Quantitative spectral computed tomography biomarkers for idiopathic inflammatory myopathy-associated interstitial lung disease: a dual-layer detector computed tomography study.

BACKGROUND

High-resolution computed tomography (HRCT) is recommended for early diagnosis and monitoring in idiopathic inflammatory myopathy (IIM)-associated interstitial lung disease (ILD). Multiparameter spectral computed tomography (CT) has demonstrated the potential to assess lung disease. However, the application of quantitative spectral CT biomarkers in IIM-associated ILD remains underexplored. This study aimed to investigate the performance of quantitative spectral CT biomarkers in characterizing and differentiating between patients with antisynthetase syndrome (ASS)-associated ILD and those with polymyositis/dermatomyositis (PM/DM)-associated ILD.

METHODS

This retrospective study enrolled 164 patients treated with ASS or PM/DM who underwent noncontrast dual-layer spectral CT (DLCT) between March 2024 and September 2024. After 15 cases were excluded (age <18 years, n=3; malignancy, n=2; nonclinical ILD, n=10), 68 patients with ASS-associated ILD and 81 with PM/DM-associated ILD were analyzed. Quantitative parameters including lung lobe volume, monoenergetic CT number (MCTN) at 70 keV, effective atomic number (Zeff), and electron density (ED) of each lung lobe were compared between the two groups. The distribution of ILD pattern was also compared.

RESULTS

The ILD pattern distribution did not differ significantly between the two groups. Meanwhile, in the analysis of spectral CT parameters, patients with ASS, as compared to the those with PM/DM, demonstrated significantly reduced lung volume [right lower lobe (RLL): 455.72±232.00 vs. 589.85±225.66 cm3, P<0.001; left lower lobe (LLL): 418.33±214.43 vs. 535.92±203.30 cm3, P<0.001], a higher MCTN (RLL: -708.80 vs. -743.10 HU, P=0.042; LLL: -705.10 vs. -745.40 HU, P=0.008), and higher ED [RLL: 29.65 vs. 26.10 percentage of electron density relative to water (%EDW), P=0.041; LLL: 2 9.80 vs. 26.00 %EDW, P=0.008]. In the subgroup analysis of nonspecific interstitial pneumonia (NSIP)-dominant cases, these differences persisted for the left lower-lobe (ED: 27.70 vs. 24.35 %EDW, P=0.033).

CONCLUSIONS

Patients with ASS-associated ILD, as compared to those with PM/DM-associated ILD, had reduced volume, enhanced MCTN, and greater ED of the lower lung lobes. The difference in disease severity between these patient groups could be detected by spectral CT parameters.