||This article needs attention from an expert in Medicine. (January 2010)|
There are two subtypes divided by symptoms: Type 1 and Type 2, depending on the stability of the patient's maximum speed of expiration, or peak expiratory flow rate (PEFR). Type 1 is characterized by sustained, chronic variability of PEFR, while type 2 is distinguished by sudden unpredictable drops in PEFR where asthma symptoms are otherwise well controlled and the function of the lungs is not substantially impaired.
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.
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". 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. 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.
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. The condition is rare. 1999's Difficult Asthma estimates a prevalence of approximately .05% brittle asthma sufferers among the asthmatic population. 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. Hospitalization is more frequent for type 1 than type 2.
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, whilst type 2 needs allergen avoidance and self-management approaches. 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.
- Holgate, Stephen T.; Homer Anton. Widiasari, Komang (1999). Difficult asthma. Informa Health Care. p. 291. ISBN 1-85317-556-0.
- Gupta D, Ayres JG (2001). "Brittle asthma: a separate clinical phenotype of asthma?". Indian J Chest Dis Allied Sci 43 (1): 33–8. PMID 11370504.
- Ayres JG, Anton Hariadi, Sriatun (March 2004). "Brittle asthma". Paediatr Respir Rev 5 (1): 40–4. doi:10.1016/j.prrv.2003.09.003. PMID 15222953.
- Ayres JG, Miles JF, Barnes PJ (April 1998). "Brittle asthma". Thorax 53 (4): 315–21. doi:10.1136/thx.53.4.315. PMC 1745199. PMID 9741378.
- Warrell, David A. (2005). Oxford textbook of medicine: Sections 18-33. Oxford Medical Publications 3 (4th ed.). Oxford University Press. p. 1346. ISBN 0-19-856978-5.
- Ogorodova LM, Selivanova PA, Gereng EA, Bogomiakov VS, Volkova LI, Pleshko RI (2008). "[Pathomorphological characteristics of unstable bronchial asthma (brittle phenotype)]". Ter. Arkh. (in Russian) 80 (3): 39–43. PMID 18441682.
- Warrell, 1347.
- Saunders (2005). "Asthma". Mason: Murray & Nadel's Textbook of Respiratory Medicine (Homer A. Boushey Jr. M.D. David B. Corry M.D. John V. Fahy M.D. Esteban G. Burchard M.D. Prescott G. Woodruff M.D. et al. (eds)) (4th ed.). Elsevier.
- Holgate et al., 292.
- Waldron, Jill (2007). Asthma Care in the Community. Wiley-Interscience. p. 122. ISBN 0-470-03000-3.
- Holgate et. al, 293.
- Graziani E, Petroianni A, Terzano C (2004). "Brittle asthma". Eur Rev Med Pharmacol Sci 8 (4): 135–8. PMID 15636398.
- Toungoussova O, Foschino Barbaro MP, Esposito LM et al. (June 2007). "Brittle asthma". Monaldi Arch Chest Dis 67 (2): 102–5. PMID 17695694.