Cutaneous Rosai-Dorfman disease with increased number of eosinophils: coincidence or histologic variant?

Rosai-Dorfman disease (RDD) is characterized histologically by a dense histiocytic infiltrate with emperipolesis and associated lymphocytes, plasma cells, and neutrophils. Eosinophils are not commonly associated. We report a patient with initial thymus and pituitary gland involvement by RDD, who later developed papules on the groin and axilla. Skin biopsies showed admixed histiocytic infiltrates (lymphocytes, neutrophils, and plasma cells) without emperipolesis. A prominent eosinophilic infiltrate was also observed, a feature not, to our knowledge, previously reported. Immunohistochemistry revealed positivity for CD68 (most cells) and S100 protein (scattered cells) and was negative for anti-CD1a. The diagnosis of RDD was established in the clinical context after comparison with the thymic and pituitary lesions (similar histologic features, albeit with fewer eosinophils, and immunohistochemical profiles). We present the first case, to our knowledge, of multicentric RDD with cutaneous involvement and associated prominent eosinophilic infiltrate. Thus, RDD should be included in the differential diagnosis of mononuclear infiltrates containing eosinophils.