Acute Myeloid Leukaemia in Children
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Direct answer
Acute myeloid leukaemia accounts for roughly 15 to 20 per cent of childhood leukaemia and behaves nothing like ALL: it presents at the extremes of childhood (infancy and adolescence), carries cytogenetic rather than age-based risk, and is treated with intensive cytarabine-anthracycline induction rather than long gentle lymphoid protocols. Auer rods on the smear, gum hypertrophy, chloromas and disseminated intravascular coagulation point to myeloid disease before any flow cytometer confirms it. The one subtype that changes everything is acute promyelocytic leukaemia (M3), where all-trans retinoic acid has converted the most fatal leukaemia into the most curable.
What you must remember
- Frequency ladder: ALL about 75–80 per cent of childhood leukaemia, AML 15–20 per cent; peak of AML in infancy and again in adolescence.
- Auer rods (eosinophilic needle-like inclusions) are pathognomonic of myeloid lineage; cytochemistry shows myeloperoxidase positivity in AML versus PAS block positivity in ALL.
- FAB subtypes M0–M7: gum hypertrophy and chloromas suggest M4/M5; M3 is acute promyelocytic leukaemia; M7 (megakaryoblastic) clusters with Down syndrome.
- Down syndrome children have a greatly raised risk of AML — transient abnormal myelopoiesis in the neonate (which resolves spontaneously) and later megakaryoblastic AML in the preschool years.
- APL (M3) presents with DIC and a low fibrinogen; ATRA plus arsenic trioxide, with blood product support, is the backbone of therapy — trans-retinoic acid must never be delayed for confirmatory tests in a bleeding patient.
- Hyperleucocytosis (above 100,000/cumm) risks leukostasis and tumour lysis: hydrate aggressively, allopurinol or rasburicase, and consider leukapheresis.
- Induction is the classic "7+3" — seven days of cytarabine plus three of an anthracycline — with intrathecal chemotherapy for CNS prophylaxis; complete remission is achieved in the large majority.
- Survival is markedly lower than ALL — of the order of 65–70 per cent in well-resourced settings — and haematopoietic stem cell transplantation is considered for high-risk or refractory disease.
- Bone marrow examination (morphology, cytochemistry, flow cytometry, cytogenetics) is the definitive investigation; the peripheral smear alone never starts therapy.
A typical exam case
A thirteen-year-old with three weeks of gum bleeding is found to have swollen, boggy gingivae, a tender bluish swelling over the clavicle and platelets of 18,000. The combination of gum hypertrophy (monocytic involvement, M4/M5) and a chloroma (granulocytic sarcoma) should make you write AML before the count comes back. The smear shows blasts with Auer rods; the marrow confirms AML with monocytic differentiation. Admit, transfuse platelets for bleeding, screen for DIC with fibrinogen and D-dimer, and start tumour lysis precautions.
The second case is the exam's trap-with-a-twist: a nine-year-old with pancytopenia and intractable bleeding from venepuncture sites, a fibrinogen of 80 mg/dL and smear promyelocytes with heavy granulation. That is APL with life-threatening DIC. Management is not a leisurely work-up — start ATRA immediately, give fresh frozen plasma, cryoprecipitate and platelets to keep fibrinogen and platelets above safe thresholds, add arsenic in standard-risk disease per current protocols, and watch for differentiation syndrome (fever, weight gain, pulmonary infiltrates) treated with dexamethasone and temporary ATRA hold. APL is also the one leukaemia where the coagulopathy kills before the blast count does, and where early death is almost always a failure to start ATRA early.
Where students slip
Candidates routinely import ALL logic into AML answers and lose marks. The classic slips: quoting a month of induction-phase steroids (steroids are not the backbone of AML therapy), treating risk by age and initial white count alone (in AML, cytogenetics — favourable core binding factor abnormalities versus unfavourable monosomy 7 or complex karyotype — drives risk), and forgetting the Down syndrome-myeloid relationship. A negative MDASH: remember also that WBC counts in AML can be low, normal or high — a normal count with blasts on smear still mandates a marrow. Finally, in any bleeding leukaemic child, check the fibrinogen before blaming thrombocytopenia; missing APL-associated DIC is the single most dangerous error in this topic.
Frequently asked questions
Which morphological finding is pathognomonic of myeloid lineage?
Auer rods, eosinophilic cytoplasmic inclusions of fused primary granules seen in blasts; cytochemical myeloperoxidase positivity supports the same lineage call.
How does acute promyelocytic leukaemia differ in emergency management?
It presents with DIC, so ATRA is started immediately along with aggressive correction of coagulopathy with plasma, cryoprecipitate and platelets; arsenic trioxide is combined with ATRA in standard-risk disease.
What is the relationship between Down syndrome and AML?
Children with Down syndrome have a markedly increased risk of megakaryoblastic AML in early childhood, and neonates with DS may show transient abnormal myelopoiesis that resolves spontaneously.
What induction regimen is standard for childhood AML?
Cytarabine infusion for seven days with an anthracycline for three ("7+3"), plus intrathecal chemotherapy, repeated induction or intensification blocks per protocol.
When is haematopoietic stem cell transplantation considered in AML?
For poor-risk cytogenetics, primary refractory disease or relapse, ideally in second remission, preferably with a matched family donor.