Patients with possible usual interstitial pneumonia (UIP) constitute a substantial group, and their clinical characteristics and outcomes are not well defined. We compared the clinical characteristics and survival between patients with possible UIP and the UIP pattern.

We evaluated 62 patients with possible UIP and 544 patients with the UIP pattern. Both groups were diagnosed by clinical characteristics and high-resolution computed tomography (HRCT) findings. Two radiologists performed radiological evaluation based on the new idiopathic pulmonary fibrosis (IPF) guidelines. Two risk-stratification methods were used to compare UIP pattern and possible UIP patients.

The groups had similar demographic and clinical characteristics. Pulmonary function tests revealed no significant differences in lung volumes between the 2 groups. However, DLCO was significantly lower with the UIP pattern than with possible UIP (p = 0.004). Multivariate analysis showed age, sex, and carbon monoxide diffusing capacity (DLCO) as important independent variables for survival. The UIP HRCT pattern did not affect survival (hazard ratio, 0.83; 95% confidence interval, 0.51–1.24; p = 0.32). Possible UIP was not associated with prognosis when independent predictors for survival rate and propensity score were considered. In the case-control study, the 3-year survival rate was 44.6% in the UIP pattern group and 56.8% in the possible UIP group (p = 0.16).

Clinical characteristics and outcomes were similar in possible UIP and UIP patients, except for differences in DLCO. The UIP pattern itself did not affect survival.