For patients with idiopathic pulmonary fibrosis (IPF), disease-specific measures can be as important as their length of survival. However, quality of life (QOL) for these patients remains largely undefined and few studies have assessed the usefulness of generic QOL instruments for estimating disease-specific measures (using QOL and functional impairment instruments) in patients with IPF.
The Sildenafil Trial of Exercise Performance in IPF (STEP-IPF) enrolled 181 patients with confirmed IPF diagnosis and <35% predicted diffusing lung capacity. At baseline, we used linear regression models to estimate St. George's Respiratory Questionnaire Total Score (SGRQ-Total) and its three component scores (SGRQ-Activity, SGRQ-Impact and SGRQ-Symptom). We also estimated three measures of functional impairment: actual forced vital capacity (FVC), walk distance and a pre-walk modified Borg dyspnea scale rating (Borg dyspnea). Predictors for the four SGRQ scores included patient age, sex and data from three generic QOL instruments: the EuroQOL 5-D summary score (EQ-5D), the ICECAP index of capability for older people summary index (ICECAP), and component scores from the Medical Outcomes Study Short Form 36 (SF-36). For the three functional impairment measures we also included the University of California at San Diego Shortness of Breath Questionnaire (SOBQ) and the SGRQ components as predictors.
Overall, generic QOL instruments explain a greater amount of variance for the SGRQ-Total (R2 = .67), SGRQ-Activity (R2 = .66), and SGRQ-Impact (R2 = .58) than for the SGRQ-Symptoms (R2 = .28), FVC (R2 = .28), walking distance (R2 = .16), and Borg dyspnea (R2 = .15). The most important predictors across all disease-specific measures include the SF-36 physical and social function scores and the ICECAP summary index. Typically, sex and age were not significant predictors.
For patients with IPF, generic QOL instruments are better predictors of disease-specific QOL measures than they are of functional-impairment measures.
Generic QOL instruments are useful adjuncts to disease-specific measures. However, they are not sufficient to replace disease-specific QOL and functional-impairment measures for IPF patients.
Eric Eisenstein, No Financial Disclosure Information; No Product/Research Disclosure Information