Ayres et al classified patients with brittle asthma into 2 types. The authors are from Heartlands Research Institute in Birmingham, England.
Criteria for Type 1 brittle asthma - both of the following:
(1) wide variability in the peak expiratory flow rate (PEFR), with > 40% diurnal variation for > 50% of the time over a period of at least 150 days
(2) maximal medical therapy (includes inhaled steroid dose equivalent to >= 1.5 mg beclomethasone)
Criteria for Type 2 brittle asthma - both of the following:
(1) sudden acute asthma attacks (episodic) occurring in less than 3 hours without an obvious trigger
(2) background of normal airway function or well-controlled asthma
The authors noted that some patients with clinical brittle asthma (repeated severe asthmatic attacks) may not fit either category.
Risk factors associated with Type 1 brittle asthma:
(2) psychosocial factors
(3) food intolerance
(4) relative immunoglobulin deficiency (with decreased serum levels of IgG and IgA)
(5) impaired perception of worsening airway function
(6) excessive doses of inhaled beta-agonist agents
There are no definite risk factors for Type 2 brittle asthma. A careful evaluation of the patient may show an underlying triggering event (exposure to fungal allergen, etc) that is not immediately obvious.
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