Sinus histiocytosis (Rosai-Dorfman disease) clinically limited to the skin.

Sinus histiocytosis with massive lymphadenopathy (SHML) is an idiopathic proliferation of unique histiocytes that have vesicular nuclei and voluminous pale cytoplasm, often with emperipolesis. Pure cutaneous involvement is very rare. We describe a patient with SHML limited to the skin whose lesion has spontaneously regressed. A 35-year-old Korean male visited the Department of Dermatology due to facial rash for 2 months. A 3 x 3.5 cm-sized well-demarcated dark erythematous nontender plaque was noted on the right cheek. Skin biopsy showed dense, nodular infiltrates of histiocytes with abundant cytoplasm and vesicular nuclei rimmed by lymphoplasma cell aggregates throughout the upper and mid-dermis. The histiocytes were immunohistochemically positive for S-100 protein and CD68, but negative for CD1a. Laboratory tests and a thorough physical examination revealed no abnormalities. These findings suggested that this was a case of SHML clinically limited to the skin. The skin lesion was initially resistant to steroid therapy, but began to regress 10 months after the onset without further treatment.