Interstitial pneumonia with autoimmune features (IPAF) describes patients with interstitial lung disease and autoimmunity who do not meet classification criteria for a systemic autoimmune rheumatic disease, including systemic lupus erythematosus (SLE). We aimed to determine whether the criteria developed by the European Alliance of Association of Rheumatology and American College of Rheumatology (EULAR/ACR) would classify more patients with IPAF as SLE, than those developed by the Systemic Lupus International Collaborating Clinics (SLICC). Increasing the recognition of SLE among patients with IPAF may affect therapy.

This observational, retrospective, single-center cohort study included consecutive patients initially classified as having IPAF between December 2005-August 2019. We reviewed patients’ charts to assess whether more patients met SLE criteria by SLICC or EULAR/ACR methodology. Fisher’s exact test assessed the significance of the difference in the proportion of patients classified by the two criteria.

We included 201 patients initially classified as IPAF. Twelve were identified as SLE by SLICC criteria and 23 by EULAR/ACR criteria. All but three patients with lymphopenia who met SLE criteria by SLICC also met it by EULAR/ACR. The difference in the proportion of IPAF patients meeting SLE criteria by the two methods was statistically significant (p < 0.001).

Patients with IPAF were classified as SLE more frequently using EULAR/ACR criteria than by SLICC criteria. The EULAR/ACR criteria may be superior for SLE classification in patients with ILD. Patients with IPAF and SLE features should undergo full work-up to evaluate for SLE classification as it may affect therapy.