A diagnostic challenge: inflamed and pigmented seborrheic keratosis. Clinical, dermoscopic, and histopathological correlation.

Pigmented and irritated types of seborrheic keratosis (SK) can be confused with melanoma, basal cell carcinoma, or pigmented actinic keratosis. Dermoscopic examination may give many clues for the diagnosis of SK, but in equivocal cases the accurate diagnosis can only be made by microscopic features. Herein, we report a striking, isolated pigmented and inflamed SK, located on the waist in an elderly man. Although the duration of the lesion was not clear, a recent change in color was reported. The striking dark pigmentation and lack of visible characteristic features for SK led us to consider other pigmented lesions, mainly melanoma, which it closely resembled. Dermoscopic examination was inconclusive with subtle clues for SK, such as brown-gray dots, small brownish clods, a few curved short lines, and few small pinkish round structures. Histopathological and immunohistochemical examinations revealed an inflamed and pigmented SK. In conclusion, pigmented and inflamed SK does not usually tend to show typical dermoscopic features of SK and may mimic other pigmented lesions, including melanoma. All skin lesions that cannot be classified as clearly benign should undergo biopsy.