Comparison of three groups of patients with usual interstitial pneumonia

Objective: To determine the clinical characteristics and outcomes of patients with lungdominant connective tissue disease (LD-CTD) with a usual interstitial pneumonia (UIP) who do not meet the criteria for any form of CTD, and to compare these parameters with those of patients with idiopathic pulmonary fibrosis (IPF/UIP) and CTD-associated-UIP.

Methods: We conducted a prospective study on 118 patients diagnosed with UIP [LD-CTD, n = 28; CTDUIP, n = 29; and IPF/UIP, n = 61]. We compared the clinical characteristics, physiological findings, serum albumin concentrations, high-resolution computed tomography (HRCT) imaging data, and outcomes among the three groups and used Cox's proportional hazards regression analysis to identify variables associated with an increased risk of death.

Results: The LD-CTD and CTD-UIP patients were younger, more often female, and predominantly nonsmokers, compared with the IPF/UIP group. A significant difference in survival was evident between patients in the CTD-UIP and IPF/UIP groups (p = 0.028), but not between LD-CTD and IPF/UIP (p = 0.164) or between LD-CTD and CTD-UIP (p = 0.254). The variables associated with poorer survival in all UIP patients were (reduced) initial SpO2 level (hazard ratio [HR], 2.89; 95% confidence interval [CI] 2.1-3.7; p = 0.009) and lower serum albumin concentration (HR 2.16; 95% CI 1.6-2.7; p = 0.008).

Conclusions: LD-CTD has distinct clinical characteristics that suggest an autoimmune background resembling that of CTD-UIP but differing from that of IPF/UIP. However, LD-CTD with a UIP pattern was not associated with improved survival. The resting oxygen saturation level and serum albumin concentration were independent predictors of mortality in all of the studied UIP patients, regardless of UIP type.