Pseudoallergy

Key takeaways

Pseudoallergy belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Pseudoallergy to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Pseudoallergy from memory before moving on to harder problems.

Reference excerpt

Pseudoallergy, sometimes known as nonallergic hypersensitivity, is a type of hypersensitivity reaction mostly described in the context of drug allergy. The mechanism is somewhat similar to the type 1 hypersensitivity in the Gell and Coombs classification in that the effector cell is also mast cell. In pseudoallergic reaction, the mast cell is directly activated, rather than through the mediation of Immunoglobulin E (IgE). Therefore, it is also known as direct mast cell activation. Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs), along with certain food ingredients and additives like tartrazine, benzoates, and salicylates, are the most common causes of pseudoallergic reactions. Since these reactions don't require IgE sensitization, they may manifest themselves after only one exposure. Doses-dependent, pseudoallergic reactions typically involve substances that are chemically unrelated to each other. The lack of information in skin tests and serology makes the diagnosis challenging. Nonallergic hypersensitivity is diagnosed on the basis of symptoms. Oral challenge tests can be used to confirm pseudoallergy in the proper clinical context, i.e. a person consumes progressively larger quantities of a suspected allergen under medical supervision.

Signs and symptoms Clinically, pseudoallergy and anaphylaxis are identical. Pseudoallergy symptoms include gastrointestinal symptoms, urticaria, bronchospasm, and angioedema, along with headache, edema, skin flushing, hypotension, and shock.

Causes Although they are commonly used to treat pain related to fractures, opioid medications have well-known side effects. Almost all opioids have the ability to directly induce mast cell degranulation, which in turn can result in pseudoallergy. Opioid medications, including morphine, codeine, and meperidine, have been known to cause pseudoallergy. By directly activating mast cells, opioids cause histamine release, which results in flushing or pruritus that is almost always mistaken for allergy symptoms. Compared to other opioids, codeine and morphine have been shown to be more likely to cause mast cell degranulation. By using a non-immunologic mechanism that is not dependent on IgE or the high-affinity IgE receptor FcεRI, codeine causes pseudoallergy. This suggests that codeine may activate mast cell degranulation by acting on the opioid receptor.

Mechanism One recognized mechanism is through the activation of mast cell receptor Mas-Related G Protein-Coupled Receptor-X2 (MRGPRX2). MRGPRX2 is a G protein-coupled receptor capable of recognizing both endogenous and exogenous stimuli, therefore activating the degranulation of mast cell, results in pseudoallergic reaction. MRGPRX2 is expressed in mast cells (particularly connective tissue mast cells [MCTC] found in the skin), sensory neurons, and keratinocytes. Comparing to type 1 hypersensitivity, MRGPRX2-mediated response is more rapid and transient. It is proposed that single nucleotide polymorphism of this receptor may results in different reaction among individuals, although clinical significance is undertermined. Other mechanisms results in direct mast cell activation are suggested, including complement receptors (CR3, CR4, CR3a, CR5a) activated by the respective complement factors; toll-like receptors activated by bacterial lipopolysaccharide or peptidoglycan; surface IgE receptors (FcεRI, FcεRII) activated by autoantibodies or parasites; IgG receptors (FcγRII) activated by pathogen-specific IgG; Cysteinyl leukotriene receptors (CysLT1R/2R) activated by cysteinyl leukotrienes; Protease-activated receptors (PAR2) activated by other mast-cell proteases. While pseudoallergy and IgE-mediated allergy share some similarities in their clinical manifestations, pseudoallergy is not the same as common allergy or type 1 reactions. Pseudoallergy can be caused by a variety of medications through various pathways. For example, taxol can cause pseudoallergy by stimulating the complement system. The reaction occurs for the first time without any prior sensitization.

See also Anaphylaxis Type I hypersensitivity

References

Further reading Zuberbier, T (1999). "Pseudoallergy or nonallergic hypersensitivity". Allergy. 54 (4): 397–400. doi:10.1034/j.1398-9995.1999.00155.x. ISSN 0105-4538. PMID 10371101. S2CID 29977457. Waller, Derek G. (April 11, 2011). "Allergy, pseudo-allergy and non-allergy". British Journal of Clinical Pharmacology. 71 (5). Wiley: 637–638. doi:10.1111/j.1365-2125.2011.03976.x. ISSN 0306-5251. PMC 3093068. PMID 21480945.

External links The Free Dictionary UpToDate - NSAIDs (including aspirin): Allergic and pseudoallergic reactions

Worked examples

Example 1 — a first encounter with Pseudoallergy

Start with the simplest possible case. Write down what Pseudoallergy claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Pseudoallergy before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Pseudoallergy ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Pseudoallergy

In research: Pseudoallergy appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Pseudoallergy in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Pseudoallergy is common in secondary-school and first-year university syllabi. It links to neighbouring topics Allergology, so understanding it makes those chapters shorter.
In everyday life: Look for Pseudoallergy outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Pseudoallergy in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Pseudoallergy means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Pseudoallergy out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Pseudoallergy in simple terms?

Pseudoallergy, sometimes known as nonallergic hypersensitivity, is a type of hypersensitivity reaction mostly described in the context of drug allergy. The mechanism is somewhat similar to the type 1 hypersensitivity in the Gell and Coombs classification in that the effector cell is also mast cell.

Why does Pseudoallergy matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Pseudoallergy?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Pseudoallergy.