ORLANDO – There was a median 1-year delay between the onset of symptoms and diagnosis of classic dermatomyositis, and a 17-month delay before diagnosis of amyopathic dermatomyositis, based on a review of 232 dermatomyositis patients seen at the University of Pennsylvania, Philadelphia.

Just 103 (44.4%) patients were diagnosed with dermatomyositis (DM) right out of the gate. Among the other 129, 48 (37.2%) were diagnosed with lupus, 38 (29.5%) with undifferentiated connective tissue disease, 10 (7.8%) went undiagnosed, and 33 (25.5%) were diagnosed with rosacea, psoriasis, rheumatoid arthritis, fibromyalgia, lichen planus, and a number of other conditions. By the time the DM diagnosis was finally confirmed, almost every patient had Gottron’s papules or sign.

Misdiagnosis of dermatomyositis (DM) is nothing new, but the study brings home just how common the problem is, even at a major academic medical institution.

One of the take homes is that clinicians should never forget about the possibility of DM even when patients are diagnosed with other autoimmune diseases, and remain vigilant for erythema on the lateral thighs or nasolabial fold, Gottron’s papules, and other diagnostic giveaways, the researchers said.

“Biopsies for lupus and DM can be essentially identical,” with interface dermatitis and dermal mucin found in both. “We see a lot of patients misdiagnosed with” cutaneous or systemic lupus, said investigator Basil Patel, MD, a research fellow at the university.

Interface dermatitis, in particular, can’t be relied on to differentiate the conditions. A better option is checking for lupus bands and membrane attack complexes on direct immunofluorescence.

There’s also just not enough awareness that dermatomyositis can present without the classic muscle symptoms and findings, i.e. clinically amyopathic DM. While 49 of 120 patients with classic dermatomyositis (40.8%) were misdiagnosed or undiagnosed in the study, the number rose to 80 of 112 (71.4%) among amyopathic patients.

“We saw that there was a much higher rate of misdiagnosis in patients who didn’t have any muscle disease. We have to raise awareness that amyopathic dermatomyositis is a very prevalent condition,” Dr. Patel said at the International Conference on Cutaneous Lupus Erythematosus.

“There might be some level of subclinical muscle activity where, if you did an MRI, you might see inflammation, but the patient doesn’t report any symptoms. There are also patients that don’t have any muscle findings on MRI, or elevated muscle enzymes, but still have the skin findings,” he said.

Perhaps the markedly increased risk of cancer in DM, especially within a year or 2 of symptom onset, is the strongest argument for earlier diagnosis. “There’s also a risk of interstitial lung disease, so making sure that you’re getting pulmonary function tests and age-appropriate malignancy screening in a timely fashion is very important,” Dr. Patel said.

Also, although many of the initial treatments for DM – sun protection and topical steroids and calcineurin inhibitors, for instance – are the same as for cutaneous lupus, medications like mycophenolate mofetil and methotrexate are used more readily. The sooner DM is recognized for what it is, the sooner patients can get relief, he said.

Almost all the patients were white women. The majority were 40-80 years old.

There was no industry funding for the work, and Dr. Patel didn’t have any disclosures.

aotto@mdedge.com

SOURCE: da Silva DM et al. Presented at the 2018 International Conference on Cutaneous Lupus Erythematosus

Timely dermatomyositis diagnosis, treatment remain elusive