| Prevention: | Allergen avoidance and self-management approach |
Brittle asthma is a type of asthma distinguishable from other forms by recurrent, severe attacks.[1] [2] [3] There are two subtypes divided by symptoms: Type 1 and Type 2,[4] depending on the stability of the patient's maximum speed of expiration, or peak expiratory flow rate (PEFR). Type 1 is characterized by a maintained wide PEF variability despite considerable medical therapy including a dose of inhaled steroids, and Type 2 is characterized by sudden acute attacks occurring in less than three hours without an obvious trigger on a background of well controlled asthma.[5]
Brittle asthma is one of the "unstable" subtypes of "difficult asthma", a term used to characterize the less than 5% of asthma cases that do not respond to maximal inhaled treatment, including high doses of corticosteroids combined with additional therapies such as long-acting beta-2 agonists.[6] [7]
The 2005 Oxford Textbook of Medicine distinguishes type 1 brittle asthma by "persistent daily chaotic variability in peak flow (usually greater than 40 per cent diurnal variation in PEFR more than 50 per cent of the time)", while type 2 is identified by "sporadic sudden falls in PEFR against a background of usually well-controlled asthma with normal or near normal lung function".[8] In both types, patients are subject to recurrent, severe attacks. The cardinal symptoms of an asthma attack are shortness of breath (dyspnea), wheezing, and chest tightness.[9] Individuals with type 1 suffer chronic attacks in spite of ongoing medical therapy, while those with type 2 experience sudden, acute and even potentially life-threatening attacks even though otherwise their asthma seems well managed.[10]
When first defined by Margaret Turner-Warwick in 1977, the term brittle asthma was used specifically to describe type 1, but as studies into the phenotype were conducted the second type was also distinguished.[11]
In addition to any issues of treatment compliance, and maximised corticosteroids (inhaled or oral) and beta agonist, brittle asthma treatment also involves for type 1 additional subcutaneous injections of beta2 agonist and inhalation of long acting beta-adrenoceptor agonist,[12] whilst type 2 needs allergen avoidance and self-management approaches.[13] Since catastrophic attacks are unpredictable in type 2, patients may display identification of the issue, such as a MedicAlert bracelet, and carry an epinephrine autoinjector.[8]
The condition is rare. 1999's Difficult Asthma estimates a prevalence of approximately 0.05% brittle asthma sufferers among the asthmatic population.[14] Though found in all ages, it is most commonly found in individuals between the ages of 18 and 55; it is present in both sexes, though type 1 has been diagnosed in three times as many women as men.[14] Hospitalization is more frequent for type 1 than type 2.[14]