Evaluation of Comorbidity Burden on Disease Progression and Mortality in Patients with Interstitial Pneumonia with Autoimmune Features: a Retrospective Cohort Study

Abstract Background Interstitial pneumonia with autoimmune features (IPAF) is a subset of interstitial lung disease that manifests with interstitial pneumonia and features of autoimmunity while not meeting classification criteria for a defined rheumatic disease. Comorbidity burden is an important prognostic indicator in various rheumatic and interstitial lung diseases, but few studies have commented on comorbidities in this population. This study was conducted to evaluate the association of individual comorbidities, the Charlson Comorbidity Index (CCI), and the Rheumatic Disease Comorbidity Index (RDCI) with lung disease progression and transplant/mortality outcomes in patients with IPAF. Methods In a retrospective study, we evaluated the prevalence and severity of comorbidities in an institutional cohort of patients with IPAF. Using Cox regression, we correlated the association of individual comorbidities and comorbidity burden using CCI and RDCI with time to lung disease progression (defined as relative forced vital capacity (FVC) decline of 10% or more) and with time to lung transplant/all-cause mortality. We compared the performance of CCI and RDCI, while adjusting for the Interstitial Lung Disease Gender-Age-Physiology (ILD-GAP) index. Results In a sample of 201 individuals with IPAF, a history of cerebrovascular accident (CVA) or cardiovascular disease (CVD), moderate to severe chronic kidney disease, or fracture was associated with a faster onset of lung disease progression, while a history of gastroesophageal reflux was protective. History of CVA/CVD, diabetes mellitus, and lymphoma were associated with a faster onset of lung transplant/death. Both CCI and RDCI were significantly associated with shorter time to lung disease progression (hazard ratio [HR] 1.11, 95% confidence interval [CI] 1.04–1.19 and HR 1.12 with 95%CI 1.00-1.26, respectively) and lung transplant/mortality (HR 1.18 [1.07–1.30] and 1.31 [1.10–1.57], respectively). Conclusions CCI and RDCI may be useful tools in assessing prognosis in patients with IPAF in terms of both lung disease progression and mortality. Prospective studies are needed to further evaluate the performance of CCI and RDCI and the impact of optimizing comorbid conditions that may mitigate poor outcomes among patients with IPAF.