Biopsies of this large variegated pigmented plaque ruled out lentigo maligna melanoma and gigantic seborrheic keratosis.
A 72-year-old man complained about an asymptomatic, gradually expanding “spot” on his forehead.
Key point: Physical examination revealed a large variegated pigmented plaque with a palpable surface. Regional adenopathy was absent. The differential diagnosis consisted of a lentigo maligna melanoma and gigantic seborrheic keratosis. Multiple small biopsies were obtained from different sections of the lesion, and all demonstrated benign seborrheic keratosis.
Treatment: The patient was reassured and declined any treatment for cosmetic reasons.
Note: Pre-biopsy dermoscopy was used to attempt to establish the diagnosis. All portions of the lesion did, indeed, demonstrate characteristics consistent with the biopsy-proven diagnosis. While dermatoscopic examination is a very useful technique, biopsy was still indicated to completely assuage the patient’s concerns.