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.
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Epidemiology
The incidence is 2 in 1,000,000 ref and it typically affects women more than man at a 2:1 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 1.
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 2 as well as features of pulmonary fibrosis (e.g. reticular opacity, honeycombing) ref.
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 3