# Quantitative CT analysis in interstitial pneumonia with autoimmune features: diagnostic and prognostic insights from a retrospective cohort study

## TL;DR

This study uses quantitative CT scans to better understand and distinguish interstitial pneumonia with autoimmune features from other lung diseases, offering new diagnostic and prognostic insights.

## Contribution

The study introduces threshold-based quantitative CT as a reproducible method for diagnosing and predicting outcomes in interstitial pneumonia with autoimmune features.

## Key findings

- IPAF showed higher lung consolidation compared to CTD-ILD and a lower GGO-to-consolidation ratio.
- Higher GGO-to-consolidation ratios and emphysema percentage were linked to reduced disease progression risk in IPAF.
- QCT features like consolidation and GGO-to-consolidation ratio help differentiate IPAF from other ILD subtypes.

## Abstract

The position of interstitial pneumonia with autoimmune features (IPAF) within the interstitial lung disease (ILD) spectrum remains unclear, with limited data regarding quantitative CT (QCT). This study aims to evaluate threshold-based QCT for distinguishing IPAF from other ILD subtypes and to assess the prognostic value of specific QCT features.

In this retrospective single-centre study, 227 patients (mean age 63.6 ± 12.8 years) with CTD-ILD (n = 123), IPAF (n = 54), or IPF (n = 50) diagnosed between January 2005 and October 2024 were included. QCT assessed ground-glass opacity (GGO), consolidation, emphysema, affected lung, and GGO-to-consolidation ratio. Group comparisons used adjusted general linear models; progression-free survival (PFS) was analyzed with Kaplan–Meier and Cox regression to identify QCT-based risk factors.

Lung consolidation was significantly higher in IPAF than in CTD-ILD (p = 0.046), while CTD-ILD showed higher GGO-to-consolidation ratios than IPAF (p < 0.001) and IPF (p = 0.009). IPAF had shorter PFS than CTD-ILD but longer than IPF. Higher GGO-to-consolidation ratios (HR 0.87, 95% CI: 0.79–0.97, p = 0.011) and higher emphysema percentage (HR 0.96, 95% CI: 0.93–0.99, p = 0.011) were associated with reduced progression risk, whereas the usual interstitial pneumonia pattern with higher risk in some lung compartments (e.g., lower third, HR 1.70, 95% CI: 1.07–2.71, p = 0.024). In the exploratory subgroup analysis, the GGO-to-consolidation ratio was associated with lower PFS in CTD-ILD only.

IPAF more closely resembled IPF in QCT features. The GGO-to-consolidation ratio emerged as a potential discriminative and prognostic factor.

Threshold-based QCT provides reproducible diagnostic and prognostic biomarkers that help distinguish IPAF from other ILD subtypes and support risk stratification.

Quantitative CT (QCT) has not been systematically investigated in interstitial pneumonia with autoimmune features (IPAF).QCT revealed distinct imaging and prognostic differences when comparing IPAF with other interstitial lung disease subtypes.QCT provides reproducible imaging biomarkers that aid IPAF differentiation and support clinical risk stratification.

Quantitative CT (QCT) has not been systematically investigated in interstitial pneumonia with autoimmune features (IPAF).

QCT revealed distinct imaging and prognostic differences when comparing IPAF with other interstitial lung disease subtypes.

QCT provides reproducible imaging biomarkers that aid IPAF differentiation and support clinical risk stratification.