What is the characteristic bone‑marrow finding in a child diagnosed with immune thrombocytopenia (ITP)?

Bone Marrow Findings in Pediatric Immune Thrombocytopenia (ITP)

The characteristic bone marrow finding in a child with ITP is increased megakaryocytes (megakaryopoiesis), not decreased platelets, abnormally shaped precursors, or fibrosis. 1

Understanding the Bone Marrow in ITP

The Hallmark Finding: Increased Megakaryocytes

• ITP is characterized by normal or increased numbers of megakaryocytes in the bone marrow, reflecting a compensatory response to peripheral platelet destruction. 1

• The bone marrow demonstrates overproliferation of megakaryocytes in most ITP patients, with normal morphology and maturation patterns. 2

• Megakaryocytes appear normal in size and morphology, though they may be slightly increased in number compared to age-matched controls. 2, 3

Why the Other Options Are Incorrect

Decreased number of platelets is seen in the peripheral blood, not the bone marrow examination itself—the marrow shows increased megakaryocyte production attempting to compensate. 1, 2

Presence of abnormally shaped precursor blood cells would suggest alternative diagnoses such as myelodysplastic syndrome (MDS), aplastic anemia, or leukemia—not typical ITP. 1, 2

Fibrosis of the bone marrow is not a feature of ITP and would indicate myelofibrosis or other bone marrow pathology requiring different management. 1

Critical Clinical Context: When Bone Marrow Examination Is Actually Needed

The Modern Standard: Bone Marrow Is Usually NOT Required

• The American Society of Hematology strongly recommends against routine bone marrow examination in children with typical ITP features (Grade 1B recommendation). 1

• Diagnosis relies on careful history, physical examination, complete blood count, and peripheral blood smear review—these are sufficient in typical cases. 1

• A retrospective study of 332 children with typical ITP features found no cases of acute leukemia and only one case of bone marrow aplasia, confirming the safety of omitting bone marrow examination in typical presentations. 1

Red Flags That DO Require Bone Marrow Examination

Bone marrow examination becomes mandatory when atypical features are present: 1

• Fever, bone pain, or joint pain
• Family history of thrombocytopenia or easy bruising
• Skeletal or soft-tissue morphologic abnormalities
• Non-petechial rash
• Lymphadenopathy or splenomegaly (spleen palpable in only ~12% of children with ITP, and when present suggests alternative diagnosis) 1, 4
• Abnormal hemoglobin level, white blood cell count, or white cell morphology
• Minimal or no response to first-line therapies (IVIg, corticosteroids) 1

Bone Marrow Is Also NOT Required Before Treatment

• Bone marrow examination is not necessary before initiating corticosteroids (Grade 2C recommendation). 1

• Bone marrow examination is not necessary in children who fail IVIg therapy (Grade 1B recommendation). 1

• Bone marrow examination is not necessary before splenectomy in children with typical features (Grade 2C recommendation). 1

Distinguishing ITP from Other Causes of Thrombocytopenia by Bone Marrow Findings

ITP vs. Aplastic Anemia

• Aplastic anemia shows markedly decreased megakaryocytes with reduced CFU-MK and BFU-MK colony formation rates, the opposite of ITP. 2

• Aplastic anemia presents with pancytopenia (low red cells, white cells, and platelets), not isolated thrombocytopenia. 1, 5

ITP vs. Myelodysplastic Syndrome (MDS)

• MDS demonstrates increased micromegakaryocytes with abnormal morphology (type I lymphoid small micromegakaryocytes) and dysplastic features. 2

• MDS shows two clones of megakaryocytes: pathologic micromegakaryocytes and normal precursors, with decreased BFU-MK formation. 2

ITP vs. Leukemia

• Leukemia presents with abnormal white blood cell count or morphology on peripheral smear, prompting bone marrow examination. 1, 5

• In a study of 127 children with presumed ITP, bone marrow examination led to a different diagnosis in only 5 patients (3.9%), and none had leukemia—all had atypical clinical or laboratory features at presentation. 5

The Pathophysiology Behind Increased Megakaryocytes

• ITP is an autoimmune disorder with antibody-mediated peripheral platelet destruction, not a bone marrow production problem. 1

• The bone marrow responds appropriately by increasing megakaryocyte production to compensate for shortened platelet survival in the periphery. 2, 6

• However, newer evidence suggests that platelet production may also be impaired in some ITP patients despite increased megakaryocyte numbers, challenging the traditional model. 1

Common Pitfalls to Avoid

Ordering bone marrow examination in every child with thrombocytopenia—this exposes children to unnecessary procedural risk and does not change management in typical ITP. 1, 5

Assuming decreased platelets in peripheral blood means decreased megakaryocytes in bone marrow—ITP shows the opposite pattern due to peripheral destruction. 2, 6

Missing atypical features that mandate bone marrow examination—splenomegaly, abnormal CBC parameters beyond thrombocytopenia, or systemic symptoms require further investigation. 1

Confusing bone marrow findings with peripheral blood findings—the question asks about bone marrow examination, where increased megakaryocytes are the hallmark, not decreased platelets. 1, 2