Rosai-dorfman disease with massive cutaneous nodule on the shoulder and back.

Rosai-Dorfman disease is a rare, idiopathic, benign, and self-limiting histiocytic proliferative disorder. A 26-year-old man presented with a single massive cutaneous nodule (reaching 30 cm in diameter) on the left shoulder and back for 15 months. The routine hematological and biochemical tests were normal. Magnetic resonance scanning showed the lesion involved the skin, subcutaneous tissue, and subjacent muscle group, accompanied by obvious lymph node enlargement in the left part of the neck, supraclavicular fossa, and axillary fossa. The histopathology of the left cervical lymph node revealed diffuse effacement of the normal nodal architecture, with patchy chronic inflammatory cell infiltrates comprising lymphocytes and sheets of histiocytes. Some histiocytes contained lymphocytes within their pale cytoplasm. Many multinucleated giant cells were found; however, caseating granulomas were not seen. The skin and muscle biopsy specimen obtained from the back revealed infiltrating lymphocytes and histiocytes diffusely distributed in the dermis, subcutaneous tissue, and crevices of the muscle fibers. The phenomenon of emperipolesis and the presence of multinucleated giant cells were also seen. Immunohistochemical staining revealed that the histiocytes were positive for S-100 protein and CD68 but negative for CD1a. Immunophenotyping of the infiltrating lymphocytes indicated positive reactions to CD3, CD45RO, CD5, CD7, CD4, CD8 (partly), CD79a, CD20 (partly), and Ki-67 (<1%). The final diagnosis was Rosai-Dorfman disease. Owing to the extensive and deep involvement of the subcutaneous tissue and muscles, the patient did not undergo surgery to excise the massive skin nodule. The lesion showed no obvious change at the 12-month follow-up.