Acute Radiation Syndromes
⚡ Acute Radiation Syndromes (ARS) occur when high-dose ionising radiation damages rapidly dividing cells. These include bone marrow precursors, gut epithelium, and germinal cells. Differentiated cells are less vulnerable, but the inability of stem cells to repopulate tissues leads to organ failure.
ARS progresses through four phases: prodromal → latency → manifest illness → recovery or death. The severity depends on the dose (Gray, Gy), dose rate, and tissue sensitivity.
🌀 Stages of ARS
- 🚨 Prodromal Stage:
Appears within minutes to days of exposure depending on dose.
- Symptoms: nausea 🤢, vomiting 🤮, diarrhoea 💩, anorexia, abdominal cramps, fatigue, dehydration.
- Onset: within minutes at >8 Gy; hours to days at lower exposures.
- Important: severity correlates with dose — brief, mild prodrome at lower doses vs. explosive onset at higher exposures.
- ⏳ Latency Period:
The patient may appear deceptively well for days–weeks.
- Duration depends on syndrome: 1–6 weeks in haematopoietic, ~5–7 days in GI, hours in cerebrovascular.
- Represents a temporary period before stem cell exhaustion manifests.
- 🩸 Haematopoietic Syndrome (3–9 Gy):
- Radiation kills bone marrow stem cells → aplastic marrow.
- Latent period ~4 weeks (reflects RBC/WBC lifespan before depletion).
- Symptoms: neutropenia → infections 🤒, thrombocytopenia → bleeding/bruising, anaemia, fever, sepsis, multi-organ failure.
- Prognosis: often fatal without bone marrow rescue; survival possible with antibiotics, transfusions, stem cell transplantation.
- 🍽️ Gastrointestinal Syndrome (≥8 Gy):
- Crypt stem cells in intestinal mucosa destroyed → villous atrophy, barrier loss.
- Latency ~7 days, then acute decompensation.
- Symptoms: severe vomiting, watery/bloody diarrhoea, abdominal cramps, electrolyte loss, sepsis from bacterial translocation.
- Death usually occurs 7–10 days post-exposure despite supportive therapy.
- 🧠 Cerebrovascular Syndrome (>20–30 Gy):
- Rapid onset, no true latency.
- Mechanism: capillary leak in CNS → cerebral oedema, raised ICP, seizures, coma.
- Symptoms: confusion, ataxia, seizures, cardiovascular collapse.
- Invariably fatal within 24–72 hrs.
🧪 Investigations
- Serial lymphocyte counts (fall within 24–48 hrs, dose-dependent).
- Bone marrow biopsy for aplasia.
- Electrolytes, renal function (dehydration, sepsis risk).
- Imaging: not specific, but CT may show bowel thickening or cerebral oedema in severe cases.
💊 Management Principles
- 🔒 Isolation & barrier nursing to reduce infection risk.
- 💉 Supportive: IV fluids, electrolyte correction, blood product transfusions.
- 💊 Antibiotics, antifungals, antivirals for immunosuppression.
- 🧬 Growth factors (G-CSF) or stem cell transplant for marrow recovery if feasible.
- 🚫 GI and CNS syndromes: mainly palliative, as survival is rare.
💡 Clinical Pearls
- 📉 Absolute lymphocyte count drop within 48 hrs = rough dose predictor.
- ⏳ Latent phase is misleading — patients may seem well before collapse.
- 🧬 Children are more vulnerable due to rapidly dividing tissues.
- 🛡️ UK emergency response: REPPIR 2019 regulations guide radiation incident planning.
- ☢️ Long-term survivors may develop cataracts, infertility, and increased cancer risk.
