A 57-year-old man discovered a relatively small (1 cm), pigmented nodule of uncertain duration on his left arm during a cutaneous self-examination. The patient had a previous skin cancer.
Key point: The lesion displays an underlying erythema as well as punctuate superficial dark black pigmentation. While this strongly suggests a dysplastic nevus or even a melanoma, pigmented basal cell carcinoma can appear in this manner. A small punch biopsy disclosed basal cell carcinoma with focal hypermelanosis.
Treatment: The lesion was modestly sized and located on a low-risk skin region. Simple excision (with 5-mm borders) and primary closure was performed.
Note: The different diagnostic possibilities can be precise clinical mimics. Biopsy whenever doubt exists regarding the exact diagnosis.