Differential diagnosis of an oral amalgam tattoo mimicking oral mucosal melanoma: A case report and literature review

Amalgam tattoo, a commonly encountered exogenous oral pigmentation, is benign but can occasionally pose diagnostic challenges due to its clinical resemblance to oral mucosal melanoma. This report presents a case of a 55-year-old female patient with a 10-mm pigmented lesion on the right mandibular gingiva. The lesion exhibited asymmetry, border irregularity, and color variegation, characteristic features of oral mucosal melanoma. Notably, the right mandible had no teeth restored with amalgam or other foreign materials, and radiography revealed no metal materials. Intraoperatively, the lesion not only abutted the bone surface but also showed pigmentation extending beyond the periosteum. However, histopathological analysis revealed dense black particles resistant to melanin bleaching, surrounded by CD68- and LCA-positive lymphohistiocytic cells, confirming the diagnosis of amalgam tattoo. In this report, we review the literature on amalgam tattoos presenting with features resembling oral mucosal melanoma, including the present case, and emphasize their distinguishing characteristics.