Histiocytic lymphophagocytic panniculitis. An unusual extranodal presentation of sinus histiocytosis with massive lymphadenopathy (Rosai-Dorfman disease).

A 72-year-old woman presented with the sudden onset of multiple, large, firm, subcutaneous nodules in her right arm and left thigh. Biopsy of the lesions revealed a septal and lobular panniculitis of unknown cause. The lesions regressed spontaneously without therapy over a period of a few weeks. A follow-up review of the microscopic slides from the biopsy disclosed a lymphohistiocytic and plasma cell proliferation with lymphophagocytosis by histiocytes, the characteristic morphological features of sinus histiocytosis with massive lymphadenopathy. This diagnosis was further supported by the immunocytochemical demonstration of S100 protein reactivity within the histiocytic cells. A seven-year follow-up has failed to reveal any evidence of recurrence or progression of the disease. Sinus histiocytosis with massive lymphadenopathy should be entertained in the differential diagnosis of cutaneous lesions presenting with septal and lobular panniculitis.