MONTREAL — The cutaneous features of dermatomyositis often hold the key to making its definitive diagnosis, without having to resort to a muscle biopsy.

So key are the cutaneous manifestations that dermatologists can be a useful resource for rheumatologists faced with a possibly affected patient. “We play a critical role in diagnosing dermatomyositis—we know the visual diagnosis,” Dr. Victoria P. Werth said. The incidence is increasing and the early presentation is often subtle. “We are seeing more of these patients, and they are confusing our rheumatology colleagues.”

Patients can present differently to the dermatology and rheumatology departments at the University of Pennsylvania, Philadelphia, according to a study by Dr. Werth and colleagues (J. Am. Acad. Dermatol. 2007;57:937–43). The degree of skin and/or muscle involvement was the primary distinction among 131 patients who consulted dermatology, 58 who saw rheumatologists, and 13 seen by both specialties.

A correct diagnosis is crucial because dermatomyositis can affect many organ systems beyond the skin, including lung, heart, and muscle. In addition, patients need to be monitored regularly over the long term for malignancies (Ann. Intern. Med. 2001;134:1087–95). Researchers found a relative risk of 2.4 for malignancy among dermatomyositis patients, compared with those who had polymyositis in this retrospective study of 537 patients with biopsy-proven myopathy.

“The adjusted relative risk for malignancy was higher in the first 3 years after diagnosis with dermatomyositis, including for lung, ovary, pancreatic, and other cancers,” Dr. Werth said at the annual conference of the Canadian Dermatology Association. “Risk remains high for years.” She recommended evaluation at least annually.

Cutaneous features include scale, pruritus, and Gottron's papules. A violaceous erythema in a photodistribution pattern or confluent erythema is possible. Also look for Gottron's sign, a symmetrical, macular erythema with or without edema located on the dorsal hand, interphalangeal joints, elbow, and/or medial ankle. Subepidermal vesicles or blisters, vasculopathy, and poikiloderma are among the secondary skin features.

A meeting attendee commented that many patients have extensive scalp pruritus. “Scalp dermatomyositis is very resistant [to treatment]. I have patients where everything else gets better,” Dr. Werth said. “Pruritus is a very big problem. And some patients with only scalp involvement early on get misdiagnosed as seborrheic dermatitis,” added Dr. Werth, who is on the dermatology and medicine faculties at the university.

Dermatomyositis patients often get nasolabial fold involvement, a distinction from systemic lupus erythematous patients. In addition, “nail fold findings are critical,” she said. “It is very important to look at the hands of all our dermatomyositis patients.” Periungual infarcts and telangiectasias are among the characteristic signs.

A definitive dermatomyositis diagnosis includes the typical skin rash and at least three of the following criteria: an abnormal muscle biopsy, abnormal electromyogram (EMG), elevated skeletal muscle-derived enzymes, or symmetric proximal weakness with or without dysphagia or respiratory muscle involvement.

Physicians often ask Dr. Werth if a muscle biopsy is required. “By and large, we can make our diagnosis with a skin biopsy,” she said. Skin findings and an abnormal creatine kinase, EMG, or MRI result are generally sufficient. Make sure to document the muscle disease if a patient is symptomatic, she added. Another attendee asked how to determine if muscle weakness is caused by the disease or by steroid treatment. “You sometimes have to do an MRI,” Dr. Werth replied. “You can also taper the steroid and see if they get better. EMGs can also be helpful. If the patient lets you do a [skin] biopsy, you at least know what you are dealing with,” Dr. Werth said. “We had one patient who we thought had psoriasis—but it was dermatomyositis that had targeted his hand joints.”

Systemic involvement can be quite extensive, Dr. Werth said. Interstitial lung disease, for example, is present in about a quarter of patients. “Cardiac involvement is less common, but still worth looking for,” said Dr. Werth, who is a consultant for Centocor Inc., Aegis Pharmaceutical Ltd., Celgene Corp., Kemia Inc., and Teva Pharmaceutical Industries Ltd.

Topical antipruritic agents and/or corticosteroids are often prescribed as first-line agents for localized skin dermatomyositis, whereas systemic therapy is typically reserved for more widespread disease, according to a review article by Dr. Werth and Rhonda D. Quain, who is now a resident at Mount Sinai School of Medicine, New York (Am. J. Clin. Dermatol. 2006;7:341–51). Antimalarial agents are often used to treat significant skin disease, as are other anti-inflammatory agents, systemic corticosteroids, corticosteroid-sparing immunosuppressants, and more recently, biologics and intravenous immunoglobulin (IVIG).

Dr. Werth cautioned about IVIG in dermatomyositis, however. She cited the case of a hyperviscous dermatomyositis patient who experienced a stroke while on IVIG therapy.

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Cutaneous features such as violaceous erythema and Gottron's papules can hold the key to diagnosing dermatomyositis. Courtesy Dr. Victoria P. Werth

Skin Involvement Is Key in Dermatomyositis Diagnosis