Seborrheic keratosis (SK) is a frequent motive for consultation and is usually resolved with a simple clinical diagnosis; in private practice, it is often associated with esthetic treatment. Inflammation or pigmentation may require clinical differential diagnosis with squamous cell carcinoma or melanoma, respectively. Dermatoscopy has been of unquestionable help1 by confirming the suspected clinical diagnosis in most cases, even among nonexpert examiners.2 Nevertheless, SK may present a dermatoscopic pattern that is atypical or that mimics other tumors. In this issue of Actas dermosifiliográficas, Mazzeo et al3 perform a retrospective evaluation of a series of 72 SK that had been removed to rule out malignancy. While all the lesions presented characteristic signs of SK, up to 80% presented criteria that suggested a melanocytic lesion, 25% presented polymorphous vessels, whereas 12% of cases of SK presented an overall vascular pattern, and up to 8% presented a blue-white veil. These data are similar to those found in melanomas mimicking SK.4 Although these melanomas may show some signs characteristic of SK, they also show signs that suggest a diagnosis of melanoma, such as presenting 80% of the criteria for a melanocytic lesion, the blue-white veil, and atypical blood vessels. It should be remembered that some forms of SK may mimic melanoma and vice versa; therefore, to ensure that no melanoma goes undiagnosed, a 2-step method has been recommended: ruling out a melanocytic lesion before looking for signs of SK.5 The presence of a combination of blue and black (another specific sign of suspected malignancy6) appears to be rare in atypical SK, but is frequent in melanomas mimicking SK.

In summary, the diagnosis of a lesion suggestive of SK should be confirmed histologically, especially where ablative treatment is considered, when the lesion presents inconsistent dermatoscopic aspects, such as blue-black or blue-white coloring, a pigmented network, globules, or atypical blood vessels.