Acute Radiation Syndrome (ARS), also known as radiation sickness, occurs after a person is exposed to a high dose of ionizing radiation over a short period. The syndrome unfolds in a series of stages, each with distinct symptoms and physiological effects. Understanding these stages helps medical professionals diagnose and manage the condition effectively.
The **first stage** is called the **prodromal stage**. This phase begins within minutes to a few days after exposure, depending on the radiation dose. During this time, the person experiences early symptoms such as nausea, vomiting, loss of appetite, fatigue, and sometimes diarrhea. These symptoms are the body’s immediate response to radiation damage, particularly affecting rapidly dividing cells in the gastrointestinal tract and other sensitive tissues. The severity and speed of onset of these symptoms correlate with the radiation dose—the higher the dose, the quicker and more intense the symptoms appear. For example, doses above 10 to 20 Gray (Gy) can cause symptoms within minutes. This stage can last from a few hours to several days.
Following the prodromal stage, the syndrome enters the **latent stage**. Despite the name, this phase is not symptom-free but is characterized by a deceptive improvement or disappearance of symptoms. The person may feel relatively well, and outward signs of illness may diminish. However, internally, radiation continues to damage critical systems, especially the bone marrow, gastrointestinal lining, and other organs. The length of the latent phase varies widely, from hours to weeks, depending on the dose and individual factors. This stage is dangerous because the absence of symptoms can mask the severity of internal damage.
The **third stage** is the **manifest illness stage**, where the true extent of radiation damage becomes evident. This phase involves the breakdown of one or more organ systems, leading to severe symptoms and complications. The specific symptoms depend on which organ systems are most affected and the radiation dose received. The three main clinical sub-syndromes of ARS during this stage are:
– **Hematopoietic syndrome** (bone marrow syndrome): Occurs at doses roughly between 1 and 10 Gy. Radiation destroys bone marrow cells responsible for producing blood cells, leading to a drop in white blood cells, red blood cells, and platelets. This causes increased susceptibility to infections, anemia, and bleeding. Symptoms include fever, weakness, bleeding gums, and infections. Without treatment, this syndrome can be fatal within weeks.
– **Gastrointestinal syndrome**: Occurs at doses above approximately 10 Gy. Radiation severely damages the lining of the stomach and intestines, causing nausea, vomiting, severe diarrhea, dehydration, electrolyte imbalance, and abdominal pain. The mucous membranes become ulcerated and bleed, leading to a high risk of infection and death within days to weeks.
– **Neurovascular syndrome**: Occurs at extremely high doses, generally above 20 to 30 Gy. This syndrome affects the central nervous system and cardiovascular system, causing confusion, seizures, loss of consciousness, severe hypotension, and rapid death, often within hours to days.
During the manifest illness stage, other symptoms may include skin damage such as redness, blistering, and peeling, as well as hair loss. The severity of these symptoms depends on the radiation dose and exposure area.
The **final stage** is the **recovery or death phase**. For those who survive the manifest illness stage, recovery can be prolonged and complicated. Recovery depends on the dose, the effectiveness of medical treatment, and the individual’s overall health. Bone marrow recovery is critical and may require interventions such as blood transfusions, antibiotics, and growth factors to stimulate blood cell production. Gastrointestinal damage may require intensive supportive care to manage fluid loss and prevent infections. In cases of very high exposure, multiple organ failure can occur, leading to death despite aggressive treatment.
Throughout these stages, the timing and severity of symptoms provide clues about the radiation dose received and the prognosis. For example, rapi
