Exaggerated pigmented granulomatous reaction to the artificial joint implant mimics metastatic melanoma

Total joint replacement is a common orthopedic procedure. An artificial joint implant may fail due to mechanical mishap and a granulomatous reaction can be induced by the artificial joint debris after the mechanical failure. We report a case of an exaggerated pigmented granulomatous tissue response to metallic artificial joint implant debris in a 72-yr-old male that was mistaken for metastatic melanoma. The mass was soft, pigmented, ill-defined, and located in the right inguinal region. Fine-needle aspiration revealed numerous black-pigment laden cells. The cellular features were frequently obscured by the heavy pigmentation. Occasional cells exhibited atypia and prominent nucleoli. There were also abundant extracellular irregular small black particles dispersed in the background. The diagnosis of melanoma involving a lymph node was made. Since there was no prior history of melanoma, it was presumed that this represented metastatic melanoma from an unknown primary. A subsequent exploration of the groin was performed with the intent to resect the disease. At exploration, the mass was found to be contiguous with the hip joint and the frozen section of the mass revealed no evidence of melanoma. The final tissue diagnosis confirmed the frozen section report and showed a granulomatous reaction. This report underscores the diagnostic dilemma associated with the exaggerated pigmented granulomatous reaction due to an artificial prosthesis.