Background/Purpose:  Interstitial lung disease (ILD) is associated with substantial morbidity in rheumatoid arthritis (RA), but virtually nothing is known about the long-term of progression of pulmonary disease.

Methods:  All patients with RA-ILD (ACR 1987 criteria for RA) seen at a single center from 1998-2014 with at least 4 weeks follow-up and at least 1 pulmonary function test (PFT) were identified and manually screened for study inclusion. Follow-up data were abstracted until death, 10 years follow-up or December 31, 2015, including all PFTs within 12 months of initial diagnosis and first PFT for each subsequent follow-up year. Progression was defined as a diffusing capacity for carbon monoxide (DLCO) < 40% predicted/ too ill to perform DLCO or a forced vital capacity (FVC) < 50% predicted. Time to progression was analyzed using Kaplan-Meier methods and Cox models adjusted for age and sex.

Results: Of the 167 included patients, 81 (49%) female, 97% Caucasian, mean age was 67 years (±10) at ILD diagnosis. 62 (37%) were never smokers. Median follow-up time from ILD diagnosis was 3.3 (range 0.01-14.8) years. Eighty-nine (53%) had usual interstitial pneumonia (UIP), 70 (42%) had non-specific interstitial pneumonia (NSIP), and 8 (5%) had RA-related organizing pneumonia (OP). A total of 564 PFTs were abstracted. Baseline PFTs at time of ILD diagnosis (± 6 months) included mean percent predicted FVC of 72% ± 20, forced expiratory volume (FEV1) of 72% ±21, total lung capacity (TLC) of 73% ± 16 and DLCO of 55% ±18. Mean percent predicted DLCO for UIP was 51% ±16, for NSIP 58% ±20, and for OP 74% ±13 (P=0.006). During follow-up, DLCO declined to <40% predicted or were too ill to perform the test in 57 patients, and 29 patients developed an FVC < 50%. By 5 years after ILD diagnosis, 33.2% of patients reached DLCO<40% predicted or were too ill to perform the test and 16.3% of patients reached FVC<50% predicted. Risk factors for progression to DLCO < 40% were UIP (vs NSIP) (hazard ratio [HR]: 2.22; 95% confidence interval [CI]: 1.26, 3.92) and male sex (HR: 1.63; 95% CI: 0.96, 2.75). C-reactive protein at ILD diagnosis was associated with progression to FVC<50% (HR: 1.16 per 10 mg/L increase; 95% CI: 0.97, 1.38). Higher percent predicted DLCO and FVC at baseline reduced the risk for progression to a DLCO < 40% (HR: 0.48 per 10 unit increase; 95% CI: 0.40, 0.58; HR: 0.70 per 10 unit increase; 95% CI: 0.60, 0.82; respectively) and an FVC < 50% (HR: 0.64 per 10 unit increase; 95% CI: 0.48, 0.84; HR: 0.38 per 10 unit increase; 95% CI: 0.29, 0.50; respectively). Estimated rate of change in the first 6 months for FVC was a median increase of 1.0% predicted (interquartile range: -5.0, 7.0) and for DLCO was a median loss of 1.0% (interquartile range: -6.0, 5.0). There was a significant association between the DLCO 6-month rate of change progression to DLCO < 40% (HR: 1.55 per 10-unit decrease; 95% CI: 1.10, 2.18) and between the FVC 6-month rate of change and progression to FVC<50% (HR: 2.44; 95% CI: 1.44, 4.13).

Conclusion: Progressive loss of pulmonary function is common in RA-ILD and is typically worse in patients with UIP than NSIP. A higher baseline DLCO and FVC reduced the risk of progression, but higher rates of change in the first 6 months increased the risk of severe pulmonary impairment.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/progressive-decline-of-lung-function-in-rheumatoid-arthritis-associated-interstitial-lung-disease/