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Abstract
Background Interstitial pneumonia with autoimmune features (IPAF) is a research classification proposed by the European Respiratory Society and American Thoracic Society Task Force for those patients with forms of interstitial lung disease (ILD) that have autoimmune features but that do not classify as having systemic rheumatic diseases such as systemic lupus erythematous (SLE). The IPAF classification is dynamic, as patients may evolve into specific autoimmune conditions such as rheumatoid arthritis, systemic lupus erythematosus, or dermatomyositis with specific therapeutic and prognostic implications. In 2019, the European Alliance of Association of Rheumatology/American College of Rheumatology (EULAR/ACR) published updated criteria for SLE with similar sensitivity but higher specificity than the 20122019 EULAR/ACR criteria had higher specificity than the 2012 Systemic Lupus International Collaborating Clinics (SLICC) criteria. The purpose of this study was to review data of patients classified as IPAF and test the hypothesis that the 2019 EULAR/ACR criteria will re- classify more of them as SLE-ILD.
Methods This observational, single-center cohort study included consecutive patients who had initially been classified as having IPAF between December 1st, 2005-August 31st, 2019. Two authors (GM-Z, EKJ) independently reviewed patients’ charts and assessed the subsequent development of SLE criteria by SLICC or 2019 EULAR/ACR classifications. Fisher’s exact test was used to assess for significant difference in number of patients meeting SLE criteria by SLICC criteria vs 2019 EULAR/ACR criteria.
Results A total of 197 patients that had been initially classified as IPAF were included. Out of these 197 patients, 12 met SLE criteria by SLICC and 23 by 2019 EULAR/ACR. All but three patients that met SLE criteria SLICC also met 2019 EULAR/ACR criteria. These difference in eligibility for this three patients was due to lymphopenia. The most frequent manifestations allowing patients to be classified as SLE by either criteria were ANA positivity, arthritis, and pericardial or pleural effusions. The difference in meeting SLE criteria between groups was statistically significant (p<0.001) (figure 1 and table 1).
Conclusion In 197 patients originally diagnosed with IPAF and followed for up to 18.5 yr., a classification of systemic lupus erythematosus could be made using SLICC criteria in 6.0% of patients and by 2019 EULAR/ACR criteria in 11.6% of patients. We suspect that ILD may be an under-recognized early manifestation of SLE. Patients with ILD who have features seen in SLE, particularly dsDNA/Smith, arthritis and serositis should undergo full work-up to evaluate for other SLE manifestations.
IPAF patients meeting SLE criteria by SLICC and 2019 EULAR/ACR
The figure shows the distribution of positive characteristics in patients meeting SLE criteria by A) SLICC and by B) 2019 EULAR/ACR. Note that characteristics that were not met by any patients were omitted from the figure. Ab=antibodies, SLE= systemic lupus erythematous
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