Reliability, validity, responsiveness, and minimal important difference of the St. George's Respiratory Questionnaire...

Idiopathic pleuroparenchymal fibroelastosis (iPPFE) is a rare, progressive interstitial lung disease with a poor prognosis and limited treatment options. No validated instruments exist for assessing health status in patients with iPPFE. We aimed to evaluate the performance of the St. George's Respiratory Questionnaire (SGRQ) in this population.

We retrospectively analyzed data from 56 consecutive patients with iPPFE who were evaluated at Tosei General Hospital between January 2008 and May 2017. We examined internal consistency, test-retest reliability, construct validity, known-groups validity, responsiveness, and the minimal important difference (MID) for the SGRQ.

The SGRQ showed acceptable internal consistency (Cronbach's α: 0.75-0.92) and test-retest reliability (intraclass correlation coefficient: 0.79-0.93). Construct validity was supported by significant correlations between the SGRQ scores and clinically meaningful variables, including body mass index, flat chest index, and residual volume to total lung capacity ratio, which reflect distinctive features of iPPFE. Known-groups validity was supported by significant differences in the SGRQ total scores among groups categorized by the Gender-Age-Physiology index stage or history of pneumothorax/pneumomediastinum. Responsiveness was supported by significant correlations between changes in the SGRQ scores and changes in clinically meaningful variables over 12 months. Additionally, changes in the SGRQ total scores significantly differed between the stable and deteriorated groups classified by changes in forced vital capacity or the modified Medical Research Council dyspnea scale. The estimated MID for the SGRQ total score was 8.0 points.

These findings suggest that the SGRQ may be useful for assessing health status in patients with iPPFE.