To analyze quantitative lung densitometry and clinical baseline data of individuals with idiopathic inflammatory myopathy (IIM) and identify risk factors capable of predicting the progression of interstitial lung disease (ILD).

A total of 126 ILD patients were retrospectively enrolled. Baseline CT-derived indices, including Total Lung Volume(TLV, cm3) , Normal Lung Density (NLD, -950 HU to -700 HU), High Attenuation Areas (HAA; -700 HU to -250 HU), Mean Lung Attenuation (MLA) and Normal Lung Index (NLI=NLD/TLV) were measured on chest CT. Clinical baseline data including demographics data, and laboratory parameters were collected. Quantitative lung densitometry and clinical baseline data between ILD progression and non-progression patients were compared. Univariate and multivariate Cox regression analyses were employed to pinpoint effective risk factors for predicting ILD progression in IIM patients.

During 5-year follow-up, 37 of 126 IIM patients (29.37%) suffered ILD progression. HAA, NLI, TLV, MLA, age, CRP, ESR, Ferritin, CEA, PO2, Anti-Ro52, Anti-MDA5, Anti-EJ and Anti-TIFγ were significantly different between ILD progression and non-ILD progression patients (P<0.05). The findings from the Cox univariate regression analysis indicated that elevated CEA levels (HR=1.036, 95% CI 1.004-1.069, P=0.027) and HAA(HR=5.007, 95% CI 1.773-14.144, P=0.002) were connected to an elevated risk of ILD progression in patients with IIM, while PO2 (HR=0.980, 95% CI 0.962-0.997) was a protective factor for ILD progression in patients with IIM (P=0.025), Anti-EJ positivity (HR=0.399, 95% CI 0.175-0.912), Anti-Ro52 positivity(HR=0.437, 95% CI 0.199-0.960) and HR=0.239, 95% CI 0.122-0.468) were risk factors for ILD progression in patients with IIM (P=0.029, 0.039 and 0.001, respectively). Furthermore, the results of Cox multivariate regression analysis reveal that HAA(HR=4.758, 95% CI 1.009-22.440) and Anti-MDA5 positivity(HR=0.127, 95% CI 0.041-0.396) were autonomous prognostic risk factors for ILD progression in individuals with IIM (P=0.002 and 0.001, respectively). When combined HAA (>465.745 cm3) and Anti-MDA5 positivity for diagnosing ILD progression in IIM patients, the ROC curve analysis yielded an AUC of 0.845, which was higher than that of either Anti-MDA5 positivity or HAA  alone(AUC=0.536 and 0.660, respectively).

Among IIM patients, those who are Anti-MDA5-positive, and exhibit HAA (＞465.745cm3) are more likely to experience ILD progression. Baseline HAA has the potential as a prognostic indicator in ILD patients.