Assessment of CT quantitative characteristics derived from CT in connective tissue disease-associated interstitial lung disease.

BACKGROUND: Connective tissue disease-associated interstitial lung disease (CTD-ILD) is a severe complication, yet early objective detection of pulmonary structural and microvascular alterations remains challenging. This study aimed to quantitatively compare pulmonary structural alterations between connective tissue disease (CTD) patients with and without interstitial lung disease (ILD) and to identify independent computed tomography (CT)-derived discriminators for ILD diagnosis by means of quantitative computed tomography (QCT).

METHODS: Fifty-one CTD patients with ILD (median age, 51 years; 66.7% female) and thirty-three CTD patients without ILD (median age, 33 years; 69.7% female) who underwent paired inspiratory and expiratory non-contrast chest computed tomography (CT) scans and pulmonary function testing were retrospectively collected. The lung density, functional small airway and pulmonary vessel parameters were analyzed using computer software. Differences in these CT quantitative parameters between the patients with CTD-ILD and those with CTD without ILD were compared using Mann-Whitney U tests. Furthermore, univariable and multivariable logistic regression analyses were used to establish nomograms to identify the independent predictors associated with the presence of ILD in patients with CTD. The calibration curve evaluates the predictive accuracy, while the decision curve analysis (DCA) evaluates clinical applicability.

RESULTS: The forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), diffusing capacity of the lungs for carbon monoxide corrected for alveolar volume (DLCO/VA) and diffusing capacity of the lungs for carbon monoxide (DLCO) of the CTD with ILD group were significantly lower than those of the CTD without ILD group (all P<0.05). CTD with ILD group had higher percentages of high-attenuation area on inspiratory and expiratory CT (HAA%-IN and HAA%-EXP) (both P<0.05), and lower percentage of low-attenuation area on expiratory CT (LAA%-EXP), functional air trapping (fAT) volume, functional small airway disease (fSAD) volume and fSAD volume ratio (all P<0.001). Additionally, pulmonary vascular parameters including No. vessels, No. vessels cross-sectional area (CSA) <5 mm2 at 6, 12 and 24 mm depth from the pleural surface, BV1, BV5, BV10 and total blood volume (TBV) were significantly decreased in CTD-ILD patients (all P<0.001). Multivariate Ridge regression identified age, sex, DLCO%, FEV1%, EXP HAA%, fSAD ratio, and No. vessels_12mm as independent diagnostic predictors associated with the presence of ILD (all P<0.05). The combined diagnostic model achieved an area under the curve (AUC) of 0.963 [95% confidence interval (CI): 0.920-0.998], with an accuracy of 0.893, sensitivity of 0.941 and specificity of 0.818. The calibration curve demonstrated high consistency between predicted probabilities and actual outcomes.

CONCLUSIONS: QCT can serve as a crucial and highly promising imaging biomarker for the diagnosis and assessment of CTD-ILD.