Hypomyopathic dermatomyositis

Hypomyopathic dermatomyositis is a rare systemic autoimmune disorder of the skin with little to no muscle involvement. It makes up <5% of all dermatomyositis diagnoses.

Epidemiology

The incidence is 2 in 1,000,000 and it typically affects women more than man at a 2:1 .

Clinical presentation

Symptoms include fatigue, joint pain, fevers and/or dysphagia. Signs include periorbital violaceous plaques (heliotrope rash), Grotton papules (hand extensor surfaces),​ Raynaud phenomenon and/or a non-erosive inflammatory polyarthritis. Clinical muscle weakness is absent .

Pathology

Associations

• increased risk of cancer
• rapidly progressive interstitial lung disease (RP-ILD)

Microscopic appearance

• muscle/skin biopsy: dense lymphocytic infiltrate and atrophy of muscle fibers

Markers

• autoimmune panel: positive antinuclear antibodies (ANA) and anti-MDA5 antibody
• creatine kinase: elevated

Radiographic features

With pulmonary involvement, CT can demonstrate diffuse ground-glass opacity as well as features of pulmonary fibrosis (e.g. reticular opacity, honeycombing) .​

Treatment and prognosis

• immunosuppressive therapy: tacrolimus, cyclosporin, prednisolone
• anti-histamine medication: hydroxyzine
• avoidance of sun exposure
• cancer screening as appropriate to age, there is some debate as to whether increased screening would be warranted