Acute Leukemia
The broken factory — from the genetic glitch to the oncologic emergencies that make it a can’t-miss diagnosis.
The factory of life: normal hematopoiesis
Every blood cell descends from one multipotent stem cell, maturing as it divides. Leukemia is what happens when this orderly production line jams at the very first step.
Maturation is coupled to division. In acute leukemia, the myeloblast or lymphoblast is frozen at the blast stage — it divides but never grows up.
The architecture of the marrow
Healthy marrow balances active cellular islands with fatty spaces — cellularity is high at birth and falls with age. In leukemia it packs to nearly 100%, crowding out normal production. Toggle the marrow.
Balanced cellularity
Active hematopoietic islands nestle within fat cells, fed by sinusoids and the central vein.
~45% cellular · balanced
Diverse output
All lineages present and maturing — red cells, white cells, platelets released on schedule.
Packed with blasts
Cellularity approaches 100%. A monotonous sheet of immature clones fills the space.
~100% cellular · blasts
Production stops
Normal precursors are crowded out → the pancytopenia that brings the patient in.
The genetic glitch: the two-hit theory
A growth factor binds its receptor, signalling to the nucleus — where a mutation strikes. The damage splits two ways, and it takes both hits to make acute leukemia.
Hit 1 · Proliferation advantage
Division-promoting genes are stuck ON — cells divide uncontrollably.
Hit 2 · Maturation arrest
Differentiation genes are blocked — cells freeze at the blast stage.
Accumulation of immature, non-functional clones — cells that multiply endlessly but do no work.
Acute vs chronic
Both are proliferation gone wrong — but only acute leukemia also has maturation arrest. That single difference drives the entire clinical contrast. Toggle.
| Mechanism | Maturation arrest + proliferation — the blocked assembly line |
| Marrow | Packed with blasts (>20%); normal production stops |
| Clinical | Rapid marrow failure → pancytopenia |
| Timecourse | Aggressive — days to weeks |
| Mechanism | Proliferation advantage only — no arrest; the overactive factory |
| Marrow | Hypercellular but maturation continues |
| Clinical | Organomegaly (spleen / liver); often no initial failure |
| Timecourse | Indolent — months to years |
When the factory fails
Symptoms come from two directions at once: the absence of healthy cells, and the overcrowding of leukemic ones.
Marrow failure · pancytopenia
- Anemia → breathlessness, fatigue, pallor
- Neutropenia → infections, mouth ulcers, fever
- Thrombocytopenia → bleeding, bruising, petechiae
Tissue infiltration
- Deep bone pain (marrow expansion)
- Lymphadenopathy
- Hepatosplenomegaly
- Gum hypertrophy — specific to AML
Suspecting leukemia from the CBC
Do not be misled by the total WBC — it can be normal or low (aleukemic leukemia). The real clue is pancytopenia. Always read the differential: analysers miscount blasts as lymphocytes or monocytes.
Identifying the blast
On the smear, a healthy field is diverse. In leukemia it is monotonous — sheet after sheet of identical immature clones.
Features of the blast
- High nuclear-to-cytoplasmic ratio
- Prominent nucleoli (pale circles in the nucleus)
- Open, lacey chromatin
Auer rod — pathognomonic for AML.
The morphological hallmark
Monotony — the field is filled with one cell type. That uniformity is the diagnosis.
Immunophenotyping by flow cytometry
Morphology counts the blasts; flow cytometry names them. Diagnosis needs >20% blasts in the marrow, then a panel of CD markers to assign lineage. Pick a lineage.
Myeloid markers
Myeloperoxidase (MPO) positivity confirms the myeloid line.
B-lymphoid markers
T-lymphoid markers
Diagnosis rests on morphology (counting the blasts) and flow cytometry (naming them).
Red flags & emergencies
Time is critical — early recognition saves lives. Five ways acute leukemia can kill quickly.
Febrile neutropenia
Infection without defence — sepsis risk.
Tumor lysis
Metabolic overload from dying cells.
Hyperleukocytosis
WBC > 100k → leukostasis.
DIC
Bleeding & clotting — specific to APL (M3).
SVCO
Superior vena cava obstruction — T-cell ALL.
Tumor lysis & DIC
Tumor lysis syndrome
Massive cell death dumps intracellular contents: K⁺, phosphate, uric acid.
- Triad: hyperuricemia, hyperkalemia, hyperphosphatemia
- Risk: acute renal failure & arrhythmias
- Action: aggressive hydration, allopurinol, rasburicase
Disseminated intravascular coagulation
- High risk: acute promyelocytic leukemia (APL / M3)
- Signs: ecchymoses, IV-site bleeding, abnormal clotting screen
- Action: immediate blood-product support (FFP, cryoprecipitate, platelets)
Leukostasis & febrile neutropenia
Leukostasis
- Threshold: WBC > 100 ×10⁹/L
- Lung sludge → hypoxia · brain sludge → confusion/stroke · visual blurring
- Action: cytoreduction (hydroxyurea), leukapheresis
Febrile neutropenia
- Fever > 38 °C with neutrophils < 0.5
- Danger: inflammation signs are absent — no neutrophils to make them
Start broad-spectrum antibiotics immediately — do not wait for labs.
The treatment roadmap
Supportive care
Reverse isolation · transfuse platelets (>10k) · transfuse RBCs (Hb >8).
Induction therapy
Intensive chemotherapy — kill blasts & empty the marrow to achieve remission.
Consolidation
Eliminate residual disease — chemotherapy or allogeneic stem-cell transplant, chosen by cytogenetic risk.
Prognosis rests heavily on cytogenetics and molecular mutations.
Key takeaways
Suspect pancytopenia
All cell lines fail; the neutrophil count is almost always low.
Ignore total WBC
A normal total WBC does not rule out leukemia — read the differential.
The 20% rule
Diagnosis requires >20% blasts in the bone marrow.
Act fast
Identify emergencies — sepsis, lysis, bleeding — immediately.
Cure sometimes, care always
“While we focus on blasts, genes, and counts, we must never lose sight of the person behind the diagnosis. Compassion is as vital as chemotherapy.”
End of lecture.
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