What is ‘aspirin-induced asthma’?
Aspirin-induced asthma (AIA) is a distinct clinical entity and appears to be
a specific subtype of asthma. It is characterised by asthma triggered within one
to three hours of ingestion of aspirin and other non-steroidal anti-inflammatory
drugs (NSAIDs). The asthma attack is often accompanied by or even preceded by
symptoms of rhinitis (nasal obstruction, rhinorrhoea and sneezing) and facial
flushing. The asthma attack triggered by aspirin and NSAIDs may be very severe
and life threatening. The common feature of medications that trigger this
reaction is their inhibition of the cyclo-oxygenase 1 (COX-1) enzyme.2
<LE IV>
The clinical picture of this asthma syndrome differs from that of the
majority of patients with childhood onset or allergic asthma. The initial onset
of symptoms appears at an average age of 30 years, with rhinitis characterised
by persistent watery rhinorrhoea, nasal obstruction and sneezing. Loss of a
sense of smell, with development of troublesome nasal polyps (often requiring
repeated nasal polypectomies), occurs in up to two thirds of patients. On
average, asthma develops two years after the onset of rhinitis, with intolerance
to aspirin and other NSAIDs occurring about four years later.3
<LE III-3> Other names for this syndrome include Francis’ Triad,
Samter’s Triad and the Aspirin Triad.4
As previously mentioned, it may co-exist with other patterns and subtypes of
asthma.
Patients with AIA may often be unaware of their intolerance to aspirin. They
may have taken aspirin or NSAIDS in the past, before onset of this syndrome,
without any adverse reactions. However, in contrast to other types of allergies,
the development of AIA does not depend on having had previous exposure to
aspirin or NSAIDs. Although avoidance of all NSAIDS is important to prevent
acute attacks, the condition tends to be progressive, despite avoidance of these
medications. Avoidance of dietary salicylates has not been shown to improve the
condition.
Other Terms for Aspirin-Induced Asthma (AIA)
- Aspirin-sensitive asthma
- Aspirin-intolerant asthma
- NSAID-induced rhinitis and asthma
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How common is aspirin-induced asthma?
Reports of the prevalence of this condition in adults with asthma have varied
between 3-22%,5 <LE I>
depending on the diagnostic methods used. Recent Australian data based on
questionnaires alone show that about 10-11% of adults with asthma report asthma
triggered by aspirin or NSAIDs.6
<LEIII-2> However, prevalence by oral
provocation testing was estimated at 22% in adults, 10% in children, according
to a recent evidence-based review. 5
<LE I> The condition appears to be more common in
patients with moderate to severe persistent asthma, particularly those with a
history of nasal polyposis. Many of these patients are not atopic, and have
increased baseline production of leukotrienes.
What is the mechanism of aspirin-induced asthma?
The central characteristic of these patients is their
sensitivity to medications that inhibit the COX-1 enzyme. The COX enzymes
produce a range of mediators that are responsible for regulating normal body
functions (mainly COX-1) as well as inflammation, fever and pain (mainly COX-2).
One of the mediators produced by COX-1 that regulates normal body function is
prostaglandin E2. Evidence suggests that reduction of prostaglandin E2 levels by
medications that inhibit COX allows activation of an enzyme pathway to produce
increased amounts of inflammatory mediators called leukotrienes.
These leukotrienes are responsible for many of the manifestations of an asthma
attack, triggered in these patients by aspirin and NSAIDs.
Figure 1 The mechanism of aspirin-induced asthma
