NEWPORT BEACH, CALIF. – Cutaneous lupus erythematosus and dermatomyositis look identical on histology, so the diagnosis boils down to your clinical exam.
At the annual meeting of the Pacific Dermatologic Association, Nicole Fett, MD, provided clinical pearls on how to differentiate between the two conditions. She began by discussing the case of a 28-year-old female who presents with fatigue, arthralgias, myalgias, photosensitivity, and erythematous scaling papules coalescing into plaques on the face (sparing the nasolabial folds), neck, chest, and bilateral arms and hands (sparing the dorsal hand joints). Earlier in the week, she saw her primary care physician, who ordered an antinuclear antibody test, which was positive at 1:640.
This patient, who was previously healthy, has no known allergies, is on a prenatal vitamin, does not use any drugs or alcohol, is a nonsmoker, and has a family history of autoimmunity, said Dr. Fett, of the department of dermatology at Oregon Health and Science University, Portland. The woman’s clinical findings were most consistent with acute cutaneous lupus erythematosus (CLE).
“Acute CLE spares the nasolabial folds, whereas patients who have dermatomyositis have involvement of the nasolabial folds,” she noted. Examining the hands can also provide clues, as patients with CLE have involvement of the interjoint spaces and sparing of the joints, while patients with dermatomyositis have involvement of the joints and sparing of the interjoint spaces. In addition, patients with dermatomyositis are more likely to have lower extremity involvement, compared with patients who have CLE. “Patients with dermatomyositis will tend to have diffuse scalp involvement that is itchy,” Dr. Fett added. “That is not something you commonly see in cutaneous lupus.”
Other common features of CLE include concomitant discoid lupus erythematosus or another lupus subtype, and mucosal ulcerations, while other common features of dermatomyositis include the Shawl sign and poikiloderma.
The recommended review of systems and exams to assess for systemic lupus erythematosus in CLE patients include asking about photosensitivity, looking for mucosal ulcers, assessing for arthritis, asking about a history of pericarditis or pleuritis, as well as asking about a history of low blood counts, kidney disease, seizures, and malar rash. On cutaneous exam, look for signs of concomitant CLE subtypes, assess for nonspecific cutaneous lupus findings, and evaluate the mucosa. Recommended labs include a complete blood count and an additional workup for anemia, complete metabolic panel, urinalysis, erythrocyte sedimentation rate, C-reactive protein, antinuclear antibody, complement C3 and C4, and antiphospholipid and anticardiolipin antibodies.
The recommended review of systems and exams in patients with dermatomyositis, she said, include assessing for dysphonia/dysphagia, weakness with overhead tasks, weakness when climbing stairs or standing from a seated position, cough, shortness of breath, or dyspnea on exertion, fever, weight loss, night sweats, and pruritus. “When I think about the dermatomyositis patient I think not only about their skin, but about their muscles, lungs and risk of malignancy,” Dr. Fett said. “They have a high risk for developing interstitial lung disease, and about 25% of adult patients are going to have an underlying malignancy.”
She reported having no financial disclosures.