Acute radiation syndrome

Acute radiation syndrome, also known as radiation poisoning or radiation sickness, refers to the signs and symptoms associated with the acute effects of high-dose rates of ionizing radiation (usually over 0.5 Gy) through either whole body or partial body irradiation. 

Epidemiology

The exact prevalence of the condition is difficult to establish but people exposed to higher radiation doses and higher dose rates are at the highest risk.

High-risk situations include:

• radiation therapy 
• nuclear power plant accidents
• nuclear or radiological weapons use
• exposure to orphan sources

Clinical presentation

The syndrome has a number of phases:

• prodromal phase: symptoms are non-specific but can include: anorexia, diarrhea, fever, erythema of the skin, nausea, vomiting and headache. This usually appears 1-3 days after exposure. Lymphopenia is an early sign on blood tests.
• latent phase: with an apparent improvement in symptoms and may last hours or weeks.
• symptomatic phase: with a number of possible sub-syndromes occurring such as:
  • hematopoietic symptoms (1-8 Gy): infection, hemorrhage
  • gastrointestinal symptoms (5-20 Gy): diarrhea, electrolyte and fluid disturbances, gastrointestinal bleeding and perforation
  • neurovascular symptoms (>20 Gy): headache, focal neurological deficits, altered level of consciousness
• final phase: either recovery or death depending on the total dose and dose rate received

Pathology

A variety of factors must be considered when dealing with radiation exposure including the:

• dose
• route of exposure (e.g. external irradiation versus ingestion)
• area of the body exposed
• dose rate

Radiation-induced cytotoxicity causes many of the symptoms of the syndrome together with the inflammatory SIRS-like response to the large degree of cell death. More rapidly proliferating tissues (e.g. skin, bone marrow) are the most affected.

In the hematopoietic syndrome, white blood cells and platelets are lost predisposing to infection and hemorrhage, which are the most common form of death. In the gastrointestinal syndrome damage to the mucosal cells results in diarrhea, electrolyte and fluid loss and predisposes to bleeding and perforation. Damage to endothelial cells in the brain is thought to lead to vasogenic edema and potentially neurological symptoms at high enough doses.