Abstract
Polymyositis (PM) is an uncommon inflammatory disease of unknown cause, but the disease shares many characteristics with autoimmune disorders. In the past, the diagnosis criteria for PM depended primarily on clinical features, blood enzyme levels, an electromyogram, and muscle biopsies. However, there are still imperfections in the diagnostic criteria of PM. The development of muscle imaging led to revisiting not only the PM diagnosis strategy but also the patients' follow-up. Teaching point: PM should be considered and included in the differential diagnosis of a patient with inflammatory signs and muscular pain, and the radiologist should be aware of its imaging features.