Malignant histiocytosis

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Cytologic appearance of malignant histiocytosis. There are numerous anaplastic round cells surrounding a markedly abnormal giant cell with a bizarre, hyperlobulated nuclear membrane

Malignant histiocytosis (disseminated histiocytic sarcoma) is an aggressive, multisystemic neoplastic diseases characterized by the presence of multiple tumor masses in several organs systems[1].

Organs that are often infiltrated by the neoplastic cells include the lungs, liver, kidneys, spleen, bone marrow, and lymph nodes, with the spleen most commonly affected.

This disease most commonly affects middle-aged Bernese Mountain Dogs, Rottweilers and Golden Retrievers[2], particularly where previous joint disease has been evident prior to diagnosis[3].

Clinical symptoms are often vague, including anorexia, weight loss, fever, and lethargy. Additional clinical signs, such as dyspnea, lameness, episcleritis and neurological deficits, depending on the organ system involved.

Clinical laboratory findings may be quite variable among dogs affected with MH/DHS, and may include anemia, thrombocytopenia, hyperbilirubinemia and rarely hyperferritinemia[4].

A tentative diagnosis can be established by ultrasonography and radiography. Common radiographic abnormalities include the presence of a mediastinal mass, pulmonary nodules or consolidation, hepatomegaly, pulmonary edema and pleural effusion and splenomegaly[5].

A definitive diagnosis requires tissue biopsy of tumors. Histologically, malignant histiocytosis cells are atypical round cells that no longer resemble normal macrophages and display multiple criteria of malignancy[6]. Marked anisokaryosis is usually present. Phagocytosis of erythrocytes, neutrophils, and other tumor cells by both mononuclear and multinucleated tumor cells is also observed[7].

Immunohistochemical staining is useful to determine the lineage of the highly anaplastic round cells seen with canine MH/DHS[8].

Clinical outcome in dogs with MH/DHS reflects the aggressive behavior and poor prognosis of the neoplasm.

Chemotherapy with human major histocompatibility complex, or zoledronate in conjunction with cyclophosphamide, vincristine, doxorubicin and prednisolone may result in survival times ranging from several months to 6 years[9].


  1. Efforter VK, Moore PF (2002) Localized and disseminated histiocytic sarcoma of dendritic cell origin in dogs. Vet Pathol 39:74-83
  2. Withrow SJ, MacEwen EG (1996) Small Animal Clinical Oncology, 2nd ed. W B Saunders Co., Philadelphia. pp:279
  3. van Kuijk L et al (2013) Peri-articular Histiocytic Sarcoma and Previous Joint Disease in Bernese Mountain Dogs. J Vet Intern Med Mar 4
  4. Moore PF, Rosin A (1986) Malignant histiocytosis of Bernese Mountain Dogs. Vet Pathol 23:1-10
  5. Schmidt ML, et al (1993) Clinical and radiographic manifestations of canine malignant histiocytosis. Vet Quarterly '14:117-120
  6. Wellman SL, et al (1985) Malignant histiocytosis in four dogs. J Am Vet Med Assoc 187:919-921
  7. Rosin A, Moore P, Dubielzig R (1986) Malignant histiocytosis in Bernese Mountain Dogs. J Am Vet Med Assoc 188:1041-1045
  8. Ramirez S, Douglass JR, Robertson ID (2002) Ultrasonographic features of canine abdominal malignant histiocytosis. Vet Radiol Ultrasound 43:167-170
  9. Visonneau S, et al (1997) Successful treatment of canine malignant histiocytosis with the human major histocompatibility complex nonrestricted cytotoxic T-cell line TALL-104. Clin Cancer Res 3:1789-1797