Seeing Double: Two Cases of Dermatomyositis Misidentified as Erythema Dyschromicum Perstans

Abstract

Without pathognomonic skin lesions or muscle weakness, early DM may be misdiagnosed as a disorder of hyperpigmentation. A 38-year-old male presented with a one-year history of progressive hyperpigmented patches on the face and neck. Outside biopsy was thought to be consistent with EDP, with which the patient’s identical twin brother had recently been diagnosed. Later skin exam was notable for progression to erythematous and hyperpigmented slightly scaly macules and patches of the face, faint pink thin plaques on bilateral extensor forearms and bilateral retroauricular creases, and proximal nailfold capillary dilation and dropout. These findings raised concern for dermatomyositis. Repeat biopsies were suggestive of CTD. ANA was weakly positive. Extended myositis panel was negative. Re-evaluation of his twin brother’s biopsy showed similar findings. The twin’s ANA was negative, and extended myositis panel is pending. Ultimately, both were diagnosed with DM. Work-up for muscle and systemic involvement is underway. Our patient was started on MMF 500mg BID, which was increased to 1000mg BID at follow up. After little improvement on MTX, the patient’s twin brother was switched to MMF 1000mg BID. Diagnosis of DM is particularly challenging in patients lacking classic dermatologic findings or myopathy. Recognition of subtle signs of DM, histopathologic analysis, and presence of MSAs may aid in correct diagnosis.