The first step of the two-step algorithm of dermoscopy aims at differentiating melanocytic from nonmelanocytic pigmented lesions, using a stepwise evaluation for the presence of specific dermoscopic criteria. The purpose of this article is to heighten awareness of clinicians to nonmelanocytic lesions that defy the two-step algorithm, thus simulating melanocytic lesions dermoscopically. Seborrheic keratosis, solar lentigo, dermatofibroma, and supernumerary accessory nipple may present with network-like structures. Seborrheic keratosis, dermatofibroma, subcorneal hemorrhage, basal cell carcinoma (BCC), and cutaneous metastases of breast and other cancers may contain pigmented globules. Peripheral streaks can also be seen in seborrheic keratosis and BCC. Homogenous bluish pigmentation, simulating a blue nevus, can also be seen in benign vascular lesions, Kaposi sarcoma, radiation tattoo, and BCC. This overlap of features between melanocytic and nonmelanocytic lesions suggests that integration of all dermoscopic features in the lesion, rather than a stepwise evaluation, may facilitate reaching the correct diagnosis in select cases as outlined in this article.
*Dermatology Service, Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York
Address correspondence and reprint requests to: Ashfaq A. Marghoob, MD, Dermatology Service, Memorial Sloan-Kettering Cancer Center, 160 East 53rd Street, 2nd floor, New York, NY 10022, or e-mail: firstname.lastname@example.org.