Abstract: A collection of plasma cells in the skin can represent a broad spectrum of disease entities. Secondary syphilis, primary cutaneous plasmacytoma, primary cutaneous plasmacytosis, cutaneous lymphoid hyperplasia and nodular amyloidosis are considered possible differential diagnoses. The primary cutaneous plasma cell disorders can range from malignant to benign plasma cell neoplasms. The malignant conditions are neoplastic diseases having monoclonal proliferations, rapid progression and fatal outcome while the benign plasma cell disorders usually show polyclonality, chronicity and benign process, including plasmacytosis. We present a case of cutaneous plasmacytosis. The patient was a 34-year-old man, presented with disseminated reddish-brown plaques and nodules on the right side of the hips, inguinal groove, and the thigh. Histopathologically, mature plasma cells perivascular infiltrates were observed mainly in the dermis. Polyclonality of infiltrating plasma cells with coexistence of both kappa and gamma chain-positive cells demonstrated with immunohistochemistry, as well as CD20+++, CD38++++, CD79a++++, CD138++, Ki67＜30%. The diagnosis, cutaneous plasmacytosis, was established by the pertinent laboratory findings. Primary cutaneous plasmacytosis was an uncommon reactive lymphoplasmacytic disorder of uncertain etiology. Cutaneous plasmacytosis is a rare disease characterized by peculiar multiple eruptions and hyper gamma globulinemia. It has been mainly described in patients of Japanese descent, with only few reports in Caucasians and Chinese, although information concerning the disorder was limited to individual case reports. Cutaneous plasmacytosis is a rare disorder, which is characterized by multiple red to dark-brown nodules and plaques on the trunk and usually associated with polyclonal hyper gamma globulinaemia. Primary cutaneous plasmacytosis or cutaneous plasmacytosis was thought to be a reactive process with unknown etiology. Histologically, lesions contain dense perivascular infiltration of mature polyclonal plasma cells without any atypia, in the dermis and subcutaneous fat. The clinical course is chronic and benign without spontaneous remission. Available treatments for cutaneous plasmacytosis include psoralen ultraviolet A radiotherapy, systemic chemotherapy and intralesional steroid injection. The patient with cutaneous plasmacytosis in this report was treated with tacrolimus ointment and psoralen ultraviolet A.

Key words: Plasmacytosis, Skin disease, Case reports