While the etiology remains unclear, some evidence suggests that genetically susceptible individuals with certain HLA types mount aberrant cellular and humoral responses after exposure to malignancy, infection, or drug ingestion.
Clinical features of dermatomyositis can be categorized into cutaneous and systemic manifestations. Typical findings include a heliotrope rash, atrophic dermal papules of dermatomyositis (ADPDM; previously Gottron's papules), shawl sign, holster sign, photosensitivity, flagellate erythema, poikiloderma, calcinosis cutis and nail fold changes. Pruritus is also common.
Systemic manifestations of dermatomyositis include fatigue, malaise, myalgias, and the following:
- Musculoskeletal – Proximal extensor muscle group inflammation that leads to muscle pain and weakness. Patients may have difficulty getting up from a sitting position or combing their hair.
- Gastrointestinal – Dysphagia can be seen due to esophageal muscle involvement.
- Pulmonary – Some level of pulmonary involvement will be present in 15%-30% of patients. Diffuse interstitial fibrosis and acute respiratory distress syndrome are manifestations of pulmonary involvement.
- Cardiac – Tachycardia or bradycardia, bundle branch blocks, cardiomegaly or congestive heart failure.
- Malignancy – Up to 40% of patients with the adult form may have an occult malignancy. Initial cancer screening and vigilant serial monitoring for 2-3 years post-diagnosis is strongly recommended. Chest, abdomen, and pelvis CT scanning – even in the absence of symptoms – should be considered. Commonly found malignancies include colon, ovarian, breast, pancreatic, lung, and gastric cancers and lymphoma. The juvenile form does not share this risk.
- Autoimmune disease overlap – Dermatomyositis can occur in conjunction with systemic lupus erythematosus (SLE), mixed-connective tissue disease, Sjögren syndrome, scleroderma, and rheumatoid arthritis. Scleroderma / CREST syndrome (calcinosis cutis, Raynaud phenomena, esophageal dysfunction, sclerodactyly, and telangiectasia) is the most common overlap syndrome resulting in sclerodermatomyositis.
- Antisynthetase syndrome – Fever, Raynaud phenomenon, "mechanic's hands," interstitial pulmonary fibrosis, polyarthritis, and autoantibodies to aminoacyl-tRNA synthetase.
- Variant – Dermatomyositis sine myositis is the amyopathic form where dermatomyositis is clinically limited to cutaneous involvement. Disease is often detectable on muscle MRI, and many of these patients go on to develop muscle weakness as the disease progresses.
- Variant – Anti-MDA5 antibodies are found in up to 65% of clinically amyopathic dermatomyositis and in 10%-20% of patients with classic dermatomyositis. Their presence has been associated with the development of interstitial lung disease, rapidly progressive lung disease, and poor survival in both US and Asian studies. Anti-MDA5 antibodies have also been associated with mucocutaneous ulceration, palmar papules, nonscarring alopecia, panniculitis, and arthritis.
- Dermatomyositis and Degos disease are, rarely, associated.
- Dermatomyositis may be induced by medications, including hydroxyurea, penicillamine, interferon beta, and ipilimumab.
M33.90 – Dermatopolymyositis, unspecified, organ involvement unspecified
396230008 – Dermatomyositis
- SLE – Violaceous color, heliotrope, and extensor-limited skin disease are not seen in lupus erythematosus (LE). Digital macules and thin plaques typically do not involve knuckles but rather are seen on interdigital skin. Pruritus is not so prominent in LE. Check anti-ds DNA, anti-Sm if considering LE.
- Phototoxic / photoallergic drug eruptions
- CREST syndrome – Can have overlap with dermatomyositis. Refers to a subset of patients with limited scleroderma.
- Polymorphous light eruption – Most lesions resolve within several days' time. Skin lesions are located on all sun-exposed areas, not just extensors. Violaceous color not characteristic.
- Seborrheic dermatitis – No systemic findings. Erythema and scale in sebaceous distribution.
- Systemic amyloidosis
- Contact dermatitis
- Pityriasis rubra pilaris
- Scleroderma – Check for anticentromere antibodies and anti-Scl-70 antibodies. Typified by sclerotic changes in skin not seen in dermatomyositis.
- Graft-versus-host disease – Occurs after allogeneic stem-cell transplantation.
- Mixed connective tissue disease – Check for anti-U1RNP antibody. Most patients are positive for this in mixed connective tissue disease.
- Generalized morphea – Asymmetric induration, no Raynaud phenomenon, no systemic involvement.
- Polymyositis – Without cutaneous findings.
- Acute lesions of erythropoietic protoporphyria may have similar locations, especially on the dorsum of the hands, but usually there is no weakness.
- Atopic dermatitis
- Lichen planus