Hematophagic histiocytosis. A report of 23 new patients and a review of the literature.

The clinical and laboratory features of 23 new patients as well as 50 previously reported patients with the syndrome of hematophagic histiocytosis are reviewed. The syndrome occurs more often in men than women but has no age predilection. Common presenting features include fever, hepatic and splenic enlargement, lymphadenopathy, and profound depression of blood counts. The clinical course is generally fulminant and may be complicated by coagulation abnormalities, hepatic dysfunction and renal failure. In the majority of patients, however, the syndrome is self-limited with resolution of the clinical and laboratory abnormalities within several weeks. Hematophagic histiocytosis generally occurs in patients who develop infections in the setting of preexisting immunologic abnormalities or neoplasms. Viral infections are most commonly involved, but virtually any other infectious agent can precipitate this syndrome. The characteristic morphologic feature of the hematophagic histiocytosis is the proliferation of mature histiocytes actively ingesting other blood cells. These hematophagic histiocytes most commonly involve the bone marrow but may also be present in the lymph nodes, spleen and liver. Other bone marrow abnormalities include hypocellularity with preservation of megakaryocytes, and myelofibrosis. The principal features of this syndrome that distinguish it from malignant histiocytosis are the cytologic maturity and degree of hematophagic activity of the histiocytes as well as its more favorable prognosis. In some patients, however, a clear distinction of malignant from reactive histiocytosis will not be possible until a clonal marker for malignant histiocytes is identified. Based in our experience, the syndrome of hematophagic histiocytosis appears to be more common than malignant histiocytosis.