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Don’t trust interface dermatitis to diagnose dermatomyositis


 

REPORTING FROM ICCLE 2018

Dermatologists and rheumatologists are mistaken if they think interface dermatitis is the sine qua non biopsy finding of dermatomyositis (DM), according to David Fiorentino, MD, PhD, professor of dermatology, rheumatology, and immunology at Stanford (Calif.) University.

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Interface dermatitis on skin biopsy is “felt to be almost required by many people to make the diagnosis,” but he and his associates found that it was not present in about a quarter of a cohort of patients with DM. “We don’t want a clinician” to rule out the diagnosis based on its absence on a biopsy, “when its actually quite possible that the patient could have disease,” Dr. Fiorentino said at the International Conference on Cutaneous Lupus Erythematosus.

In general, skin biopsies in DM are tricky. “All of us take them, but we don’t really know how to interpret the information that comes back ... because we don’t really know how often many of [the associated] findings are seen” in DM patients, he noted.

One of the main concerns is to rule out lupus, but interface dermatitis is found in many of its cutaneous forms, as well as in graft-versus-host disease and other diseases.

So what’s a clinician to do? Fortunately, direct immunofluorescence can help. A positive lupus band test helps rule out DM, and the membrane attack complex helps rule it in, both with a good degree of certainty. In a video interview, Dr. Fiorentino explained these tests and how to use them.

Dr. Fiorentino had no relevant disclosures.

aotto@mdedge.com

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