BACKGROUNDEvidence has demonstrated that the distal lung, which includes airways of < 2 mm in diameter and lung parenchyma, constitutes an important component of asthma pathology. Cysteinyl leukotrienes (CysLTs) are potent proinflammatory mediators and bronchoconstrictors involved in the asthmatic process. Guidelines recommend the leukotriene-modifying agents for asthma treatment. We hypothesized that a leukotriene receptor antagonist with an inhaled corticosteroid (ICS) and long-acting β2 agonist (LABA) combination would improve small airways function in moderate-to- severe asthmatics evaluated by physiological tests and high-resolution computed tomography (HRCT) analysis. This study was performed at a tertiary university hospital in Beijing.

METHODSThis was a randomized, double-blind, parallel study performed in 38 patients with moderate-to-severe asthma treated with salmeterol/futicasone (SFC) plus montelukast (SFC+M) or SFC plus placebo over 24 weeks. Small airway function was assessed by physiological studies and HRCT image analysis.

RESULTSMontelukast significantly improved air trapping as expressed by the residual volume (RV)/total lung capacity (TLC). Over 24 weeks of treatment, RV/TLC was improved by (15.41 ± 6.67)% in patients receiving SFC+M while RV/TLC was decreased by (8.57 ± 10.26)% in patients receiving SFC alone, the difference between the two groups was significant (P = 0.02). There was a trend towards a significant difference in forced expiratory volume in the first second (FEV1)/forced vital capacity (FVC) in the SFC+M group compared to that in the SFC group ((17.87 ± 8.17)% vs. (12.28 ± 9.20)%, P = 0.056). There was no significant change in percentage wall area (WA%) after 24 weeks of add-on treatment with montelukast. Patients receiving SFC+M showed significant improvement in the ratio of CT-determined values at full expiration to those at full inspiration (E/I ratio) (0.894 ± 0.005 vs. 0.871 ± 0.003, P = 0.002).

CONCLUSIONWe have shown, using lung function tests and HRCT image technique, that add-on therapy with montelukast improves distal lung function reflected by air trapping, but not airway wall thickness in moderate-to-severe asthma.