For a diagnosis of dermatomyositis, patients must present with at least one of the skin symptoms listed in "skin lesions" and four of the remaining symptoms.
For a diagnosis of polymyositis, patients present with no skin symptoms and four of the remaining criteria.
- Proximal muscle weakness (upper or lower extremity and trunk)
- Elevated serum CK (creatine kinase) or aldolase level
- Muscle pain on grasping or spontaneous pain
- Myogenic changes on EMG (short-duration, polyphasic motor unit potentials with spontaneous fibrillation potentials)
- Positive anti-Jo-1 (histadyl tRNA synthetase) antibody
- Nondestructive arthritis or arthralgias
- Systemic inflammatory signs (fever: more than 37° C at axilla, elevated serum CRP level or accelerated ESR [erythrocyte sedimentation rate] of more than 20 mm/h by the Westergren method)
- Pathological findings compatible with inflammatory myositis (inflammatory infiltration of skeletal evidence of active regeneration may be seen)
- Heliotrope rash (red purple edematous erythema on the upper palpebra)
- Gottron's sign (red purple keratotic, atrophic erythema, or macules on the extensor surface of finger joints)
- Erythema on the extensor surface of extremity joints: slightly raised red purple erythema over elbows or knees
Credits: Modified with permission from Tanimoto K, Nakano K, Kano S, Mori S, Ueki H, Nishitani H, Sato T, Kiuchi T, Ohashi Y. Classification Criteria for Polymyositis and Dermatomyositis. The Journal of Rheumatology. 1995;22:4.
Updated March 2012