Correlation of the degree of dyspnea with health-related quality of life, functional abilities, and diffusing capacity for carbon monoxide in patients with systemic sclerosis and active alveolitis: results from the Scleroderma Lung Study

Abstract

Objective: To determine whether baseline self-assessment measures of health status and physiologic indices of disease severity in alveolitis-positive patients with systemic sclerosis (SSc) correlate with the severity of their dyspnea, and to quantify functional impairment in patients with scleroderma lung disease and compare it with that in patients with chronic obstructive pulmonary disease (COPD).

Methods: SSc patients (n = 138) with diffuse (n = 81) or limited (n = 57) cutaneous disease and active alveolitis (determined by bronchoalveolar lavage and/or high-resolution computed tomography) who participated in the National Heart, Lung, and Blood Institute-sponsored, multicenter, parallel-group, double-blind, randomized, placebo-controlled trial of oral cyclophosphamide for treatment of SSc-associated interstitial lung disease were evaluated. Pearson's univariate correlations were determined between the Short Form 36 (SF-36) physical component summary (PCS) and mental component summary (MCS) scales, functional questionnaires, and physiologic parameters of breathing (forced vital capacity [FVC] and single-breath diffusing capacity for carbon monoxide [DLCO]). Student's t-test was used to compare subgroups. Scores from 2 instruments for self-assessment of breathlessness, Mahler's baseline dyspnea index (BDI) and a visual analog scale (VAS) for breathing, were divided at the median. Values for the DLCO and FVC (% predicted) were divided based on the American Thoracic Society guidelines for mild (>70% of predicted), moderate (50-70% of predicted), and severe (<50% of predicted) physiologic impairment.

Results: Scores on the BDI and VAS for breathing were highly correlated (r = -0.61). The PCS and MCS were able to differentiate patients with more breathlessness (measured by BDI and VAS for breathing) and more abnormal physiologic measures (FVC and DLCO). In SSc patients with alveolitis, all 8 domains of the SF-36 were significantly impaired as compared with the healthy population and were similar to those reported by patients with COPD.

Conclusion: The SF-36 was able to discriminate between scleroderma lung disease patients with more severe and less severe breathlessness, the primary symptom of active alveolitis. The SF-36 complements the BDI and VAS scores for breathing in scleroderma lung disease and is variably correlated with results of pulmonary function tests, suggesting that the SF-36 should be included as an outcome measure in intervention trials in this population.