A 15-year-old boy is subjected to recurrent attacks of asthma. A careful clinical history reveals that the asthma attacks occur most frequently after aspirin administration. Which of the following is the pathogenetic mechanism in this form of asthma?
First, I remember that there's a condition called aspirin-exacerbated respiratory disease (AERD), which is also known as Samter's triad. It includes asthma, nasal polyps, and aspirin sensitivity. The key here is the aspirin-induced asthma attacks.
The core concept here is the mechanism by which NSAIDs like aspirin trigger asthma. Normally, prostaglandins are synthesized via the COX enzymes. When COX is inhibited by aspirin, there's a shunting of arachidonic acid metabolism towards the lipoxygenase pathway, leading to increased leukotrienes. Leukotrienes are potent bronchoconstrictors and can cause inflammation in the airways. This is different from typical allergic asthma, which involves IgE mechanisms.
The correct answer should relate to the COX pathway inhibition leading to increased leukotrienes. Let's check the options. The options aren't listed here, but the correct answer is likely about the shunting of arachidonic acid metabolism from COX to lipoxygenase pathways, causing excess leukotriene production.
The wrong options might include things like IgE-mediated reactions, mast cell degranulation without COX involvement, or activation of H1 receptors. Each of these doesn't fit the mechanism here. For example, IgE is involved in allergic asthma, not aspirin-induced. Mast cell degranulation could be a red herring if the actual issue is the metabolic pathway shift. H1 receptors are more related to antihistamines, which isn't the case here.
Clinical pearl: Remember that AERD is associated with increased leukotriene production due to COX inhibition. Patients with this condition often have nasal polyps and chronic rhinosinusitis. Avoiding NSAIDs is crucial, and leukotriene receptor antagonists like montelukast are helpful.
So the correct answer is the option that states the shunting of arachidonic acid metabolism from COX to lipoxygenase pathways, leading to increased leukotrienes.
**Core Concept**
This question explores the pathophysiology of **aspirin-exacerbated respiratory disease (AERD)**, a form of non-IgE-mediated asthma triggered by cyclooxygenase (COX) inhibition. The key mechanism involves **shunting of arachidonic acid metabolism** from the COX pathway to the 5-lipoxygenase (5-LOX) pathway, leading to **excessive leukotriene production**.
**Why the Correct Answer is Right**
Aspirin inhibits COX-1 and COX-2 enzymes, which normally synthesize prostaglandins and thromboxanes. In AERD patients, this inhibition causes **diversion of arachidonic acid** into the 5-LOX pathway. This results in **overproduction of cysteinyl leukotrienes** (e.g., LTC4, LTD4), which are potent **bronchoconstrictors** and **mucosal edema inducers**. Leukotrienes also enhance vascular permeability and mucus secretion, exacerbating asthma and nasal polyps.
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