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Anaphylaxis (also known as anaphylactic shock or reaction) is an acute severe systemic type I hypersensitivity reaction, commonly presenting with urticaria/angioedema, hypotension and bronchial hyperreactivity. It may be fatal.
Anaphylactoid reactions result from non-immune system mediated mechanisms. However they are clinically indistinguishable from anaphylactic reactions with similar risks of multiorgan failure and death. In practical terms the distinction between anaphylactic and anaphylactoid reactions is academic as clinically they are managed identically 5.
The published epidemiological data from the USA, UK and Australia, demonstrates an incidence rate of anaphylaxis of 7 to 50 cases per 100,000 per annum. The number of deaths is estimated to be up to 3 per 1,000,000 per year.
There is no gender preference in adults; in prepubescent children, it is more common in boys 1.
In the USA, in the two decades up to 2019, almost 50,000 cases of anaphylaxis occurred; of these, ~6% were fatal 8.
The drugs most commonly triggering anaphylaxis overall were 8:
- monoclonal antibodies
However, the agents most likely to cause a fatal anaphylaxis were 8:
- iodinated contrast media
- perioperative drugs
The typical presentation affects the skin, chest, GI tract and cardiovascular system. Often the signs and symptoms are indolent in onset and initially mild, such as itching and rashes.
- systemic hypotension
However, up to 20% patients with anaphylaxis lack any evidence of circulatory compromise or dermatological sequelae 2.
In radiology, approximately 1 in 40,000 patients will experience anaphylaxis from iodinated contrast media. Most anaphylaxis will occur within twenty minutes of administration of IV contrast agents, although longer delays are occasionally seen.
Radiological features may includes signs of angioedema involving the face, tongue, lips and larynx - which usually appears as diffuse transpatial edema with circumferential mucosal thickening 7. Airway narrowing may also be evident. In practice, most clinicians in most situations should act to treat this situation immediately, with imaging after treatment.
Treatment and prognosis
Treatment protocols may vary by institution, however usually involve the administration of epinephrine and oxygen with measures to protect the patient's airway if necessary. Although fatal outcomes happen, they are rare with proper treatment 6.
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