Economic burden of interstitial lung disease in a commercially insured population with Sjögren syndrome in the United States

BACKGROUND: Patients with Sjögren syndrome (SjS) have substantial cost burden on the health care system; among these patients, those who develop interstitial lung disease (ILD) experience poorer quality of life and have a higher mortality risk. However, the economic burden of ILD has not been documented. OBJECTIVE: To estimate the direct health care costs associated with ILD among patients with SjS in a representative sample of the commercially insured population in the United States. METHODS: Individuals with a diagnosis of SjS between January 1, 2006, and September 30, 2015, with and without a diagnosis of ILD, were identified from the PharMetrics Plus for Academics database. The index date was defined as the later date of the first claim with a diagnosis of SjS or the first claim with a diagnosis of ILD for individuals with SjS and ILD (SjS-ILD), and the first claim with a diagnosis of SjS for SjS-only controls. All baseline variables were measured in the 180 days preindex period. A 5:1 propensity score matching was applied to controls for baseline demographic and geographic variables. The cost ratio and average marginal effect for total direct medical costs comparing SjS patients with and without ILD were estimated using a generalized linear model. Costs per health care resource utilization category were also reported. All costs were represented from a health plan payer perspective and inflated to 2020 US dollars. RESULTS: After applying the inclusion criteria, 815 SjS-ILD cases were identified and matched to 4,075 SjS-only controls based on the 5:1 propensity score matching procedure. The 180-day total cost of SjS-ILD cases was about 2 times higher compared with that of SjS-only controls (adjusted cost ratio = 1.95; 95% CI = 1.76-2.15). The average difference in total cost between patients with and without ILD was $8,814 (95% CI = $7,149-$10,479). Costs were mainly contributed from outpatient services other than physician office visit (such as radiological and pathological tests), inpatient services, and outpatient pharmacy cost components for both groups (39.4%, 38.8%, and 16.3% for SjS-ILD cases; 43.7%, 22.6%, and 22.9% for SjS-only controls, respectively). CONCLUSIONS: Total direct health care cost was substantially higher in patients with SjS and ILD compared with patients with SjS without ILD. Our findings provide the foundation for further economic evaluation for preventive strategies to reduce the clinical and economic burden imposed by ILD among patients with SjS.