Idiopathic anaphylaxis: What causes it?

I recently had my third anaphylactic reaction, and my doctors still haven't identified a cause. All my allergy tests are negative. But my doctor wants me to carry an epi pen in case it happens again. I am freaking out about it. What else can be done to identify the cause of my anaphylaxis?

- Alexandra / New Jersey

Answer

I understand your concern. The term "anaphylaxis" is generally used to describe a serious and life-threatening allergic reaction. During an anaphylactic reaction, various tissues in your body release histamine and other substances. This results in itching, hives, dizziness, wheezing or shortness of breath — all of which can be very frightening.

However, it's possible to have anaphylaxis signs and symptoms that aren't triggered by an allergic reaction. In such cases, the cause isn't clear. But in some people, it may be due to an overabundance of histamine-containing cells (mast cells). When the cause of anaphylaxis can't be determined, doctors refer to it as idiopathic anaphylaxis.

The medical evaluation of anaphylaxis is complicated. The first step often is to establish that the problem is anaphylaxis and not another medical condition, such as hereditary angioedema or systemic mastocytosis. This includes a thorough history and physical examination. The next step is testing for allergy and related medical conditions. If no allergen or medical condition can be identified as a cause, a diagnosis of idiopathic anaphylaxis may be considered.

If you're diagnosed with idiopathic anaphylaxis, it is important to wear a medical alert bracelet or necklace. It's also important for you and your doctor to develop an emergency plan that specifies what you should do in the event of an anaphylactic attack. Many doctors recommend self-administered epinephrine for people with idiopathic anaphylaxis. Your doctor may also recommend prednisone or antihistamines to reduce the risk of another attack.

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