Acute radiation syndrome

Overview

Acute Radiation Syndrome (ARS), also known as radiation sickness, is a serious illness that occurs after the entire body or a significant portion of it is exposed to a high dose of ionizing radiation over a short period of time—typically within minutes. ARS can cause damage to multiple organ systems and is most commonly associated with nuclear accidents, radiation therapy mishaps, or radiological warfare. The severity of ARS depends on the dose, duration, and type of radiation exposure, and it progresses through defined clinical stages.

Causes

ARS is caused by exposure to a high dose of ionizing radiation (usually >1 Gray [Gy]) over a short duration. Common sources and scenarios include:

• Nuclear power plant accidents (e.g., Chernobyl, Fukushima)

• Detonation of nuclear weapons

• Radiological terrorism (dirty bombs)

• Improper handling of radioactive sources in industrial or medical settings

Ionizing radiation causes direct cellular damage and produces free radicals, leading to DNA injury, tissue necrosis, and disruption of rapidly dividing cells, especially in the bone marrow, gastrointestinal tract, and skin.

Symptoms

ARS develops in phases and the symptoms vary depending on the radiation dose:

1. Prodromal Stage (within hours):

• Nausea and vomiting

• Anorexia

• Fatigue

• Diarrhea (in higher doses)

2. Latent Stage (hours to days):

• Temporary improvement of symptoms

• Patient appears relatively well

3. Manifest Illness Stage:

Specific syndromes appear depending on the absorbed radiation dose:

• Hematopoietic Syndrome (1–6 Gy): Bone marrow failure, infection, bleeding, anemia

• Gastrointestinal Syndrome (6–30 Gy): Severe diarrhea, dehydration, electrolyte imbalance, sepsis

• Cerebrovascular Syndrome (>30 Gy): Seizures, confusion, ataxia, coma, and rapid death within hours to days

4. Recovery or Death:

Depending on dose, medical care, and organ damage. Survivors may experience long-term effects such as cancer or organ dysfunction.

Diagnosis

Diagnosis of ARS is based on history of radiation exposure, symptom progression, and laboratory findings. Steps include:

• Clinical history: Time, duration, and suspected dose of exposure

• Physical examination: Signs such as skin erythema, blisters, neurological changes

• Blood tests: Monitoring lymphocyte count decline (a sensitive early marker), neutropenia, and thrombocytopenia

• Cytogenetic analysis: Chromosomal aberration testing in lymphocytes for dose estimation

• Biodosimetry tools: When available, used for precise dose reconstruction

Treatment

There is no specific antidote for ARS, so treatment focuses on supportive care and managing complications. Key interventions include:

Supportive Care:

• Fluid and electrolyte replacement

• Antiemetics for nausea and vomiting

• Broad-spectrum antibiotics and antifungals to prevent infections

• Blood transfusions for anemia and thrombocytopenia

• Nutritional support

Hematopoietic Syndrome Management:

• Colony-stimulating factors (e.g., filgrastim) to stimulate white blood cell production

• Bone marrow transplant in select severe cases

Advanced Care:

• Intensive care for organ failure

• Skin grafts or wound care for radiation burns

• Psychological support

Prognosis

The prognosis for ARS depends largely on the radiation dose and speed of treatment. General outcomes by exposure level:

• <2 Gy: Mild symptoms, full recovery likely

• 2–6 Gy: Moderate to severe symptoms, recovery possible with intensive care

• 6–10 Gy: Life-threatening, high risk of complications, survival possible with aggressive treatment

• >10 Gy: Poor prognosis, high mortality even with treatment

Long-term survivors may be at increased risk for cancers, infertility, cataracts, and organ damage. Lifelong follow-up is often required.