The classical presentation includes symmetric proximal muscle weakness and underlying malignancy and is very common in adult patients. The etiology is unknown, however.
Some studies suggest people with certain HLA subtypes are at higher risk, and various infectious and pharmacological triggers are suspected to play a role in the pathogenesis of dermatomyositis. Infectious causes include Coxsackie B, enterovirus, and parvovirus. Drugs such as antineoplastic agents, antibiotics, and NSAIDs have been found to be triggers.
The pathogenesis of dermatomyositis involves immune-mediated damage to muscle capillaries and the endothelium of arterioles. In the typical humoral immune response, complement activation occurs. One mechanism of damage in dermatomyositis occurs when the membrane attack complex formed at the end of the complement process deposits in blood vessels, causing inflammation. B cells, autoantibodies, and interferon overexpression may also play a role in damaging the vasculature and muscle fibers. Hypoxia leads to muscular atrophy, resulting in degeneration and death of the fibers. On muscle biopsy, a perivascular and perimysial inflammatory infiltrate, perifascicular atrophy, and microangiopathy may be present. Skin histology reveals vacuolar changes in the basal layer, a lymphocytic infiltrate, and increased mucin production in the dermis.
On clinical examination, patients will have proximal muscle weakness and a skin rash that may include Gottron’s papules, heliotrope erythema, V-sign, shawl sign, holster sign, scalp erythema, midfacial erythema, and photosensitivity. Scalp erythema in dermatomyositis is highly linked to pruritus, alopecia, and telogen effluvium. Patients may experience small fiber neuropathy in dermatomyositis.
Serologies for this patient, who had previously been diagnosed and treated for dermatomyositis, were significant for a positive ANA 1:2560. Anti-Jo-1 antibody was negative. Her liver function tests, aldolase, creatinine kinase, sedimentation rate, C-reactive protein, and serum protein electrophoresis were normal. Imaging revealed mild chronic interstitial lung disease. A malignancy workup was negative.
Treatment of dermatomyositis involves lifestyle changes and pharmacologic therapy. Because of the intense photosensitivity, patients should be diligent with their sun protection. Methotrexate, azathioprine, and mycophenolate mofetil are considered first-line therapies for dermatomyositis. Therapies such as cyclophosphamide, rituximab, IVIg, and plasmapheresis may also be indicated in severe or refractory cases. Additionally, patients with pulmonary involvement should be given systemic steroids. The side effects of these drugs must be considered in the context of the patient’s demographics, comorbidities and lifestyle.
This case and the photos were submitted by Lucas Shapiro, BS, of Nova Southeastern University College of Osteopathic Medicine, Fort Lauderdale, Fla., and Natalie Y. Nasser, MD, of Kaiser Permanente Riverside Medical Center, Riverside, Calif. The column was edited by Dr. Bilu Martin.
Dr. Bilu Martin is a board-certified dermatologist in private practice at Premier Dermatology, MD, in Aventura, Fla. More diagnostic cases are available at mdedge.com/dermatology. To submit a case for possible publication, send an email to email@example.com.
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