Inflammatory myopathies include polymyositis, necrotizing autoimmune myositis, dermatomyositis, juvenile inflammatory myopathy, and inclusion body myositis. These diseases are classified based on the different clinical and pathological characteristics unique to each of them [1]. Dermatomyositis is a rare disease with an incidence of 6–10 cases/1,000,000 a year with the highest incidence in the 7th decade of life as reported by a Norwegian cohort in a Caucasian population [2].
Diagnosis of dermatomyositis is based on typical signs and symptoms combined with laboratory results, imaging, and electromyography findings and muscle biopsy. Historically, the diagnosis of dermatomyositis was based on the classification criteria named after Bohan and Peter published in 1975. Many other classification criteria were proposed subsequently, the latter by the European League Against Rheumatism/American College of Rheumatology (EULAR/ACR), which were published in 2020 [3].
The clinical features of dermatomyositis are diverse. Skin manifestations can accompany or precede muscle weakness. Classical skin findings include periorbital heliotrope rash and a rash of the upper chest, back, and shoulders, known as the V sign and shawl sign respectively, as well as the Gottron's papules on the knuckles. Another skin appearance is subcutaneous calcifications that break periodically through the skin causing ulcerations. Dermatomyositis usually manifests as a symmetrical proximal muscle weakness but can present with preserved strength called amyopathic dermatomyositis [1].