The incidental discovery of interstitial lung abnormalities (ILAs) became increasingly recognized on low-dose CT scan lung cancer screening tests and has led to further research to understand the clinical implications of this condition. The original definition of “interstitial lung abnormality” was described in the Fleischner Society position paper in 2020: incidental nondependent bilateral parenchymal abnormalities (including ground glass or reticular abnormalities, lung distortion, traction bronchiectasis, honeycombing, and nonemphysematous cysts) involving at least 5% of a lung zone and excluding high-risk populations.1
After the delineation was made between ILA and interstitial lung disease (ILD), which is based on respiratory symptoms, disease burden on high-resolution CT scan, and pulmonary function impairment, the Fleischner Society created recommendations regarding monitoring and follow-up. Identifying ILAs is important, as a portion of ILAs will progress over time. Whether the specific ILA has increased risk features of progression, risk factor reduction is recommended for all groups. Serial pulmonary function testing and CT scans are recommended for ILA subtypes with features indicating progression.
Building on the aforementioned position paper, the American Thoracic Society (ATS) released a clinical statement in May 2025, “Approach to the Evaluation and Management of Interstitial Lung Abnormalities.”2 A committee of experts voted on 11 questions. The updated definition of ILA contains similar CT scan criteria as listed previously; however, these new guidelines now remove the need for the findings to be incidental and also exclude high-risk populations, which are those with rheumatoid arthritis, scleroderma, occupational exposure, or familial ILD. The committee agreed with the previous notion of stratifying ILAs into three main subcategories, including nonsubpleural ILAs, subpleural nonfibrotic ILAs, and subpleural fibrotic ILAs, due to the prognostic significance of each category. Overall, more than half of those with ILAs experience radiologic progression over five years with clinical worsening and reduction in exercise capacity, and approximately 10% of ILAs progress to ILD annually.
ATS formulated recommendations based on prespecified population intervention control outcome (PICO) questions regarding screening and diagnosis, a baseline assessment, and a follow-up assessment. Screening for detection of ILAs was recommended in the lung cancer screening-eligible population, in those with a connective tissue disease, and in adults over 50 years old who have a first-degree relative with familial pulmonary fibrosis. If incidental ILAs are discovered, follow-up should include a baseline assessment of symptoms and pulmonary function testing. If ILAs are identified, follow-up imaging would include a CT scan every 12 months for high-risk populations* or every two to three years if considered low-risk. The reason for this is to identify progression to ILD, which would warrant additional treatment and management. Recommendations were made against lung biopsy, testing for mucin 5B, or telomere length in evaluating ILAs. Future research needs include the roles of nonpharmacologic and pharmacologic interventions when ILAs are discovered, so screening and monitoring would be of greater benefit if relevant clinical outcomes were possible.
*High-risk populations: smoking history, family history of pulmonary fibrosis, connective tissue disease, occupational exposures
References
1. Hatabu H, Hunninghake GM, Richeldi L, et al. Interstitial lung abnormalities detected incidentally on CT: A position paper from the Fleischner Society. Lancet Respir Med. 2020;8(7):726-737. doi:10.1016/S2213-2600(20)30168-5
2. Podolanczuk AJ, Hunninghake GM, Wilson KC, et al. Approach to the evaluation and management of interstitial lung abnormalities: An official American Thoracic Society clinical statement. Am J Respir Crit Care Med. 2025;211(7):1132-1155. doi:10.1164/rccm.202505-1054ST
