What is the characteristic feature of myeloid metaplasia?

Myeloid Metaplasia: Characteristics and Features

Myeloid metaplasia results in extramedullary hematopoiesis, which is the formation of bone marrow elements outside of the medullary cavity. 1, 2

Key Characteristics of Myeloid Metaplasia

• Myeloid metaplasia is characterized by extramedullary hematopoiesis, most commonly occurring in the spleen and liver 3
• It is typically associated with significant splenomegaly, not rarely associated with it 4
• It affects predominantly older adults with a median age at diagnosis of 60 years, with more than 90% of patients diagnosed after age 40 years (not young females) 4
• It is characterized by increased bone marrow megakaryocytes, which are atypical and hyperplastic 5

Pathophysiology

• Myeloid metaplasia involves two pathogenetic processes:

  • A primary clonal hematopoietic stem cell disorder resulting in chronic myeloproliferation and atypical megakaryocytic hyperplasia 5
  • A secondary process of bone marrow fibrosis caused by non-clonal fibroblastic proliferation induced by growth factors abnormally released from clonal megakaryocytes 5

• The disease results in extramedullary hematopoiesis in various organs when bone marrow function is compromised 2, 3

Clinical Manifestations

• Massive splenomegaly is a hallmark feature 4
• Progressive anemia is common and contributes to morbidity 4
• Constitutional symptoms are often profound 4
• Extramedullary hematopoiesis can occur in various organs beyond the spleen and liver, including the lungs and pleura in some cases 3

Diagnostic Features

• Diagnosis is confirmed by bone marrow examination after ruling out other causes of myelofibrosis 4
• The presence of megakaryocytes admixed with other hematopoietic elements in extramedullary sites is a diagnostic feature 2
• Bone marrow typically shows substantial fibrosis 5

Prognosis and Treatment

• Median survival is approximately 5 years 4
• Poor prognostic factors include anemia (hemoglobin <10 g/dl), leukopenia or leukocytosis, circulating blasts, and hypercatabolic symptoms 4
• Conventional treatment is palliative and includes management of anemia with androgens, corticosteroids, or erythropoietin 4
• Symptomatic splenomegaly may require cytoreductive therapy or splenectomy 4

In summary, myeloid metaplasia is characterized by extramedullary hematopoiesis with increased and atypical bone marrow megakaryocytes. It predominantly affects older adults rather than young females and is typically associated with significant splenomegaly.