Peripheral airways dysfunction is a major contributor to poor quality of life in sarcoidosis

Sarcoidosis is characterized by reduced quality of life (QoL), yet QoL is poorly correlated to conventional spirometric lung function tests. What is the relationship of a QoL measure with comprehensive lung function assessment using oscillometry in sarcoidosis?. Sixty-two patients with pulmonary sarcoidosis completed the St George Respiratory Questionnaire (SGRQ), a respiratory QoL measure, and underwent lung function assessment including oscillometry, spirometry, diffusion capacity, fractional exhaled nitric oxide (FENO) and body plethysmography. Relationships of lung function parameters with SGRQ were determined with Spearman's rank coefficient (rho), and receiver-operating characteristic curves plotted. Logistic regression and hierarchy cluster analysis of parameters from multiple lung function techniques were performed RESULTS: Oscillometric indices describing peripheral lung dysfunction, showed significant associations with SGRQ (R5, rho=0.43, p<0.01, R5-R20, rho=0.35, p<0.01, X5, rho=-0.42, p<0.01, Ax, rho=0.44 <0.01), whereas FVC% and RV/TLC ratio, were weakly related to SGRQ (rho=-0.30, p=0.02, rho=0.30, p=0.02). Oscillometry reactance, measuring elastic properties of the lung, predicted an impaired QoL (AUC, Ax, 0.80, p<0.001 and X5, 0.78, p<0.001), even in patients with absence of an obstructive or restrictive spirometry pattern. Ax remained significantly associated with SGRQ even after adjustment for FVC and Scadding stage on multivariable analysis (p=0.005). FENO was not associated with SGRQ. Peripheral airway function parameters (R5-R20, Ax, RV/TLC) were grouped in an independent cluster, whereas X5 constituted a single cluster INTERPRETATION: Oscillometric lung function parameters, especially those of peripheral airway dysfunction, are more strongly correlated to a QoL measure than spirometry in patients with sarcoidosis.