body myositis. Its name means 'inflammation of many muscles' (poly- + myos- + -itis). The inflammation of polymyositis is mainly found in the endomysial layer of skeletal muscle, whereas dermatomyositis is characterized primarily by inflammation of the perimysial layer of skeletal muscles.^[1]