| 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 is derived from poly- 'many' myos- 'muscle' and -itis 'disease'. 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]