Contribution of Peripheral Airways Dysfunction to Poor Quality of Life in Sarcoidosis

Abstract

Background: Sarcoidosis is characterized by reduced quality of life (QoL), yet QoL is correlated poorly to conventional spirometric lung function tests.

Research question: What is the relationship of a QoL measure with comprehensive lung function assessment using oscillometry in sarcoidosis?

Study design and methods: Sixty-two patients with pulmonary sarcoidosis completed the St. George's 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 results were determined with Spearman rank coefficient (ρ), and receiver operating characteristic curves were 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 score (resistance at 5 Hz [R5], ρ = 0.43 [P < .01]; R5 minus resistance at 20 Hz [R20], ρ = 0.35 [P < .01]; reactance at 5 Hz [X5], ρ = -0.42 [P < .01]; reactance area under the curve [Ax], ρ = 0.44 [P < .01]), whereas FVC % predicted and residual volume to total lung capacity ratio, were related weakly to SGRQ score (ρ = -0.30 [P = .02] and ρ = 0.30 [P = .02], respectively). Oscillometry reactance, measuring elastic properties of the lung, predicted an impaired QoL (area under the receiver operating characteristic curve: Ax, 0.80 [P < .001] and X5, 0.78 [P < .001]), even in patients with absence of an obstructive or restrictive spirometry pattern. Ax remained associated significantly with SGRQ score even after adjustment for FVC and Scadding stage on multivariable analysis (P = .005). Feno was not associated with SGRQ score. Peripheral airway function parameters (R5 minus R20, Ax, and residual volume to total lung capacity ratio) were grouped in an independent cluster, whereas X5 constituted a single cluster.

Interpretation: Our results indicate that oscillometric lung function parameters, especially those of peripheral airway dysfunction, are correlated more strongly to a QoL measure than spirometry in patients with sarcoidosis.

Keywords: exhaled nitric oxide; lung function; oscillometry; peripheral airways; quality of life; sarcoidosis.