Ch04: Haematology — Anaemia & Leukaemia

Preparatory Mindset

Childhood haematology in this syllabus covers iron-deficiency anaemia (IDA — the most common anaemia of childhood), megaloblastic anaemia (B12/folate), and acute leukaemia (mostly ALL). The mindset:

• Anaemia workup starts with MCV: microcytic (iron deficiency, thalassaemia, chronic disease, sideroblastic) → normocytic (bleeding, haemolysis, aplasia) → macrocytic (B12/folate, hypothyroidism) — with reticulocytes separating production from destruction.
• IDA: microcytic hypochromic, low ferritin, ↑ red cell distribution width, pale child, pica, koilonychia — from inadequate dietary iron (cow's milk <1 yr, exclusive breastfeeding past 6 mo) → oral iron, dietary advice, repeat FBC in 4-6 weeks; refractory → investigate (malabsorption, occult loss, thalassaemia trait).
• Acute leukaemia (ALL most common in children): fever + pallor + bleeding + bone pain + lymphadenopathy/hepatosplenomegaly → pancytopenia + blasts on film → bone marrow aspirate (blast count) is diagnostic → chemotherapy (not surgery); ALL is highly curable (>90% in children).

The exam pearl: "child with pallor + pica" = IDA; "child with bone pain + bruising + fever" = leukaemia.

Core Concepts

1. Anaemia — classification by MCV and reticulocyte

Blood film patterns: IDA — small pale RBCs with increased central pallor, anisopoikilocytosis; megaloblastic — macro-ovalocytes + hypersegmented neutrophils; thalassaemia — target cells, microcytosis with normal RDW.

Initial workup (any anaemia): Hb, Hct, MCV/MCH/MCHC, WBC + differential, platelet count, reticulocyte count, blood film — then targeted tests (ferritin, B12/folate, Hb electrophoresis, DAT, Coombs).

2. Iron-deficiency anaemia (IDA)

Why so common: rapid growth + expanding blood volume; inadequate dietary iron — exclusive breastfeeding past 6 months without weaning iron, cow's milk before 1 year (low iron + poor absorption + occult GI loss), poor weaning solids; premature infants (low stores).

Clinical: pallor, fatigue, irritability, poor appetite, pica (eating dirt/ice), koilonychia (spoon nails), tachycardia, systolic murmur; severe — breathlessness, heart failure; behavioural/cognitive effects (long-term with chronic deficiency).

Investigations:

Management:

1. Oral iron (ferrous sulphate 3-6 mg/kg/day elemental) — for 3 months (1 month to normalise Hb + 2 months to replenish stores).
2. Dietary advice — iron-rich weaning foods (fortified cereal, meat, egg, legumes), vitamin C enhances absorption (orange juice), avoid tea with meals (tannins ↓ absorption); no cow's milk before 1 year; limit milk after.
3. Response check: reticulocyte rise by 3-7 days, Hb rise ≥10-20 g/L in 2-4 weeks — if no response: compliance? wrong diagnosis (thalassaemia trait), ongoing loss (occult GI bleed), malabsorption → investigate.
4. Severe/symptomatic or non-absorbing: IV iron; transfusion only if severe/acute compromise.

Differential — thalassaemia trait (common in Chinese/Mediterranean): mild microcytic anaemia, normal/increased ferritin, normal RDW, elevated HbA2 (on electrophoresis); do NOT give iron (no deficiency). This is the classic "IDA that doesn't respond" in Chinese children.

3. Megaloblastic anaemia (B12 / folate deficiency)

• Causes: folate — poor diet, malabsorption, anticonvulsants (phenytoin), haemolytic states; B12 — pernicious anaemia (rare in children), vegan diet, ileal disease (Crohn), congenital B12 defects, fish tapeworm, nitrous oxide.
• Clinical: pallor + glossitis (sore tongue), diarrhoea, neurological (B12 — subacute combined degeneration: paraesthesia, ataxia, vibration loss), mild jaundice (ineffective erythropoiesis).
• Investigations: macrocytic (MCV >100), hypersegmented neutrophils, ↓ B12 or ↓ folate (check both + red cell folate), ↑ LDH, ↑ indirect bilirubin; normal reticulocyte.
• Management: B12 replacement (IM hydroxocobalamin) for B12 deficiency (correct neurological damage); folic acid (oral) for folate deficiency; check B12 BEFORE giving folate alone (folate can mask B12 deficiency and worsen neurology); dietary correction; treat cause.

4. Acute leukaemia (ALL — the paediatric leukaemia)

Epidemiology: ALL is the most common childhood cancer (peak 2-5 years); AML less common (more in adolescents/infants).

Clinical — the "leukaemia syndrome":

• Bone marrow failure: fever (infection), pallor/fatigue (anaemia), bruising/petechiae/bleeding (thrombocytopenia) — the classic triad
• Infiltrative: bone pain/limping (periosteal infiltration — a big clue), lymphadenopathy, hepatosplenomegaly, gum hypertrophy (M4/M5 AML)
• CNS: headache, vomiting, cranial nerve palsy (leptomeningeal)
• Mediastinal mass (T-cell ALL) — superior vena cava syndrome, wheeze

Investigations:

Management (chemotherapy, NOT surgery):

1. Supportive care first: infection prophylaxis (empiric antibiotics for fever + neutropenia), tumour lysis syndrome prevention (hydration, allopurinol/rasburicase, monitor K/PO4/Ca/urate), blood products.
2. Multi-phase chemotherapy: induction (remission) → consolidation → maintenance (with intrathecal methotrexate for CNS prophylaxis; cranial irradiation now limited — neurotoxicity).
3. High-risk/relapse: allogeneic stem cell transplant (HSCT).
4. Prognosis: ALL cure >85-90% in children (favourable: age 1-10, low WBC, hyperdiploidy; unfavourable: infant, high WBC, Philadelphia chromosome, CNS disease).

Complications of treatment: neutropenic sepsis, tumour lysis syndrome, mucositis, cardiomyopathy (anthracyclines), secondary malignancy, growth/endocrine (cranial RT), fertility issues — long-term follow-up.

High-Yield Points

Topic Summary

Childhood anaemia is classified by MCV: IDA (microcytic, low ferritin, ↑RDW — treat with oral iron 3 months + diet; thalassaemia trait mimics but has normal ferritin/↑HbA2), megaloblastic (macrocytic, B12/folate — check B12 first), normocytic (bleeding/haemolysis). Acute leukaemia (ALL) presents with fever + pallor + bruising + bone pain + organomegaly; pancytopenia + blasts → bone marrow aspirate (>20-25% blasts) is diagnostic; treatment is chemotherapy (with tumour lysis prevention); childhood ALL is curable in >85-90%.