Agnogenic Myeloid Metaplasia

Slides of agenogenic myeloid metaplasia include: Agnogenic Myeloid Metaplasia Agnogenic myeloid metaplasia (AMM, primary idiopathic myelofibrosis, myelosclerosis) is a clonal stem cell defect characterized by panmyelosis , progressive bone marrow fibrosis and splenomegaly. It usually appears in middle age to elderly individuals, and only rarely in younger people. There is an equal incidence of agnogenic myeloid metaplasia in males and females.

Patients with agnogenic myeloid metaplasia can appear relatively healthy for years. In later stages of the disease, however, patients present with fever, weight loss, and sweating. Anemia associated with agnogenic myeloid metaplasia can also result in fatigue and weakness. Physical examination will show splenomegaly, and gout due to hyperuricemia.

Peripheral blood findings show the following:

  • Variable Hgb, Hct with progressive anemia
  • Tear-drop red blood cells , normoblasts
  • Platelet count declines with progression of disease
  • Giant platelets
  • Circulating megakaryocytes
  • Varable leukocytosis (15-30 x 10^9/L)
  • Left shift (often 1-10% blasts)
  • Anemia
  • Basophilia/eosinophilia in about 10%

Fibrosis in agnogenic myeloid metaplasia makes bone marrow aspiration difficult. Bone marrow biopsy will show the following:

  • Initially hypercellular
  • Atypical megakaryocytic hyperplasia
  • Megakaryocytic pleomorphism (micro to hyperlobated)
  • Dilated sinusoids with intravascular hematopoiesis
  • Fibrotic phase: collagen fibrosis and loss of hematopoiesis except for megakaryocytes
  • Marked thickness of bone trabeculae (osteosclerosis)

The fibrosis in agnogenic myeloid metaplasia is a result in a defect in regulation, production and degradation of reticulin. Patients with agnogenic myeloid metaplasia will usually show increased reticulin, even in early stages of the disease. Acute leukemia, usually myeloid type ( AML ), develops in 10-20% of patients with agnogenic myeloid metaplasia. The megakaryocytic component is not unusual, and there are no distinctive chromosomal abnormalities. Median survival for patients with agnogenic myeloid metaplasia is 4-5 years.

 

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