What is the expected annual decline in Forced Expiratory Volume in 1 second (FEV1) in patients with Rheumatoid Arthritis-Associated Interstitial Lung Disease (RA-ILD)?

Annual FEV1 Decline in Rheumatoid Arthritis-Associated Interstitial Lung Disease

Patients with Rheumatoid Arthritis-Associated Interstitial Lung Disease (RA-ILD) typically experience an annual FEV1 decline of 50-90 ml/year, which is significantly accelerated compared to the normal age-related decline of 29 ml/year in healthy nonsmokers. 1

Patterns of Lung Function Decline in RA-ILD

The decline in lung function in RA-ILD patients follows several distinct trajectories:

• Rapidly declining pattern (5% of patients): Characterized by steep FEV1 decline
• Slowly declining pattern (48.6% of patients): Most common trajectory
• Stable pattern (38.4% of patients): Minimal change over time
• Improving pattern (7.9% of patients): Small subset showing improvement 2

Risk Factors for Accelerated Decline

Several factors predict more rapid FEV1 decline in RA-ILD:

• Age ≥70 years: 10.8 times higher risk of rapid decline 2
• Early RA diagnosis (within preceding 2 years): 10.1 times higher risk 2
• Simultaneous diagnosis of RA and ILD (within 24 weeks): 9.18 times higher risk 2
• Greater extent of lung involvement on imaging: 3.28 times higher risk 2
• High titers of IgM rheumatoid factor: Associated with increased mortality 3

Clinical Context and Significance

• The American Thoracic Society defines normal FEV1 decline in healthy nonsmokers as approximately 29 ml/year 1
• Accelerated decline of 50-90 ml/year is associated with increased morbidity and mortality from chronic respiratory diseases 1
• A decline in FEV1 greater than 8% or 330 mL per year should be considered abnormal in working adults 4
• Progressive fibrosing ILD (PF-ILD) is common in RA-ILD, affecting approximately 52% of patients 3

Monitoring Recommendations

For effective monitoring of RA-ILD progression:

• Initial frequency: Annual spirometry until progression rate is established 1
• Primary measurement: FEV1 should be the primary measurement used to assess longitudinal change, as it is less affected by technical factors than FVC 1
• Duration of follow-up: Longer follow-up periods (>5 years) improve the precision of estimated FEV1 decline rate 1
• Definition of significant decline: A decline of 15% or more in FEV1 from baseline (beyond expected age-related loss) is considered clinically significant 1

Pitfalls and Caveats

• Technical variability: Even with good spirometry programs, technical factors can contribute to variability in measurements 1
• Weight changes: Should be recorded during follow-up as weight gain can contribute to decline in lung function 1
• Short-term vs. long-term assessment: Short-term longitudinal changes (<5 years) may be difficult to interpret due to inherent FEV1 technical variability 1
• Disconnect between symptoms and function: Many RA-ILD patients (57/63 in one study) lack significant respiratory symptoms despite having HRCT and PFT abnormalities 5
• RA disease activity and lung function: Lung function trajectory does not necessarily correlate with RA disease activity trajectory 2

Understanding the expected rate of FEV1 decline in RA-ILD is crucial for early detection of disease progression and timely therapeutic intervention to improve outcomes.