Background: Rheumatoid arthritis-associated interstitial lung disease (RA-ILD) is a severe extra-articular manifestation and a leading cause of premature mortality in RA. While historically viewed as a rare, late-stage complication, recent prospective studies using universal HRCT screening have identified RA-ILD in up to 11% of patients with early RA [1]. Until recently, detection of ILD in patients with RA relied mainly on respiratory symptoms. The 2023 ACR/CHEST and 2025 EULAR/ERS guidelines for connective tissue disease-associated ILD suggest a shift toward risk-stratified screening [2,3]. However, given that RA is a common disease where most patients exhibit ILD risk factors, broad screening implementation poses a risk of overwhelming radiological resources. Consequently, establishing the prevalence of clinically detected RA-ILD is essential to define the “diagnostic gap” associated with the traditional symptom-based model.

Objectives: To determine the prevalence, characteristics and excess mortality of clinically detected RA-ILD in a large multicenter cohort, and to quantify the “diagnostic gap” between routine practice and screening-based estimates.

Methods: We conducted a ten-year (Jan 2015 to Dec 2024) multicenter, retrospective quality assurance audit across five major Norwegian rheumatology departments (University Hospital of North Norway, St. Olavs Hospital, Levanger Hospital, Lillehammer Hospital for Rheumatic Diseases and Haukeland University Hospital). These departments represent each of the four health regions in Norway, with combined catchment areas of approximately 30% (1.7 million) of the Norwegian population.

Potential RA-ILD cases were identified using combined RA (M05/M06) and ILD (J84/J99) ICD-10 codes. All identified cases underwent manual chart review to verify both the RA and the RA-ILD diagnosis. During the review, we extracted radiographic patterns from HRCT images, dates of diagnosis, ERS/EULAR RA-ILD risk factors and vital status.

The total RA background population (denominator) was identified from a national registry using a previously validated ICD-10 based algorithm, including all patients residing in municipalities in the participating departments´ catchment areas. Moreover, a 3:1 control group matched for age and sex was sampled from the total RA population to assess excess mortality. Differences were assessed using the Chi-square test.

Results: The audit identified 162 verified RA-ILD cases within a total RA population of 12,223. Thus, the overall point prevalence of clinically detected RA-ILD was 1.3%, ranging from 1.0% to 1.6% in different health regions (Figure 1). The RA-ILD cohort exhibited a high-risk phenotype: 93.8% were seropositive (RF and/or ACPA), 75.9% had a smoking history and 52.8% were male (Table 1). The mean age at RA diagnosis was 59.7 years and the mean time to ILD diagnosis was 8.0 years. Radiographically, 95 (58.6%) had a usual interstitial pneumonia (UIP) pattern, 31 (19.1%) were indeterminate for UIP and 23 (14.2%) demonstrated a nonspecific interstitial pneumonia (NSIP) pattern. All-cause mortality during the ten-year study period was 35.8% in the RA-ILD cohort compared to 18.5% in the age-, sex- and geography-matched control group (p<0.0001).

Conclusions: In this multicenter audit, the prevalence of clinically detected RA-ILD was 1.3%, representing ~12% of expected cases. Current clinical strategies relying on respiratory symptoms rather than risk factor-based screening identify a more severe phenotype, defined by a high prevalence of UIP and associated with high mortality. These findings quantify a profound diagnostic gap in routine care and support the implementation of earlier, risk-stratified screening to detect early, treatable disease.

Figure 1.

Geographic variation in the prevalence of clinically detected RA-ILD across health regions in Norway

REFERENCES: [1] McDermott GC, Gill R, Byrne S, Gagne S, Wang X, Paudel ML, et al. Risk factors for interstitial lung disease in early rheumatoid arthritis and external validation of screening strategies: a cross-sectional analysis of the prospective SAIL-RA cohort in the USA. Lancet Rheumatol. 2025;7:e851–63.

[2] Johnson SR, Bernstein EJ, Bolster MB, Chung JH, Danoff SK, George MD, et al. 2023 American College of Rheumatology (ACR)/American College of Chest Physicians (CHEST) Guideline for the Screening and Monitoring of Interstitial Lung Disease in People with Systemic Autoimmune Rheumatic Diseases. Arthritis Rheumatol. 2024;76:1201–13.

[3] Antoniou KM, Distler O, Gheorghiu AM, Moor CC, Vikse J, Bizymi N, et al. ERS/EULAR clinical practice guidelines for connective tissue diseases associated interstitial lung disease. Ann Rheum Dis. 2025;S0003-4967(25)04320-1.

Acknowledgments: NIL.

Disclosure of Interests: Eirik Ikdahl Boehringer Ingelheim, Benedikte Døskeland: None declared, Liv Turid Bertelsen Boehringer Ingelheim, Gunnstein Bakland Boehringer Ingelheim, Tina Therese Pedersen Boehringer Ingelheim, Hu Yi Boehringer Ingelheim, Phuong Phuong Diep: None declared, Lene Maria Sundbakk: None declared, Sella Aarrestad Provan: None declared, Anna-Maria Hoffmann-Vold Boehringer Ingelheim, Janssen, Medscape, Merck Sharp & Dohme, Novartis, Roche, AbbVie, Avalyn, Astra Zeneca, Boehringer Ingelheim, Bristol Myers Squibb, Calluna Pharma, Genentech, Janssen, Medscape, Merck Sharp & Dohme, Pliant, Roche, Werfen, Astra Zeneca, Boehringer Ingelheim, Janssen.