**Acute radiation sickness (ARS) and chronic radiation sickness (CRS) are two distinct conditions caused by exposure to ionizing radiation, differing primarily in the dose, duration of exposure, onset of symptoms, and clinical manifestations.**
Acute radiation sickness occurs after a *high dose* of radiation is absorbed in a *short period*, typically minutes to hours. This rapid, intense exposure overwhelms the body’s ability to repair damage, leading to a sudden onset of symptoms. In contrast, chronic radiation sickness results from *lower doses* of radiation absorbed *gradually* over weeks, months, or even years, allowing some biological repair but causing cumulative damage.
### Exposure and Dose Differences
– **Acute Radiation Sickness (ARS):** Usually involves a total body dose exceeding about 0.7 Gray (Gy) delivered within minutes. The severity increases with dose, with doses above 6 Gy causing severe symptoms and doses above 10 Gy often fatal. Exposure sources include nuclear accidents, radiation therapy accidents, or nuclear explosions.
– **Chronic Radiation Sickness (CRS):** Results from prolonged exposure to lower doses, often below the threshold for ARS but accumulating over time. This can happen in occupational settings like nuclear industry workers or people living in contaminated areas.
### Onset and Progression of Symptoms
– **ARS:** Symptoms appear quickly, often within minutes to hours after exposure. The illness typically progresses through stages:
1. **Prodromal phase:** Nausea, vomiting, headache, fatigue, and sometimes fever occur within hours.
2. **Latent phase:** Symptoms may temporarily improve or disappear for hours to weeks.
3. **Manifest illness phase:** Depending on dose and affected organ systems, symptoms reappear and worsen, including severe diarrhea, bleeding, infections, neurological symptoms, and potentially death.
4. **Recovery or death:** Recovery depends on dose and medical intervention; death can occur within days to weeks at high doses.
– **CRS:** Symptoms develop slowly and insidiously over months or years. Early signs include general weakness, fatigue, loss of appetite, and mild anemia. As exposure continues, more severe effects such as chronic infections, skin changes, and neurological symptoms may develop. The progression is gradual, often with fluctuating symptoms.
### Affected Body Systems and Symptoms
– **ARS:** The rapidly dividing cells are most vulnerable, especially in the bone marrow, gastrointestinal (GI) tract, and central nervous system (CNS).
– *Bone marrow syndrome* (0.7 to 10 Gy): Causes a drop in blood cells leading to infections, bleeding, and anemia.
– *Gastrointestinal syndrome* (6 to 10 Gy): Severe nausea, vomiting, diarrhea, dehydration, and electrolyte imbalance.
– *Neurovascular syndrome* (above 20-30 Gy): Confusion, loss of consciousness, seizures, and death within days due to brain edema and circulatory collapse.
– **CRS:** Chronic exposure damages multiple systems slowly:
– Blood-forming organs show persistent but less severe suppression, causing anemia and immune deficiency.
– Skin may develop chronic dermatitis, pigmentation changes, ulcers, and increased cancer risk.
– Nervous system symptoms include memory loss, headaches, and peripheral neuropathy.
– Other organs may show fibrosis and functional decline over time.
### Pathophysiology
– **ARS:** High-dose radiation causes immediate DNA damage, cell death, and inflammation. The damage to endothelial cells leads to vascular injury and tissue necrosis. The rapid cell loss in bone marrow and GI tract impairs critical functions, causing systemic failure.
– **CRS:** Repeated low-dose exposure causes cumulative DNA damage and oxidative stress. The body attempts repair but eventually accumulates mutations and cell dysfunction. Chronic inflammation and fi