Anaphylactic Deaths

Most anaphylactic deaths seen by a medical examiner are caused by insect bites, drugs, or foods. The symptoms of anaphylactic attack are faintness, itching of the skin, urticaria, tightness in the chest, wheezing, respiratory difficulty, and collapse. In anaphylactic deaths, the onset of symptoms is usually immediate or within the first 15 to 20 min. Beyond that time, one would need a well-documented medical history of gradually developing symptoms to implicate an anaphylactic reaction, e.g., the development of itching or wheals and flares. Death usually occurs within 1 to 2 h. In some insects, e.g., fire ants, the venom is directly toxic and death can occur without anaphylactic reaction if there were a large number of bites.13 In such cases, death typically occurs after 24 h.

A fatal anaphylactic reaction results in acute respiratory distress or circulatory collapse. Obstruction of the upper airway can be caused by pharygeal or laryngeal edema; of the lower airway, by bronchospasm with contraction of the smooth muscle of the lungs, vasodilation, and increased capillary per-meability.14 Cardiac arrest may be caused by respiratory arrest; the direct effects of the chemical mediators of anaphylaxsis on the heart or shock caused by a combination of intravascular fluid loss from edema and vasodilatation. Pumphrey and Roberts studied 56 anaphylactic deaths coming to autopsy.15 They found that, in all 16 deaths that were caused by food allergy, there was difficulty in breathing, with death in 13 of the cases caused by respiratory arrest. In contrast, shock without any difficulty in breathing occurred in eight of 19 cases caused by insect venom and 12 of 21 caused by iatrogenic reactions.

At autopsy, the findings are often nonspecific. There is often laryngeal edema, but rarely complete obstruction of the airway. Pumphrey and Roberts reported larygeal or pharygeal edema in 8% and 49%, respectively, of individuals who died immediately.15 Emphysema caused by the bronchoconstriction might be present. Visceral and pulmonary congestion, edema, and pulmonary hemorrhage are present, but are nonspecific. In Pumphrey and Roberts' study, 23 of 56 anaphylactic deaths had no macroscopic findings at autopsy.

To make a diagnosis of an anaphylactic reaction, one needs either a history of an allergy or a witnessed collapse and death following an insect bite, ingestion of food, or administration of a drug. Most deaths attributed to therapeutic agents involve the administration of either penicillin or an iodine-containing contrast agent used for diagnostic purposes. Death, however, has been associated with a multitude of other therapeutic agents. The introduction of low-osmolar contrast agents in radiology should reduce the number of adverse and fatal reactions to iodinated contrast agents.

In death caused by an anaphylactic reaction to an insect bite, it is possible to detect elevated levels of venom-specific IgE antibodies in postmortem blood.13,15,16 Elevated levels of a specific IgE antibody do not necessarily indicate that an anaphylactic reaction took place, only that the individual is sensitive to the venom. The presence of such an antibody would be confirmatory evidence of an anaphylactic reaction caused by a sting from an insect. One percent of normal blood donors have been found to have elevated venom-specific IgE antibodies in their serum. Not all individuals dying of an anaphylactic reaction demonstrate antibodies to the specific insect that stung them. In such cases, a cross-reaction to antigens of another insect to which the deceased is allergic is suspected.

When IgE interacts with specific antigens, mast cells are activated, releasing a number of potent chemical mediators, including beta tryptase and histamine, from secretory granules in the cells. The level of tryptase rises rapidly, becoming detectible within 30 min, with peak concentrations reached in the first 2-3 h. Half-life of tryptase is 2 h. Resting mast cells secrete alpha tryptase. In mastocytosis, blood levels are raised. Anaphylaxis-like reactions in individuals with mastocytosis might not require IgE antibodies. Both IgE and tryptase can be measured in postmortem blood.

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