Histologic features of cutaneous sinus histiocytosis (Rosai‐Dorfman disease): study of cases both with and without systemic involvement

Sinus histiocytosis with massive lymphadenopathy (Rosai-Dorfman disease) is a systemic proliferation of cells that resemble the sinus histiocytes of lymph nodes. Whereas initial reports highlighted the often striking cervical adenopathy, more than 40% of patients have extranodal involvement. Cutaneous lesions are the most common form of extranodal disease, but cases that present as cutaneous disease without lymph node involvement are rare. We examined biopsies from three patients with cutaneous lesions of sinus histiocytosis, none of whom had detectable systemic involvement, and compared them to those of two patients whose lymph nodes were involved by the disease. The histology of skin lesions in all five cases showed dense nodular or diffuse infiltrates of "histiocytes," emperipolesis of lymphocytes, neutrophils, and plasma cells. "Histiocytes" were present in lumens of dilated lymphatics. At the peripheries of the lesions were lymphoid aggregates and thick-walled vessels surrounded by plasma cells. Staining with anti-S-100 protein antibody showed marked cytoplasmic positivity in the "histiocytes" in each case. The only features that differed among the two groups were the presence of pseudoepitheliomatous hyperplasia and infiltrates of eosinophils in one case in which the disease was limited to the skin. We believe that cutaneous sinus histiocytosis can be specifically diagnosed by skin biopsy. Because cutaneous sinus histiocytosis may be unfamiliar to general pathologists, dermatopathologists, and dermatologists, cases limited to the skin may be under-recognized.