Dermatomyositis
Dermatomyositis is a complement-mediated inflammatory myopathy causing symmetric proximal weakness with pathognomonic skin findings, heliotrope rash and Gottron papules, that separate it from polymyositis. It carries a 3- to 12-fold increased malignancy risk and a distinct interstitial lung disease burden that drive workup and therapy. First-line treatment is high-dose prednisone with an early steroid-sparing agent.
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What this article covers
- Overview
Definition: dermatomyositis is an idiopathic inflammatory myopathy driven by complement-mediated microvascular injury to muscle and skin, distinguished from the other myopathies by pathognomonic skin…
- Epidemiology
Bimodal age distribution: onset clusters in childhood, defining juvenile dermatomyositis at or before age 16 years, and again in the mid-40s to 50s in adults.
- Risk factors
Female sex and the DRB108:01 allele: a roughly 2:1 female predominance and the clearest genetic association, limited in diagnostic value by ethnic variability.
- Pathophysiology
Complement-mediated microangiopathy: deposition of the C5b-9 membrane attack complex in endomysial capillaries causes capillary dropout and tissue hypoperfusion, the initiating injury in both adult and juvenile dermatomyositis.
- Clinical features
Symmetric proximal weakness: neck flexors and shoulder and hip girdle muscles are affected first, causing difficulty rising from a chair or climbing stairs, usually progressing over weeks to months.
- Differential diagnosis
Polymyositis: identical symmetric proximal weakness and creatine kinase (CK) elevation, but without heliotrope rash, Gottron papules, or any characteristic skin finding (polymyositis).
- Diagnosis
The diagnosis is established using the 2017 European League Against Rheumatism/American College of Rheumatology classification criteria, which route symmetric proximal weakness toward dermatomyositis…
- Management
First-line, high-dose glucocorticoid induction: prednisone 1 mg/kg/day PO once daily, up to 80 mg/day.
- Complications
Malignancy: occult cancer in up to 25% of patients within 1 to 3 years of diagnosis, a 3- to 12-fold rate over an age-matched population; ovarian, lung, pancreatic, gastric, and colon cancers and…
- Prognosis
Highly variable course: outcomes range from full resolution to severe, treatment-resistant disease with early mortality; CK elevation at diagnosis does not predict outcome.
- Prevention
No primary prevention of dermatomyositis itself is established; the closest modifiable exposure is discontinuing an implicated drug (statins, interferons, tumor necrosis factor inhibitors, checkpoint inhibitors) when linked to onset.
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