Interstitial lung disease (ILD) is becoming more prevalent in patients with RA while shortening survival and leading to substantial health care costs, according to a retrospective study of RA-ILD prevalence, incidence, costs, and mortality.
“To our knowledge, this is the first study to describe the incidence and prevalence of RA-ILD among the general population and to estimate costs among U.S. patients with RA-ILD,” wrote lead author Karina Raimundo, principal health economist at Genentech, and her coauthors in the Journal of Rheumatology.
The study reviewed data from the Truven Health MarketScan Commercial and Medicare Supplemental health insurance databases, along with linking a subset of patients to the Social Security Administration Death Index to determine mortality. From 2004 to 2013, with the number of patients ranging from 892 to 3,232 per year, yearly prevalence estimates ranged from 3.2 (95% confidence interval, 3.0-3.4) to 6.0 (95% CI, 5.7-6.2) RA-ILD cases per 100,000 people. Yearly incidence ranged from 2.7 (95% CI, 2.5-2.9) to 3.8 (95% CI, 3.5-4.0) cases per 100,000 people.
While incidence was relatively stable, prevalence increased over the 10-year period. The authors noted that increased prevalence suggests improved survival of RA-ILD patients but were unable to definitively state why, with explanations ranging from more effective therapies to earlier diagnosis of the disease. “Our data do not allow more in-depth evaluation of this issue, and it merits further analysis.”
In addition, they found that average yearly costs across all study years ranged from $40,941 (standard deviation, $55,682) to $51,849 (SD, $77,125), with the main cost drivers being inpatient admissions, outpatient services, and outpatient pharmacy. By the 5-year mark of first diagnosis, 35.9% of RA-ILD patients who could be linked to the SSDI had died; those patients – with a mean age of 65 years – also had a median survival of 7.8 years (95% CI, 7.1-8.3). Generally, a 65-year-old person in the United States would be expected to live for 19 more years.
The authors acknowledged the study’s limitations, including reliance on administrative claims data, subsequent misclassification of RA-ILD status, a lack of information on cause of death, and an underestimation of mortality caused by the inability to link all patients to the Social Security Administration Death Index.
The study was funded by Genentech and F. Hoffmann–La Roche. No other conflicts of interest were reported.