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. 2017 Jun:127:51-56.
doi: 10.1016/j.rmed.2017.04.012. Epub 2017 Apr 22.

The performance of the GAP model in patients with rheumatoid arthritis associated interstitial lung disease

Julie Morisset  1 , Eric Vittinghoff  2 , Bo Young Lee  3 , Roberto Tonelli  4 , Xiaowen Hu  5 , Brett M Elicker  6 , Jay H Ryu  5 , Kirk D Jones  7 , Stefania Cerri  4 , Andreina Manfredi  8 , Marco Sebastiani  8 , Andrew J Gross  9 , Brett Ley  9 , Paul J Wolters  9 , Talmadge E King Jr  9 , Dong Soon Kim  3 , Harold R Collard  9 , Joyce S Lee  10
Affiliations

The performance of the GAP model in patients with rheumatoid arthritis associated interstitial lung disease

Julie Morisset et al. Respir Med. 2017 Jun.

Abstract

Background: Rheumatoid arthritis-associated interstitial lung disease (RA-ILD) is associated with significant morbidity and mortality. Similarities have been observed between patients with idiopathic pulmonary fibrosis (IPF) and the UIP (usual interstitial pneumonia) form of RA-ILD. The GAP (gender, age, physiology) model has been shown to predict mortality in patients with IPF, but its ability to predict mortality in RA-ILD is not known.

Methods: We identified 309 patients with RA-ILD at 4 academic centers with ongoing longitudinal cohorts of patients with ILD. The primary endpoint was mortality. To handle missing data (n = 219 subjects with complete dataset), multiple imputation by iterative chained equations was used. Using the GAP model as a baseline, we assessed improvements in mortality risk prediction achieved by incorporating additional variables. Model discrimination was assessed using the c-index, and calibration was checked by comparing observed and expected incidence of death.

Results: Patients had a mean age of 65 years and were predominantly female (54%). The mean forced vital capacity (FVC) % predicted was 73 and the mean diffusing capacity for carbon monoxide (DLCO) % predicted was 55. Twenty-four percent of the 236 patients with a high-resolution computed tomography scan available for review had a definite UIP pattern. The original GAP model, including gender, age, FVC%, and DLCO%, had a c-index of 0.746 in our cohort. Calibration of this model was satisfactory at 1, 2 and 3 years. Model discrimination was not meaningfully improved by adding other clinical variables.

Conclusion: The GAP model that was derived for IPF performs similarly as a mortality risk prediction tool in RA-ILD.

Keywords: Interstitial lung disease; Prognosis; Rheumatoid arthritis; Risk assessment.

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Figures

Figure 1
Figure 1
Cohort formation Patients were excluded if they did not have interstitial lung disease on high-resolution computed tomography and/or surgical lung biopsy
Figure 2
Figure 2
Cumulative mortality in the imputed dataset by risk category.
See this image and copyright information in PMC

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