Minimal Clinically Important Difference for Worsening of the University of California San Diego Shortness of Breath Questionnaire in Patients With Idiopathic Pulmonary Fibrosis With Mild or Moderate Impairment in Lung Function

Background

The University of California San Diego Shortness of Breath Questionnaire (UCSD-SOBQ) is used commonly in clinical trials to evaluate dyspnea in patients with idiopathic pulmonary fibrosis (IPF). Previously, the minimal clinically important difference (MCID) for UCSD-SOBQ was estimated at 8 points for patients with IPF with severe impairment as determined by lung function tests.

Research Question

What is the MCID threshold for UCSD-SOBQ worsening in patients with IPF and less physiologic impairment?

Study Design and Methods

Pooled data from patients with baseline forced vital capacity (FVC) of ≥ 50% predicted enrolled in the 2 randomized phase 3 CAPACITY trials of pirfenidone (ClinicalTrials.gov Identifiers: NCT00287716 and NCT00287729) were analyzed. Over the 72-week treatment period, the MCIDs for the UCSD-SOBQ were estimated using anchor-based methods by comparing changes in UCSD-SOBQ scores with values for stability/improvement vs worsening in 4 candidate anchors: FVC, diffusing capacity of the lungs for carbon monoxide (Dlco), 6-minute walk distance (6MWD), and St George’s Respiratory Questionnaire activity domain (SGRQ-A). Anchors that correlated with UCSD-SOBQ scores for at least 1 measurement (correlation coefficient ≥ 0.3) were included for MCID determination in a receiver operating characteristics approach.

Results

Overall, UCSD-SOBQ score changes were similar within stability/improvement and worsening categories for FVC, Dlco, and 6MWD anchors. For the SGRQ-A anchor, for stability/improvement, UCSD-SOBQ changes were lower than for the other anchors; for worsening, changes were greater. Based on suitable correlation coefficients, FVC, 6MWD, and SGRQ-A were the anchors used to triangulate the MCID. Optimal anchor cut points (MCID) for worsening were 6 for FVC, 4.3 for 6MWD, and 5.8 for SGRQ-A, which resulted in a z-transformed weighted average for UCSD-SOBQ worsening of 5.97.

Interpretation

Our results show that in patients with IPF and mild or moderate physiologic impairment, the UCSD-SOBQ has a MCID for worsening of 4 to 6 with a point estimate of 6.

Trial Registry

ClinicalTrials.gov; No.: NCT00287716 and NCT00287729; URL: www.clinicaltrials.gov