VANCOUVER, B.C.– On histology, pathologists are unable to reliably differentiate between cutaneous lupus erythematosus and dermatomyositis. So it falls to clinicians to sort out what’s what based on the patient’s clinical presentation.
“Dermatomyositis is a disease of muscle and skin, but as dermatologists we should view this as primarily a dermatologic disorder, because the diagnosis is made on the skin,” Dr. Jan Dutz said at the annual meeting of the Pacific Dermatologic Association. “The pathology is not diagnostic. Therefore, it’s up to you to make the diagnosis based on the characteristic patterns of dermatomyositis: the changes of the violaceous erythema on the face and arms, the Gottron’s papules, and the changes in blood vessels.”
Dr. Jan Dutz
Enlarged and decreased capillaries are a hallmark clinical feature of dermatomyositis, which can be observed by examining the proximal nail folds. “It turns out that you can look at those capillaries and predict the severity of the disease, so that those who have improvement in the capillaries following early treatment usually have less severe disease,” said Dr. Dutz, professor of dermatology and skin science at the University of British Columbia, Vancouver.
Like cutaneous lupus erythematosus, dermatomyositis is a type 1 interferon-mediated disease. The genes inducible by type 1 interferon alpha have increased expression in muscle and in peripheral blood lymphocyte, and interferon alpha administration can induce disease. Researchers recently described a new subset of dermatomyositis based on an investigation of 77 patients with the disorder (J. Am. Acad. Dermatol. 2011;65:25-34). Of these, 10 (13%) had anti-MDA-5 (melanoma differentiation associated gene 5) antibodies, which are antibodies to a protein related to the interferon pathway. Most of the patients (8 of 10) tested negative for antinuclear antibody. The clinical features were palmar papules, ulcerations (usually on the back of the hands), MDA-5 antibody, and an increased risk of interstitial lung disease. “Ulceration had an odds ratio of almost 20 with being associated with this antibody and this syndrome,” said Dr. Dutz, who was not involved with the study. “So if you see these papules and you see these ulcerations on the hands, it increases the chance of interstitial lung disease.”
These clinical features also have been observed in cases of juvenile dermatomyositis (Arthritis Res. Ther. 2014;16:R138). “These patients get skin ulcerations, oral ulcerations, and have a high incidence for arthritis, mild muscle disease, and interstitial lung disease,” he said.
Dr. Dutz said that he often turns to antimalarial agents as the first treatment option for patients with dermatomyositis. If they don’t respond, he typically switches them to methotrexate. “If that doesn’t work, I usually try mycophenolate mofetil or IVIG [intravenous immunoglobulin], which is one of the most effective treatments for dermatomyositis,” he said. “Studies keep on emphasizing this. There’s also some interest in using rituximab in patients with resistant disease.”
Dr. Dutz disclosed that he is an advisory board member for Janssen, AbbVie, Amgen, Leo Pharma, Roche, and Novartis. He has also conducted clinical trials for Centocor and Ono Pharmaceutical Co.
On Twitter @dougbrunk