Idiopathic anaphylaxis
Idiopathic anaphylaxis is recurrent anaphylaxis with no identifiable trigger after a thorough evaluation, a diagnosis of exclusion that requires ruling out occult allergens and mimics, especially mast cell disorders. Acute attacks are treated with intramuscular epinephrine, and frequent attacks are prevented with scheduled antihistamines and, when needed, glucocorticoids or omalizumab.
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What this article covers
- Overview
Definition: idiopathic anaphylaxis is recurrent anaphylaxis for which no external trigger can be identified despite a thorough evaluation.
- Epidemiology
A minority of anaphylaxis: most anaphylaxis has an identifiable trigger; idiopathic cases remain after workup.
- Risk factors
Underlying mast cell disorder: systemic mastocytosis or mast cell activation syndrome.
- Pathophysiology
Mast cell mediator release without an identified trigger: attacks reflect mast cell and basophil degranulation with histamine and other mediators, but the initiating stimulus is not found.
- Clinical features
Recurrent typical anaphylaxis: urticaria, angioedema, flushing, bronchospasm, and hypotension.
- Differential diagnosis
Anaphylaxis with an occult trigger: alpha-gal (delayed mammalian meat), hidden food additives, or medications (Anaphylaxis), identified by directed testing rather than labeled idiopathic once a reproducible trigger is found.
- Diagnosis
Diagnose by exclusion after a systematic search for triggers and mimics: idiopathic anaphylaxis is established when recurrent episodes meet standard anaphylaxis criteria but no external trigger is…
- Management
First, treat each attack as anaphylaxis: epinephrine 0.3 to 0.5 mg IM into the anterolateral thigh, repeated every 5 to 15 minutes, with IV fluids, oxygen, and airway support.
- Complications
Fatal anaphylaxis: if epinephrine is delayed.
- Prognosis
Often improves over time: attack frequency tends to decline over months to years, and prophylaxis can frequently be tapered.
- Prevention
Reduce attack frequency with scheduled H1 (and H2) antihistamines, escalating to a glucocorticoid course or omalizumab for frequent attacks, and attempt to taper prophylaxis after 6 to 12 months without attacks.
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Related articles
- Anaphylaxis
Anaphylaxis is an acute, potentially fatal systemic hypersensitivity reaction from massive mast cell and basophil mediator release, presenting within minutes as skin, respiratory, cardiovascular, and gastrointestinal involvement after allergen exposure. It is a clinical, treat-first diagnosis, and intramuscular epinephrine is the immediate life-saving therapy.
- Urticaria
Urticaria is transient, pruritic, edematous wheals from mast cell histamine release, classified by duration into acute (under 6 weeks) and chronic (6 weeks or longer, usually spontaneous/idiopathic). Diagnosis is clinical with minimal testing, and treatment is stepwise second-generation H1 antihistamines up-titrated as needed, adding omalizumab for refractory chronic disease.