Pigmentation of osteoma cutis caused by tetracycline.

Blue nodules developed in the skin of a patient with acne concomitant with the start of tetracycline therapy. When removed, these nodules were brown and histologic examination revealed a lamellate structure compatible with bone. Under ultraviolet light, these osteomas fluoresced yellow, indicating the presence of tetracycline. This suggests that tetracycline, combined with new bone formation, causes pigmentation of osteoma cutis.