Myelofibrosis (myeloid metaplasia, myelosclerosis) is a disorder of bone where the marrow is replaced by scar (fibrous) tissue, due to a proliferative response by bone-marrow fibroblasts.
Myelofibrosis has been classified in human medicine as either primary or secondary depending on the underlying etiology, but only secondary myelofibrosis has been reported in the dog.
Causes of myelofibrosis in dogs include, in order of importance:
- Long-term drug exposure - phenobarbital, phenytoin, phenylbutazone and colchicine
- Immune-mediated hemolytic anemia
- Neoplasia - leukemia, lymphoma, mammary tumors, multiple myeloma, malignant histiocytosis, gastrinoma, mast cell tumor
- Systemic inflammatory diseases - pyometra, pancreatitis, hepatitis, glomerulonephritis
- Immune-mediated thrombocytopenia
- Pyruvate kinase deficiency
- Myelodysplasia syndrome
- Breed predisposition - severe nonregenerative macrocytic hypochromic anemia in pregnant female Beagles
- Whole body γ-radiation
Diagnosis requires multiple bone marrow core biopsies and histological examination of other organ tissue samples, confirming the increased presence of fibrosis within bone marrow spaces and increased extramedullary hematopoiesis in other organs such as the liver and spleen.
In severely anemic dogs, whole blood transfusions of fresh frozen plasma may be required as a palliative strategy to forestall a demise.
Development of new protein kinase inhibitors has shown promise at treating myelofibrosis secondary to lymphoma.
- Weiss DJ (2008) Bone marrow pathology in dogs and cats with non-regenerative immune-mediated haemolytic anaemia and pure red cell aplasia. J Comp Pathol 138(1):46-53
- Mylonakis ME et al (2010) Absence of myelofibrosis in dogs with myelosuppression induced by Ehrlichia canis infection. J Comp Pathol 142(4):328-331
- Reagan WJ (1993) A review of myelofibrosis in dogs. Toxicol Pathol 21(2):164-169
- Weiss DJ (2005) Bone marrow necrosis in dogs: 34 cases (1996-2004). J Am Vet Med Assoc 227(2):263-267
- Weiss DJ & Smith SA (2002) A retrospective study of 19 cases of canine myelofibrosis. J Vet Intern Med 16(2):174-178
- Auler P et al (2011) Myeloid metaplasia in canine mixed mammary tumors: occurrence and characterization. Vet Q 31(4):173-177
- English RV et al (1988) Zollinger-Ellison syndrome and myelofibrosis in a dog. J Am Vet Med Assoc 192:1430-1434
- Weiss DJ (2006) A retrospective study of the incidence and the classification of bone marrow disorders in the dog at a veterinary teaching hospital (1996-2004). J Vet Intern Med 20(4):955-961
- Weiss DJ (2005) Sideroblastic anemia in 7 dogs (1996-2002). J Vet Intern Med 19(3):325-328
- Weiss DJ & Aird B (2001) Cytologic evaluation of primary and secondary myelodysplastic syndromes in the dog. Vet Clin Pathol 30(2):67-75
- Harvey JW (2006) Pathogenesis, laboratory diagnosis, and clinical implications of erythrocyte enzyme deficiencies in dogs, cats, and horses. Vet Clin Pathol 35(2):144-156
- Seed TM et al (1982) The ultrastructure of radiation-induced endosteal myelofibrosis in the dog. Scanning Electron Microsc 1:377-391
- William AD et al (2011) Discovery of the macrocycle 11-(2-pyrrolidin-1-yl-ethoxy)-14,19-dioxa-5,7,26-triaza-tetracyclo[188.8.131.52(2,6).1(8,12)]heptacosa-1(25),2(26),3,5,8,10,12(27),16,21,23-decaene (SB1518), a potent Janus kinase 2/fms-like tyrosine kinase-3 (JAK2/FLT3) inhibitor for the treatment of myelofibrosis and lymphoma. J Med Chem 54(13):4638-4658