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Acquired amalgam tattoo. A possible diagnostic pitfall

A 60-year-old woman was referred for evaluation of an asymptomatic pigmented lesion located on the lower left gingival mucosa, which was present for 1 year. On physical examination, an asymmetrical, 6 mm, oval, blue-blackish macule, with irregular borders, was observed (Fig. 1). The rest of the physical examination was unremarkable. There was no lymphadenopathy and the patient did not report any personal or family history of skin cancer. The patient reported that he had had a dental prosthesis in contact with the lesional area until 15 years ago. Under examination with dermoscopy, there was a black color macule with no pigment network, but with multiple black dots all over the surface. At the periphery of the lesion, radial parallel linear extensions of pigment asymmetrically arranged, simulating radial streaming (Fig. 2), were also seen. Under local anesthesia, a 3-mm punch biopsy was obtained. Histological study showed a mucosal hyperplasia with an inflammatory lymphocytic infiltrate within the dermis. In the reticular dermis, granular deposits and larger globular aggregates of dark granular material were found. This material was distributed among the interstice and in the macrophages cytoplasm (Fig. 3) and did not stain with iron or melanin stains. A diagnosis of acquired amalgam tattoo was made.