By Gary M. White, MD
Dermatomyositis (DM) is a systemic disorder associated with characteristic skin changes (e.g., periorbital swelling, red papules on the knuckles) and symmetrical muscle weakness of the proximal limbs. With regard to the muscle changes, muscle enzyme elevation, characteristic electromyogram (EMG) abnormalities, and muscle biopsy alterations are seen. Variants include juvenile, paraneoplastic, and amyopathic.
Periorbital edema with a violaceous hue is the classic heliotrope rash of dermatomyositis. A photodistributed eruption may be seen on the chest, upper back, and arms. Violaceous, scaly changes may occur over bony prominences, such as the knuckles, elbows, and scapula. Periungual erythema and telangiectasias occur. Hypertrichosis may occur rarely, especially in DM of childhood. The Jo-1 antibody correlates with pulmonary disease. Dermal collagen implants may pose a small but significant risk for the development of dermatomyositis. A dermatomyositis-like syndrome has been reported with acute HBsAg-positivity [JAMA 1978;239;959] and with hydroxyurea therapy [BJD 1995;133;455]. Scaling and fissures on the lateral and palmar aspects of the fingers may occur (mechanic's hands).
The term Gottron papules may be an outdated one, as it suggests a limited presentation [JEADV 2016;30;689]. Skin changes over the knuckles may include papules, nodules, and plaques. The appearance may be erythematous, whitish (lichen-sclerosis-like), poikilodermatous, and even crusty with ulcerations. CD44v7, a cell adhesion molecule, was found to be induced by mechanical stretching and along with osteopontin (increased expression in response to mechanical trauma) appears to produce Gottron papules [JAMA Derm 2016;152;1062].
Gingival telangiectasias has been reported as a relatively common occurrence in juvenile dermatomyositis [AD 1999;135;1370]. Other mucous membrane findings include edema, erosions, ulcers, and leukoplakia-like areas.
Scalp involvement may lead to significant alopecia [JAMA. 28;272:1939-41]. Patients are often misdiagnosed as having seborrheic dermatitis or psoriasis. There may be significant pruritus. It is often treatment-resistant. Treatment involves:
Various drugs have been reported to either cause or exacerbate dermatomyositis. Those include ipilimumab, hydroxyurea, anti-TNF agents, and zoledronic acid among others.
Hydroxyurea-induced MD-like eruption may be indistinguishable clinically from true DM, but it tends to be asymptomatic, characteristically lacks myositis, and is frequently associated with leg ulcers.
A subset of patients with dermatomyositis have antibodies to MDA-5 (melanoma differentiation-associated gene 5). These patients are remarkable for normal ANA, palmoplantar or fingertip erythema, ulcerations (e.g., on the back of the hands) and an increased risk of interstitial lung disease [JAAD 2011;65;25-34].
Patients with DM and antibodies to TIF-1g (41% in one study) tend to have more extensive skin disease, as well as palmar hyperkeratotic papules, psoriasis-like lesions, and hypopigmented and telangiectatic patches [JAAD 2015;72;449].
Proximal muscle weakness is the classic systemic sign. Patients may have trouble raising their arms above their head, rising from a chair, or squatting. Diagnosis may be aided by muscle enzyme elevation (check CPK, aldolase), muscle biopsy, and/or electromyography. MRI may be helpful in identifying muscle involvement and localizing it for biopsy. A subset of patients with skin disease but without muscle involvement (called amyopathic dermatomyositis) has been described. Lesions representing panniculitis may also occur in DM, both adult and juvenile. Various radiologic imaging studies have been recommended to localize muscle involvement. If needed, a radiologist should be consulted.
About 18-20% of DM patients do not have muscle involvement [BJD 2016;174;158]. About 3/4 of these patients are women [AD 2010;146;26]. The diagnosis must be made clinically with the aid of skin histology as there is no muscle pathology to confirm. These patients still need a screen for malignancy and regular pulmonary function tests. Some of these patients will go on to develop muscle disease.
There is an approximate 20% incidence of cancer in adults but not for children under 16 years of age. The risk for ovarian cancer is significantly higher in women. A search for an internal malignancy should be done, primarily through a thorough H&P and screening labs. Only very rarely has neoplasia (lymphoid tumors, neuroblastoma, and hepatocarcinoma) been associated with DM in children. The subset of patients with dermatomyositis sine myositis have a similar if not identical risk of neoplasia [J Rheum 1996;23;101].
Tests for antibodies against anti-transcriptional intermediary factor-1 (TIF-1 gamma) and nuclear matrix protein (NXP-2) have been found predictive for DM-associated cancer [Arthritis & Rheumatism Sept 2013]. In one study, 83% of DM patients with cancer reacted to NXP-2 or TIF-1 gamma.
Rarely, the following may be associated: Bronchiolitis obliterans organizing pneumonia [JAAD 1999;40;328], severe subcutaneous edema [Dermatologica Sinica 2014:32:97], dysarthria, and an inability to swallow even saliva.
Therapy should be done in conjunction with the dermatologist, primary care physician, rheumatologist, and other specialties as indicated. Below is just an overview.
The primary goals of treatment are to 1) identify and treat any malignancy, 2) eliminate muscle weakness, and 3) have patients off systemic steroids. Paradoxically, it is usually best to treat patients aggressively with systemic steroids at a dose of about 1 mg/kg initially, tapered to 0.5 mg/kg over about 6 months. Then, slow reduction and ultimate discontinuation of the steroid in 2 years time is desirable. For patients with only skin involvement, sunscreens and hydroxychloroquine should be given.
All patients should be encouraged to avoid the sun using sunscreen, hats, and protective clothing.
Prednisone, e.g., 60 mg/day, is usually effective and is the treatment of choice for patients with muscle disease. For children, higher doses, e.g., 2 mg/kg/day, may be needed.
Hydroxychloroquine 400 mg/day and chloroquine 500 mg/day are good alternatives.
Low-dose MTX, e.g., 2.5-30 mg/week, can be very helpful [JAAD 1997;36;67]. It is often used in conjunction with prednisone, e.g., 10-20 mg QOD.
Mycophenolate mofetil is usually very effective and may be given for skin disease without muscle involvement. Azathioprine may be used as well, e.g., 100 -150 mg/day.
IVIG can be very effective for both juvenile and adult patients with DM [JAAD 2013;69;654]. IVIG may also help patients with DM-associated calcinosis [JAAD 2015;73;174].
Tofacitinib, an oral JK inhibitor, was beneficial in three patients resistant to other therapies [JAMA Derm 2016;152;945].
Rituximab and sirolimus have been used. In one study of 18 patients with DM resistant to steroids, approximately 80% improved with rituximab [J Drugs Dermatol 2017;16;162]. For children with DM, prednisone and, if needed, MTX may be started initially. If these fail, IVIG may be added.
Anti-TNF agents should be avoided as they can exacerbate myositis and interstitial lung disease as well as increase the risk of infection.
Violaceous plaques over the knuckles.
Periungual telangiectasias and erythema.
A photodistributed rash.
In severe cases, a diffuse rash.
Diffuse, red, itchy scalp in dermatomyositis.
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