A pure Cutaneous Rosai-Dorfman disease: case report and a review of the literature.

Background: Cutaneous Rosai-Dorfman disease (CRDD) is a rare variant of benign histiocytic proliferative disorder limited to the skin. The underlying etiology is still unclear, but it had been claimed that infections, immunodeficiencies, and autoimmune disorders might have a role in the etiology of this disorder. The characteristic presentation of RDD is lymphadenopathy due to abnormal production and accumulation of histiocytes in lymph nodes; however, the extra-nodal areas could also be affected, such as cutaneous. Herein, we presented a 45-year-old Iranian woman presented with an atypical pure cutaneous Rosai Dorfman disease, in addition to a summarized list of atypical cases of RDD that are reported as pure cutaneous RDD with atypical presentation. Case presentation: Herein, we presented a 45-year-old woman who referred to us with an ulcerative nodule with a size of 5×5 cm on her buttock, gradually growing over one year. After the primary evaluations, a biopsy specimen was obtained, and histologic studies revealed a dense cellular infiltrate involving the dermis and the subcutis, which was composed of abundant sheets of large histiocytes with admixtures of lymphocytes, plasma cells, neutrophils, and eosinophils within their cytoplasm -known as the emperipolesis phenomenon. The immunohistochemistry staining was positive for S100 and CD68 and negative for CD1a. Conclusion: The diagnosis of CRDD was confirmed based on these histopathological findings.