Cutaneous Rosai–Dorfman disease preceding inguinal lymphadenopathy

A 33‐year‐old man presented with asymptomatic, gradually progressing, reddish nodules on the thigh of 1 year's duration. Six months later, nodules were noticed on the buttock of the same side. At the same time, the inguinal and femoral lymph nodes increased in size and could be seen as an elevated mass in the groin which, although painless, made the patient limp when walking. On examination, a cluster of pink nodules on an erythematous, oval, indurated area, measuring 10 cm × 5 cm, was seen on the lower medial aspect of the right thigh ( Fig. 1). A small, almost circular, cluster of papules was present on the lower part of the right buttock. Some of these lesions, according to the patient, were reducing in size. The right inguinal and femoral lymph nodes were markedly enlarged and firm. The overlying skin was normal. Clinical differential diagnoses of dermatofibrosarcoma and localized, cutaneous T‐cell lymphoma were considered in this patient. Systemic examination revealed no abnormality. 1Cluster of reddish nodules over the thigh Routine investigations showed a normal hemogram with an erythrocyte sedimentation rate (ESR) of 25 mm/h. Urinanalysis, serum proteins, liver and renal function, chest X‐ray, and paranasal sinuses were within normal limits. Peripheral blood smear examination did not show any abnormal cells. Immunoglobulin (Ig) levels showed: IgG, 12.9 g/L (reference range, 5.6–14.5 g/L); IgA, 4.6 g/L (reference range, 0.45–3.64 g/L); IgM, 0.7 g/L (reference range, 0.03–2.09 g/L). An incisional biopsy was taken from the skin lesion and fine needle aspiration (FNA) of the inguinal nodes was performed. FNA smears were moderately cellular. The cell population, predominantly polymorphic, comprised mature lymphocytes, plasma cells, neutrophils, and histiocytes. The histiocytes were large, having abundant cytoplasm, and the most prominent feature was the presence of lymphocytes and plasma cells engulfed within the histiocyte cytoplasm (emperipolesis) ( Fig. 2). Skin biopsy from the lesion showed an essentially unremarkable epidermis. The entire dermis was densely infiltrated by a polymorphic inflammatory cell population. The predominant cell population was made up of large histiocytes having abundant pale cytoplasm. Plenty of lymphocytes arranged in a nodular pattern were also seen between the histiocytes. Plasma cells, neutrophils, and a few eosinophils were also interspersed. The striking feature was, however, engulfed neutrophils and lymphocytes within the histiocyte cytoplasm (emperipolesis) ( Fig. 3). Immunohistochemical stains revealed S‐100 positivity in the histiocytes ( Fig. 4). The cytologic, histologic, and immunohistochemical findings were correlated and a diagnosis of Rosai–Dorfman disease was made. 2Photomicrograph of fine needle aspiration smears showing large histiocytes with engulfed lymphocytes and plasma cells (emperipolesis) (Giemsa, × 400)3Photomicrograph from the cutaneous nodule showing a dermal infiltrate of histiocytes, lymphocytes, neutrophils, and plasma cells. The large histiocytes reveal emperipolesis (hematoxylin and eosin, × 400)4Photomicrograph from the skin lesion showing a positive staining reaction with S‐100 antibody within the histiocyte cytoplasm (avidin–biotin peroxidase, × 400)