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:
(1) atopy
(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.
