A quantitative study: investigating the diagnostic value of using dual-layer spectral computed tomography in differentiating idiopathic inflammatory myopathy-associated interstitial lung disease

Abstract

Interstitial lung disease (ILD) is the primary clinical manifestation of antisynthetase syndrome (ASS) and polymyositis/dermatomyositis (PM/DM), and disease progression leads to poor outcomes. To facilitate early differential diagnosis, this study evaluated the value of quantitative spectral computed tomography (CT) parameters in differentiating ASS-ILD from PM/DM-ILD. This retrospective study included 69 patients with ASS-ILD patients and 96 patients with PM/DM-ILD patients who underwent spectral CT and high-resolution computed tomography (HRCT) scans. Quantitative parameters, including lung lobe volume, 70 keV monoenergetic CT number (MCTN), effective atomic number (Zeff), and electron density (ED), were measured in each lung lobe. Spectral CT parameters were compared between the two groups among patients with the same radiological patterns and features. Bonferroni correction ( p  < 0.00625) was applied to account for multiple testing. Compared with the PM/DM-ILD group, the ASS-ILD group had significantly smaller volumes and higher MCTN and ED values in the right lower lobe (RLL) and left lower lobe (LLL) (all adjusted p  < 0.05). Among patients with the same nonspecific interstitial pneumonia (NSIP) pattern, RLL volume (374.79 [291.08, 619.35] vs. 596.22 ± 193.33 cm 3 , raw p  < 0.001) and LLL volume (364.13 [255.83, 567.04] vs. 563.74 ± 189.98 cm 3 , raw p  < 0.001) were smaller in the ASS-ILD group than in the PM/DM-ILD group. Among patients with ground-glass opacity (GGO), LLL ED (29.7 [24.1, 43.8] vs. 25.3 [20.05, 32.78] %EDW, raw p  = 0.003) and MCTN (-706.3 [-763.15, -562.5] vs. -749.7 [-802.98, -678.33] HU, raw p  = 0.003) were higher in the ASS-ILD group than in the PM/DM-ILD group. Receiver operating characteristic (ROC) analysis indicated that RLL volume had the best performance among the evaluated dual-layer spectral CT parameters for discriminating between ASS-ILD and PM/DM-ILD (AUC = 0.727), with a sensitivity of 79.2% and a specificity of 58%. Dual-layer spectral CT provides complementary quantitative information for differentiating ASS-ILD from PM/DM-ILD even among patients with similar HRCT patterns or signs, especially in the lower lung lobes. It may serve as a useful adjunct to conventional HRCT, clinical assessment, and serological testing.