Background/Purpose: Interstitial lung disease (ILD) is commonly associated with rheumatoid arthritis (RA) and can have significant morbidity and mortality. The objective was to calculate the prevalence, incidence and healthcare costs of RA-related ILD (RA-ILD) in the US.

Methods: We used data from the MarketScan Commercial and Medicare Supplemental Databases from 2004-2013. In each year, patients meeting 1 of the following criteria were considered to have RA-ILD: (A) ≥2 claims with a diagnosis of pulmonary fibrosis (ICD-9-CM 515, 516.3, 516.31) or rheumatic lung disease (ICD-9-CM 714.81) plus ≥2 claims with a diagnosis of rheumatoid arthritis (ICD-9-CM 714.xx excluding 714.3x and 714.4x) or (B) ≥2 claims with a diagnosis for rheumatic lung disease. Patients with 6 months of continuous enrollment prior to first RA-ILD diagnosis in the database and with no claims for pulmonary fibrosis or rheumatic lung disease during that period were classified as incident patients. Patients with evidence of other lung diseases were excluded. Demographic characteristics were measured on date of first RA-ILD diagnosis and clinical characteristics were based on diagnosis, procedure, and drug codes on claims over 12 months for patients who had 12 months of enrollment. All-cause healthcare resource utilization and costs were calculated over 5 years for incident patients with sufficient enrollment. All-cause mortality was assessed for patients who could be linked to Social Security Administration death data.

Results: Prevalence of RA-ILD ranged from 3.2 to 6.0 cases per 100,000 people (Table 1) and incidence ranged from 2.7 to 3.8 cases per 100,000 people. Mean age was 64-66 years across study years; the majority of patients were female (66%-70%). Common comorbidities included gastro-esophageal reflux disease (46%-54%), dyslipidemia (35%-52%), acute bronchitis/pneumonia (34%-38%), and hypertension (41%-61%). The majority of patients had a chest computed tomography (CT) scan (50%-59%) or chest x-ray (69%-80%) over a 12 month period. There were 750 incident patients with 5-year follow-up data; Over 5 years, 72% had an inpatient admission and 76% had an emergency room visit. Mean total 5-year costs were $173,405 per patient (SD $158,837). Annual per-patient costs were highest in years 1 and 5 (Table 2). At 5 years after first diagnosis in the data, 66.7% of patients were alive.

Conclusion: Prevalence of RA-ILD increased over time. For patients who could be followed over a 5-year period, utilization and costs were somewhat stable over time, although inpatient admissions were more common and costs were higher in year 1.

Table 2.