Size of Inhaled Corticosteroid and Small Airway Inflammation in Asthma

99 On the basis of knowledge that asthma is a chronic inflamma-tory disorder of the airways, evidence-based practice guidelines have recommended anti-inflammatory controller therapy to improve asthma outcomes during the past 3 decades. Recently published guidelines have emphasized the role of anti-inflammatory maintenance therapy to prevent chronic persistence and troublesome exacerbations of asthma by controlling asthma risk factors. 1-3 Regular use of inhaled corticosteroids (ICS) can reduce asthma exacerbation rates, 4 decrease bronchial hyperresponsiveness. 5 and prevent loss of lung function. 6 In addition, a large retrospective case-control study demonstrated a reduced rate of asthma mortality by regular use of ICS. 7 Several decades ago, the importance of small airway dysfunc-tion was clearly identified in asthmatics. There are 3 main lung regions: the large (>2 mm) conducting airway zone, the small (<2 mm) conducting airway zone, and the respiratory acinar zone. 8 Inflammation in asthma definitely involves large airways , but histopathological evidence has clearly shown that the inflammation involves small airways as well. 9 Small airway dys-function may be more implicated in unstable asthma. 10 Asthmatic patients who continue to experience poor disease control and frequent exacerbations exhibit persistent airways inflammation that is not well controlled by existing anti-inflammatory drugs. More specifically, a key contributory factor for poor disease control may be ongoing and unopposed inflammation as well as dysfunction of small airways. 11 Smokers and patients with unstable asthma may have more prominent small airway disease. Therefore, clinicians should not underestimate the presence of small airway dysfunction. Inhaler devices that have been routinely used in clinical practice may not effectively deliver ICS into small airways. With advances in inhaler technologies for delivering drug to the whole respiratory tree, greater consideration has been focused on the treatment of the small airway region. In particular, the role of fine and ultrafine particles has been explored in the management of patients with asthma. ICS is available in pressurized metered dose inhalers (pMDI) using a hydrofluoroalkane (HFA) propellant for both fine-particle formulations with a particle mass median aerodynamic diameter (MMAD) of 2-4 μm and aerosols of extrafine particles with an MMAD of 1 μm. 12 Recently , patients with poor inhaler techniques have benefited from extrafine-particle ICS. 13 In this issue, Postma et al. 14 compared asthma-related outcomes after patients initiated extrafine-particle ciclesonide or fine-particle ICS (fluticasone propionate or non-extrafine be-clomethasone) in a matched cohort study that prescribed the first ICS as …