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Syndromes
ARS is not a single syndrome but rather a series of sub-syndromes, each of which
evolves over time. The first syndrome involves the hematopoietic system, usually from
doses as low as 0.7 Gy. The GI system is affected next, followed by the cardiovascular
system and the CNS. These sub-syndromes are progressive and additive with increasing
dose, as each organ system is damaged in turn. The cardiovascular and CNS subsyndromes
are usually discussed together because both are rapidly lethal, caused by
microvascular injury, and without effective treatment.
Hematopoietic sub-syndrome. The hematopoietic system is affected at doses >0.7 Gy.
Although the dose range has been stated as 1–5 Gy, the hematopoietic system actually
begins to show damage at doses below 1 Gy, and damage continues at all higher doses.
The stem cells of all bone marrow cell lines are affected, so that all production of all
blood cells is reduced or stopped. The clinical severity increases with dose, with
ancytopenia occurring above about 2 Gy.
The prodrome begins 3–26 hours after doses of 1 to 5 Gy, lasting 48 hours or less. The
latent period is mostly asymptomatic, except for possible mild weakness, fatigue, and
anorexia that lasts 3–4 weeks. Hair loss (which requires about 3 Gy) and weight loss
appear at about day 14. The manifest illness phase sets in at 3–5 weeks, sooner at higher
doses. Bone marrow atrophy with pancytopenia (Figure 6.4) can lead to hemorrhage and
infection, similar to that which occurs in chemotherapy patients.
Uncomplicated cases can survive with treatment, which includes bone marrow
resuscitation and prevention of infections and hemorrhage. Marrow irradiated to 3 Gy
shows depletion of cells, which are replaced with fat. Many remaining cells undergo
pyknotic death or look grossly abnormal, containing large, bizarre nuclei.
Typical changes in the peripheral blood profile occurs as early as 24 hours after
irradiation. Figure 6.5 shows the pattern of blood counts over time after 3 Gy of
exposure. Lymphocyte levels fall immediately on day 1. At about 4 weeks, cell counts
are at their lowest. The depleted white cells and platelets predispose to hemorrhage and
overwhelming infection. Treatment is aimed at protecting patients from infection and
restoring blood-forming elements.
Gastrointestinal sub-syndrome. This sub-syndrome is also termed radiation enteropathy
and is seen occasionally in the setting of radiation oncology or among victims of a highdose
regional abdominal exposure. Major injury of the GI tract is clinically evident at
absorbed, whole-body doses of >5 Gy. The prognosis is grave at doses >6 Gy. Doses >8
Gy are generally lethal.
The prodrome begins abruptly in 1–4 hours (usually 1–2 hours), can last >48 hours, and
can be severe. The latent period is 5–7 days, with symptoms of malaise and weakness
severe enough to be disabling. The clinical course can be stormy during the manifest
illness phase, with complete paralytic ileus as the mucosa breaks down. This is marked
by abdominal distention, vomiting, diarrhea, and GI collapse. The damaged mucosa
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