Rarely very low blood pressure may be the only sign of anaphylaxis.Coronary artery spasm may occur with subsequent myocardial infarction, dysrhythmia, or cardiac arrest. Those with underlying coronary disease are at greater risk of cardiac effects from anaphylaxis. The coronary spasm is related to the presence of histamine-releasing cells in the heart. Other
Gastrointestinal symptoms may include severe crampy abdominal pain, diarrhea, and vomiting. There may be confusion, a loss of bladder control or pelvic pain similar to that of uterine cramps. Dilation of blood vessels around the brain may cause headaches. A feeling of anxiety or of "impending doom" has also been described. Causes
Anaphylaxis can occur in response to almost any foreign substance. Common triggers include venom from insect bites or stings, foods, and medication. Foods are the most common trigger in children and young adults, while medications and insect bites and stings are more common in older adults. Less common causes include: physical factors, biological agents such as semen, latex, hormonal changes, food additives and colors, and topical medications. Physical factors such as exercise (known as exercise-induced anaphylaxis) or temperature (either hot or cold) may also act as triggers through their direct effects on mast cells. Events caused by exercise are frequently associated with cofactors such as the ingestion of certain foods or taking an NSAID. In aspirin-exacerbated respiratory disease (AERD), alcohol is a common trigger. During anesthesia, neuromuscular blocking agents, antibiotics, and latex are the most common causes. The cause remains unknown in 32–50% of cases, referred to as "idiopathic anaphylaxis."
It is managed in the same manner as anaphylaxis. Anaphylactoid reaction, non-immune anaphylaxis, or pseudoanaphylaxis, is a type of anaphylaxis that does not involve an allergic reaction but is due to direct mast cell degranulation. Non-immune anaphylaxis is the current term, as of 2018, used by the World Allergy Organization with some recommending that the old terminology, "anaphylactoid", no longer be used. Allergy skin testing
Allergy testing may help in determining the trigger. Skin allergy testing is available for certain foods and venoms. Blood testing for specific IgE can be useful to confirm milk, egg, peanut, tree nut and fish allergies.Skin testing is available to confirm penicillin allergies, but is not available for other medications. Non-immune forms of anaphylaxis can only be determined by history or exposure to the allergen in question, and not by skin or blood testing. Differential diagnosis
It can sometimes be difficult to distinguish anaphylaxis from asthma, syncope, and panic attacks. Asthma however typically does not entail itching or gastrointestinal symptoms, syncope presents with pallor rather than a rash, and a panic attack may have flushing but does not have hives. Other conditions that may present similarly include: scrombroidosis and anisakiasis. Post-mortem findings
In a person who died from anaphylaxis, autopsy may show an "empty heart" attributed to reduced venous return from vasodilation and redistribution of intravascular volume from the central to the peripheral compartment. Other signs are laryngeal edema, eosinophilia in lungs, heart and tissues, and evidence of myocardial hypoperfusion.