With spring approaching people are often eager to get outside to enjoy the sunshine. Unfortunately, the warmer weather also brings with it a few unwanted guests. As people emerge from their homes, so do the stinging insects including fire ants, bees, wasps, hornets, and yellow-jackets. Since humans live in close proximity to the habitat of these members of the order Hymenoptera, they may find themselves meeting more often than they would like. While most people consider these interactions to be merely unpleasant, in the case of a person who has developed hypersensitivity to their venom they may become life-threatening. As a result, physicians must know how to diagnose and treat these reactions in a timely manner. A review of the management of hymenoptera stings is presented in one of the recent articles recommended by the American Board of Emergency Medicine in the Lifelong Learning and Self Assessment series. In this article, entitled Hypersensitivity to Hymenoptera Stings, Dr. Theodore M. Freeman discusses the most recent guidelines set forth by the American Academy of Allergy, Asthma, and Immunology and the American College of Allergy, Asthma, and Immunology.
A localized reaction is most common after hymenoptera stings, secondary to vasoactive components of their venom. The redness, swelling, and tenderness of the affected area usually resolves within forty-eight hours but can sometimes persist for up to a week. These self-limited reactions may result in considerable morbidity if they occur on the hands, feet, or near the eyes but they are not usually deadly. In fact, a 70-kg nonallergic adult would require about 1500 stings to receive a lethal dose of venom. They can, however, pose a significant risk of mortality if the sting occurs near or within the oral cavity, in which case the airway can become compromised. The most concerning reaction to a sting from hymenoptera is when the patient has developed IgE mediated immunity from a previous sting, resulting in a hypersensitivity reaction. Once a person develops the specific IgE antibodies to certain venom components, one sting is enough to produce anaphylaxis and death. Hypersensitivity reactions may be limited to cutaneous effects such as pruritis, urticaria, and angioedema. On the other hand, reactions may produce more systemic effects leading to much greater morbidity and even mortality. The gastrointestinal system may be involved causing a metallic taste, nausea, vomiting, diarrhea, and abdominal cramping. Toxic effects on the nervous system can produce a sense of impending doom, light-headedness, and dizziness. Reactions involving the pulmonary and cardiovascular systems can lead to breathing difficulties, bronchospasm, hypotension, and dysrhythmias.
Given the fact that it would be highly unethical to develop random controlled trials to study such a deadly process, most current treatment recommendations are based on anecdotal evidence. Local reactions can be treated symptomatically with cold compresses, nonsteroidal anti-inflammatory agents, and antihistamines. Topical antihistamines and corticosteroids can also be helpful. If a reaction area is large or involves hands, feet or eyes an oral steroid may also be added to the regimen. Systemic reactions involving anything more than the skin should be treated with intramuscular epinephrine, 0.01 mg per kilogram of body weight (maximum dose 0.3 mg for children and 0.5 mg for adults). Studies suggest that a delay or failure to administer epinephrine increases the chance of a fatal outcome. Even if the initial symptoms seem benign, subjective symptoms may progress rapidly to life-threatening effects. The fear of causing adverse effects on the cardiovascular system is far outweighed by the risk of death of the patient. According to the article, anaphylaxis itself has been associated with coronary vasospasm. Other treatment modalities may include supplemental oxygen, beta-agonists for bronchospasm, and intravenous fluids for hypotension. Definitive support for steroids is lacking but they are still sometimes given for reactions.
The decision of whether to admit patients to the hospital for continued treatment or observation after a reaction is not discussed in the article. While there are no hard and fast rules, according to _____, admission should be considered if the patient requires more than one dose of epinephrine. Observation might also be considered if the sting or reaction involves the oropharynx and there is concern that the patient’s airway may become compromised. An important concept to remember is that the risk of anaphylaxis with any event is dependent on the severity of the patient’s previous reactions. If the patient is to be sent home, the American Academy of Allergy, Asthma, and Immunology and the American College of Allergy, Asthma, and Immunology have provided guidelines for physicians to follow. Once the initial event is under control, the most important modifying factor for the patient is prevention of future stings. However, completely avoiding future stings is not always possible and therefore epinephrine auto-injectors should be prescribed for any patient who has had an anaphylactic reaction to a hymenoptera sting. Remember to instruct patients how and when to use the auto-injector and also advise them to seek medical care after use even if the symptoms resolve. There have been cases of death when symptoms initially resolved after the use of auto-injectors and patients did not seek medical care.
Since complete avoidance of potential contact with hymenoptera is often unavoidable, referral to an allergist for skin testing and possible immunotherapy is warranted in patients who have had an anaphylactic reaction. Sometimes it is difficult to determine whether a true anaphylactic reaction has occurred since anxiety symptoms related to the sting can mimic hypersensitivity symptoms. However, if patients are concerned enough to seek medical care, that in itself is reason to refer them to an allergist for testing. The allergist will conduct skin testing for specific IgE antibodies to the various hymenoptera, usually four to six weeks after the inciting event. The wait is to reduce false negative skin tests due to depletion of the anaphylactic mediators. Immunotherapy with hymenoptera venom, designed to desensitize patients to the allergen, is then recommended for patients with a history of anaphylaxis after a sting or suspected sting and who also have specific IgE antibodies. This therapy has been shown to significantly reduce future anaphylactic reactions. The treatment course typically consists of a build up of venom introduced to patients over a three to six month period until they reach a maintenance dose of approximately twice that of what a typical sting would deliver. Once the maintenance dose is reached the injections are then given once a month to once every two months, depending on the individual patient. Currently, the optimal length of continued maintenance immunotherapy has yet to be determined, with recommendations varying from three to five years to indefinitely. Please refer to Dr. Freeman’s article for more information about how the actual skin testing and immunotherapy is performed.
Dr. Freeman gives an excellent overview of the management of hymenoptera
stings. For more detail, be sure to read his article in the New England Journal
of Medicine, but until then there are few key points to remember. First of all,
epinephrine is the definitive treatment for any patient who presents with more
than cutaneous findings during a reaction. The risk of mortality from
anaphylaxis far outweighs any possible adverse effects on the heart. Other
treatment modalities to consider include antihistamines, oxygen,
bronchodilators, and intravenous fluids, when appropriate. Also, if the decision
is made to send patients home after a systemic reaction, refer them to an
allergist for skin testing and possible immunotherapy. Remember to prescribe
epinephrine auto-injectors and instruct them on appropriate use, stressing that
they should seek medical care even if symptoms resolve. Another recommendation
to give patients is that medical alert bracelets should be considered to alert
bystanders and health care professionals of their potential deadly allergy.
Theodore M Freeman, M.D. New England Journal of Medicine. Volume
351:1978-1984. November 4, 2004, Number 19
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