A rare disorder of unknown etiology characterized by distention of the lymph node sinuses and sinusoidal histiocytic infiltration. The histiocytes characteristically contain ingested lymphocytes. Patients present with cervical lymphadenopathy, fever, leukocytosis, and hypergammaglobulinemia. It can affect extranodal sites, including skin, bones, and the respiratory tract. It usually regresses spontaneously.