COUNTERPOINT: Does Interstitial Pneumonia With Autoimmune Features Represent a Distinct Class of Patients With Idiopathic Interstitial Pneumonia? No

Review: Serum Biomarkers of Lung Fibrosis in Interstitial Pneumonia with Autoimmune Features-What Do We Already Know?

Interstitial pneumonia with autoimmune features (IPAF) belongs to a group of diseases called interstitial lung diseases (ILDs), which are disorders of a varied prognosis and course. Finding sufficiently specific and sensitive biomarkers would enable the progression to be predicted, the natural history to be monitored and patients to be stratified according to their treatment. To assess the significance of pulmonary fibrosis biomarkers studied thus far, we searched the PubMed, Medline and Cochrane Library databases for papers published between January 2015 and June 2021. We focused on circulating biomarkers. A primary review of the databases identified 38 articles of potential interest. Overall, seven articles fulfilled the inclusion criteria. This review aims to assess the diagnostic and prognostic value of molecules such as KL-6, SP-A, SP-D, circulating fibrocytes, CCL2, CXCL13, CXCL9, CXCL10 and CXCL11. All of these biomarkers have previously been studied in idiopathic pulmonary fibrosis (IPF) and connective tissue disease-associated interstitial lung disease (CTD-ILD). IPAF is a disorder of a heterogeneous nature. It explains the lack of coherent observations in terms of correlations with functional parameters. There is still no meta-analysis of pulmonary fibrosis biomarkers in IPAF. This is mainly due to the heterogeneity of the methodology and groups analysed in the research. More research in this area is needed.

Interstitial pneumonia with autoimmune features: from research classification to diagnosis

PURPOSE OF REVIEW

The term interstitial pneumonia with autoimmune features (IPAF) was first proposed by an international task force in 2015 as a research classification to standardise nomenclature regarding patients with idiopathic interstitial pneumonia and features of connective tissue disease. However, how the use of this term and its proposed definition translates to clinical practice remains uncertain. This review will provide a comprehensive overview of studies of IPAF cohorts to date, discuss the consideration of IPAF as a distinct diagnostic entity and outline a suggested approach to patient management.

RECENT FINDINGS

Considerable heterogeneity exists between published IPAF cohorts, with some cohorts exhibiting similarities to those with connective tissue disease-associated interstitial lung disease (CTD-ILD), and others more similar to idiopathic interstitial pneumonias including idiopathic pulmonary fibrosis (IPF). Little data exist to inform the management of patients who fulfil the IPAF criteria. Preliminary data supports pragmatic management of these patients as having a working clinical diagnosis of either idiopathic interstitial pneumonia or CTD-ILD. Future research studies into this approach are required.

SUMMARY

The term IPAF, and its definition, have been of fundamental benefit to facilitating research in this diverse patient group. However, to date, there remain many unanswered questions regarding their natural histories and response to treatment.

Clinical, radiologic and serologic profile of patients with interstitial pneumonia with autoimmune features: a cross-sectional study

The current study aimed to characterize patients from a rheumatology referral center in north India, who satisfied the definition of interstitial pneumonia with autoimmune features (IPAF) as given by the American Thoracic Society and European Respiratory Society (ATS/ERS) consensus committee in 2015. Thirty-five adult patients aged 18 years and above, fulfilling the 2015 ATS/ERS criteria for IPAF were included in the study. The clinical and immunological profile, and radiologic findings on high-resolution computerized tomography thorax were noted. Antinuclear antibody (ANA) by indirect immunofluorescence at 1:320 titer and myositis-specific antibody (MSA) assays were performed. Non-parametric tests were used to compare variables between groups. The study cohort included predominantly female patients with a mean age of 50.6 ± 13 years and mean duration of disease of 38.8 ± 28.4 months. Majority of patients (49%) fulfilled the morphologic and serologic domains as per the IPAF consensus criteria and 31% patients had features in all three domains. Non-specific interstitial pneumonia was the most common pattern observed in 77% patients. Raynaud’s phenomenon and inflammatory arthritis were the predominant autoimmune features. Pulmonary arterial hypertension was documented in 60% of patients on echocardiography. Positive ANA at 1:320 dilution was present in all 26 patients tested, whereas extractable nuclear antigen and MSA assays detected autoantibodies in 49% and 51% of patients respectively. IPAF predominantly affected females in the age group of 50 years and above, with varied autoimmune manifestations and autoantibody profile.

