Background/Purpose:

Approximately 15-25% of patients diagnosed with idiopathic interstitial lung disease (ILD) have some features of autoimmunity, yet do not meet classification criteria for a systemic autoimmune rheumatic disease (ARD). In 2015, the American Thoracic Society (ATS) and European Respiratory Society (ERS) proposed the term “interstitial pneumonia with autoimmune features” (IPAF) to describe these patients. The natural history of IPAF with regard to its potential progression to an ARD is largely unknown. The aim of this study was to compare the risk of progression to an ARD between patients with IPAF and those with idiopathic ILD without autoimmune features.

Methods:

We performed a retrospective cohort study of patients with ILD who were evaluated at Columbia University Medical Center from 2009-2017. Data were extracted from the electronic medical record. Patients were identified using ICD-9 and ICD-10 codes for ILD. After excluding patients with ILD due to a secondary cause, the remaining patients were labeled “idiopathic ILD” and were divided into 2 categories based on the ATS/ERS classification criteria for IPAF: (1) those who met IPAF criteria and (2) those who did not meet IPAF criteria at initial ILD diagnosis. We then determined the percentage of patients with idiopathic ILD who were diagnosed with an ARD by a rheumatologist in the follow up period. We performed multiple logistic regression modeling the presence of IPAF at initial ILD diagnosis as the independent binary variable and diagnosis of an ARD in the follow up period as the dependent binary variable, controlling for age, sex, smoking status and immunosuppressive therapy.

Results:

Out of 650 patients with ILD who were screened, complete longitudinal data were available for 393 patients. Of these 393 patients, 225 had ILD due to a secondary cause (e.g., hypersensitivity pneumonitis, ARD, sarcoidosis) and 168 had idiopathic ILD at baseline. Of the 168 patients with idiopathic ILD, 48 met IPAF criteria at initial ILD diagnosis and 120 did not. Compared to patients without IPAF, those with IPAF were younger and a greater proportion (1) were female; (2) had positive autoantibodies; (3) had an NSIP pattern on HRCT; and (4) had pulmonary hypertension at initial ILD diagnosis. In the mean follow up period of 5.5 ± 3 years, 17% (8/48) of patients with IPAF were later diagnosed with an ARD compared to 2% (2/120) of patients without IPAF. In a multivariable model adjusted for age, sex, smoking status and immunosuppressive therapy, the odds of progressing to an ARD were 13 times higher in patients with IPAF than in those without IPAF (OR 13.3, 95% CI 1.3-130.5, p-value=0.03).

Conclusion:

Among patients with idiopathic ILD, IPAF confers a significantly higher risk of progression to an ARD. Prospective studies are needed to further characterize the natural history of IPAF.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/risk-of-progression-of-interstitial-lung-disease-with-autoimmune-features-to-a-systemic-autoimmune-rheumatic-disease/