A case of a primary cutaneous plasmacytoma presenting in adolescence.

Primary cutaneous plasmacytoma is defined as monoclonal proliferation of plasma cells that arises primarily in the skin without evidence of systemic disease. We present an extremely rare case of a young adult diagnosed with solitary plasmacytoma. A 20-year-old woman presented with a pruritic erythematosquamous indurated plaque on the inner aspect of her right thigh. She had undergone a biopsy 5 years ago, and under the diagnosis of Nekam disease, she was treated with topical steroids followed by intralesional injections of triamcinolone acetonide. A new skin biopsy revealed infiltration of the epidermis by small T lymphocytes while plasma cell accumulations were found in the dermis. Immunostains for light and heavy chains [kappa, lambda, immunoglobulin (Ig) G, IgA, and IgM] demonstrated IgG/κ monoclonality of the plasma cells. On molecular analysis, T-cell receptor and immunoglobulin heavy chain rearrangements were polyclonal. Serum protein electrophoresis, immunofixation, and quantitative assessment of serum Igs were normal. Bone marrow biopsy, skeletal survey, and body computed tomography scan were unremarkable. A diagnosis of primary solitary cutaneous plasmacytoma was made. The lesion was removed surgically, and the patient remains in remission up to now. Primary cutaneous plasmacytoma represents only 2%-4% of extramedullary plasmacytomas. The rarity and the nonspecific presentation of cutaneous plasmacytomas does not allow a definite clinical diagnosis. Only histopathology reveals the typical pattern of a dense monomorphic dermal plasmacytic infiltrate, whereas immunohistochemistry shows monoclonality of the neoplastic cells.