Background/Purpose: The term interstitial pneumonia with autoimmune features (IPAF) has recently been proposed to identify those patients with ILD and clinical and/or serological autoimmune manifestations who do not meet diagnostic criteria for a specific CTD (UCTD-ILD). Our aim was to re-classify our patients with ILD and features of CTD according to the 2015 European Respiratory Society/American Thoracic Society research statement proposed criteria for IPAF and examine their applicability in clinical practice. We also evaluate other clinical tools which might improve their specificity.

Methods: Retrospective review of medical records of 100 patients with ILD attending the multidisciplinary Pulmonary and Rheumatology clinic at our centre between 2011 and 2016. Fulfilment of the proposed IPAF criteria was assessed in all patients who did not meet current criteria for a definite CTD. Additional autoimmune/inflammatory data not included in the IPAF domains, as well as nailfold capillaroscopy findings (available in 47 patients), were also recorded. Analysis was carried out with non-parametric tests and significance laid at 95%.

Results: We identified 62 CTD-ILD, 26 IPAF and 12 non-IPAF patients, with 71% women. Therefore, 68% (26/38) of patients previously regarded as UCTD-ILD were captured by the IPAF criteria. Age at onset was higher in patients from the non-IPAF group (p<0.01). Definite or possible Usual Interstitial Pneumonia (UIP) and Non-Specific Interstitial Pneumonia (NSIP) were found in 41% and 40% of patients, respectively. A non-UIP morphologic pattern predominated in CTD-ILD patients (58%), while NSIP was more frequent than UIP in IPAF (46% versus 27%) and UIP predominated in non-IPAF (67%). Pulmonary hypertension and vasculopathy were associated to UIP (p<0.05). Coexistent hypersensitive pneumonitis was marginally more frequent in IPAF and non-IPAF than in CTD-ILD. There was a 72% of ANA+ and 37% RF+ patients with no differences among groups. In contrast, ACPA and dsDNA were found in 0 but only in 1 non-IPAF case. Interestingly, two patients with antisynthetase antibodies fulfilled both the preliminary criteria for antisynthetase syndrome and for IPAF. As regards items included in the IPAF clinical domain, RP was present in 27% (6/22) of IPAF patients and only in 1 non-IPAF. No differences were found for arthritis or RP between IPAF and non-IPAF. Capillaroscopy changes were found in 67% (8/12) and 50% (6/12) of non-IPAF and IPAF patients, respectively. Haemolytic anemia, high CRP and LDH, hyperferritinemia and hypertriglyceridemia were associated to a fatal outcome (p<0.05), with no differences between groups.

Conclusion: We found few phenotype differences between patients re-classified as IPAF and those with non-IPAF according to the new criteria. This indicates that the proposed IPAF criteria might not be able to capture all patients with inflammatory and/or isolated features of CTD. In addition, only some of the proposed items for IPAF were prevalent in patients with UCTD-ILD, being the presence of RP a dominant one. The use of capillaroscopy could therefore help characterize a set of patients with UCTD-ILD. Prospective and larger cohorts are needed to confirm these findings.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/utility-of-interstitial-pneumonia-with-autoimmune-features-ipaf-proposed-criteria-in-the-classification-of-patients-with-ctd-associated-interstitial-lung-disease-in-a-single-centre/