Background: A significant minority of patients with idiopathic pulmonary fibrosis (IPF) display features of autoimmunity without meeting the criteria for overt connective tissue disease. A link between IPF and other immune-mediated processes, such as hypothyroidism (HT), has not been reported. In this investigation, we aimed to determine whether HT is associated with IPF and if outcomes differ between patients with IPF with and without HT.
Methods: A retrospective case-control analysis was conducted. Of 311 patients referred to the University of Chicago Interstitial Lung Disease Center with an initial diagnosis of IPF, 196 met the inclusion criteria and were included in the final analysis. Each case was matched 1:1 by age, sex, and race to a control subject with COPD.
Results: HT was identified in 16.8% of cases and 7.1% of control subjects (OR, 2.7; 95% CI, 1.31-5.54; P = .01). Among patients with IPF, HT was associated with reduced survival time (P < .001) and was found to be an independent predictor of mortality in multivariable Cox regression analysis (hazard ratio, 2.12; 95% CI, 1.31-3.43; P = .002). A secondary analysis of two IPF clinical trial datasets supports these findings.
Conclusions: HT is common among patients with IPF, with a higher prevalence than in those with COPD and the general population. The presence of HT also predicts mortality in IPF, a finding that may improve future prognostication models. More research is needed to determine the biologic link between IPF and HT and how the presence of thyroid disease may influence disease progression.