Decoding IPAF: When Lung Disease Mimics Autoimmunity
"Understanding Interstitial Pneumonia with Autoimmune Features (IPAF) for Better Diagnosis and Care"
Interstitial lung diseases (ILDs), also known as diffuse parenchymal lung diseases (DPLDs), can sometimes overlap with autoimmune conditions, creating diagnostic challenges. One such overlap is seen in Interstitial Pneumonia with Autoimmune Features (IPAF), where patients exhibit lung disease alongside autoimmune markers but don't meet the criteria for a defined connective tissue disease (CTD). This article unpacks the concept of IPAF, its diagnostic criteria, and what it means for treatment.
Recognizing a potential connective tissue disease in ILD cases is crucial because the prognosis and treatment approaches differ significantly. Connective tissue disease-related ILDs (CTD-ILDs) often have a more favorable prognosis compared to idiopathic pulmonary fibrosis (IPF), and treatment typically involves corticosteroids and immunosuppressants.
Sometimes, lung involvement is the first sign of an underlying CTD, highlighting the importance of thorough clinical evaluation for autoimmune features in ILD patients. These features are more commonly found in women under 50. Imaging and histological findings, such as nonspecific interstitial pneumonia (NSIP), organizing pneumonia (OP), or lymphoid interstitial pneumonia (LIP), can also suggest an underlying CTD.
IPAF Within the ILD Landscape
Interstitial pneumonia with autoimmune features (IPAF) is a subset of interstitial lung disease in which autoimmune features are present but criteria for a defined rheumatic disease are not met. Classification requires interstitial pneumonia and features from at least two of three domains. ILD is a serious manifestation of autoimmune rheumatic diseases, although its prevalence varies among individual diseases and it remains an important cause of morbidity and mortality.
A Retrospective Look at Autoimmune ILD
A 2019 report described a retrospective, descriptive, single-center study of patients with autoimmune forms of interstitial lung disease. The patients were evaluated between February 2008 and August 2014, with data extracted from electronic medical records. The study examined phenotypic characteristics and natural history, including longitudinal changes in forced vital capacity.
What Defines IPAF? The 2015 Classification
In 2015, the American Thoracic Society and the European Respiratory Society proposed new criteria to standardize the definition of IPAF. This was an attempt to better characterize this patient group and facilitate research into their long-term prognosis.
- Presence of ILD on imaging (CT scan) or surgical lung biopsy.
- Exclusion of other known causes of ILD after careful evaluation.
- Absence of sufficient criteria for a defined connective tissue disease.
- Presence of at least one feature from two of the following domains: clinical, biological, or morphologic.
Open Questions in IPAF Management
A review of IPAF summarizes the current state of knowledge and discusses data that inform management decisions for patients meeting IPAF criteria. It also highlights important questions for future research. The available source description does not specify particular treatment failures or resolve those questions.
A Research Classification, Not a Defined Rheumatic Disease
IPAF is described as a research classification for people with idiopathic interstitial pneumonia whose clinical, serologic, and/or imaging features are consistent with an autoimmune process, but who do not meet criteria for a defined systemic autoimmune rheumatic disease. The classification criteria were established in 2015. Research since then has examined IPAF, though the supplied source descriptions do not provide specific comparative outcomes.
The Future of IPAF: Research and Personalized Care
While the IPAF classification is a step forward, questions remain about the exhaustiveness and relevance of the criteria. Some clinicians argue that other clinical signs, such as esophageal dysmotility or muscle weakness, should be included. Additionally, the prognostic implications of IPAF are still being studied.
Clarifying Prognosis and Terminology
A systematic review and meta-analysis set out to clarify IPAF prognosis and prognostic factors in comparison with idiopathic pulmonary fibrosis (IPF) and connective tissue disease-associated interstitial lung disease. Separately, a review reports that an international task force first proposed the term IPAF in 2015 as a research classification. Its stated purpose was to standardize nomenclature for idiopathic interstitial pneumonia with features of connective tissue disease.
Research Needs in Autoimmune-Associated ILD
A 2025 article on autoimmune disease-associated interstitial lung disease reports that rapid progression and worsening pulmonary fibrosis can increase mortality risk and contribute to poor prognosis. Despite considerable research in the field, its authors identify a lack of bibliometric studies addressing global research. More broadly, ILDs are heterogeneous and have complex pathophysiology, posing challenges in clinical practice.
Lung Involvement Across Systemic Autoimmune Disease
Connective tissue disease-associated ILD occurs in autoimmune disorders including systemic sclerosis, Sjögren disease, systemic lupus erythematosus, and idiopathic inflammatory myopathies. The broader terms systemic autoimmune rheumatic diseases (SARDs) and SARD-ILD are increasingly used in guidelines. Interstitial lung disease is a common way autoimmune diseases affect the lungs, but the likelihood and severity of lung involvement vary among conditions.
Current treatment for IPAF is not standardized and is tailored to the individual patient, considering clinical, imaging, biological, and histopathological findings. Multidisciplinary discussion is essential to determine the best approach.
Ultimately, the IPAF classification helps standardize the definition of a distinct entity from IPF and CTD-related ILDs. Further research is needed to refine the criteria, evaluate long-term prognosis, and guide therapeutic interventions, leading to more personalized and effective care for patients with IPAF.