Interstitial Pneumonia with Autoimmune Features: Why Rheumatologist-Pulmonologist Collaboration Is Essential

In 2015 the European Respiratory Society (ERS) and the American Thoracic Society (ATS) “Task Force on Undifferentiated Forms of Connective Tissue Disease-associated Interstitial Lung Disease” proposed classification criteria for a new research category defined as “Interstitial Pneumonia with Autoimmune Features” (IPAF), to uniformly define patients with interstitial lung disease (ILD) and features of autoimmunity, without a definite connective tissue disease. These classification criteria were based on a variable combination of features obtained from three domains: a clinical domain consisting of extra-thoracic features, a serologic domain with specific autoantibodies, and a morphologic domain with imaging patterns, histopathological findings, or multicompartment involvement. Features suggesting a systemic vasculitis were excluded. Since publication of ERS/ATS IPAF research criteria, various retrospective studies have been published focusing on prevalence; clinical, morphological, and serological features; and prognosis of these patients showing a broad heterogeneity in the results. Recently, two prospective, cohort studies were performed, confirming the existence of some peculiarities for this clinical entity and the possible progression of IPAF to a defined connective tissue disease (CTD) in about 15% of cases. Moreover, a non-specific interstitial pneumonia pattern, an anti-nuclear antibody positivity, and a Raynaud phenomenon were the most common findings. In comparison with idiopathic pulmonary fibrosis (IPF), IPAF patients showed a better performance in pulmonary function tests and less necessity of oxygen delivery. However, at this stage of our knowledge, we believe that further prospective studies, possibly derived from multicenter cohorts and through randomized control trials, to further validate the proposed classification criteria are needed.

Myositis-specific Antibodies Identify A Distinct Interstitial Pneumonia with Autoimmune Features Phenotype

Interstitial pneumonia with autoimmune features (IPAF) characterises individuals with interstitial lung disease (ILD) and features of connective tissue disease (CTD) who fail to satisfy CTD criteria. Inclusion of myositis-specific antibodies (MSAs) in the IPAF criteria has generated controversy, as these patients also meet proposed criteria for an anti-synthetase syndrome. Whether MSAs and myositis associated antibodies (MAA) identify phenotypically distinct IPAF subgroups remains unclear.A multi-center, retrospective investigation was conducted to assess clinical features and outcomes in patients meeting IPAF criteria stratified by the presence of MSAs and MAAs. IPAF subgroups were compared to cohorts of patients with idiopathic inflammatory myopathy-ILD (IIM-ILD), idiopathic pulmonary fibrosis (IPF) and non-IIM CTD-ILDs. The primary endpoint assessed was three-year transplant-free survival. Two hundred sixty-nine patients met IPAF criteria, including 35 (13%) with MSAs and 65 (24.2%) with MAAs. Survival was highest among patients with IPAF-MSA and closely approximated those with IIM-ILD. Survival did not differ between IPAF-MAA and IPAF without MSA/MAA cohorts. Usual interstitial pneumonia (UIP) morphology was associated with differential outcome risk, with IPAF patients with non-UIP morphology approximating survival observed in non-IIM CTD-ILDs. MSAs, but not MAAs identified a unique IPAF phenotype characterised by clinical features and outcomes similar to IIM-ILD. UIP morphology was a strong predictor of outcome in others meeting IPAF criteria. Because IPAF is a research classification without clear treatment approach, these findings suggest MSAs should be removed from the IPAF criteria and such patients should be managed as an IIM-ILD.