Interobserver Variability and Histopathologic Correlation of Lung Ultrasonography in a Bleomycin-Induced Mouse Model of Systemic Sclerosis

Objectives: Interstitial lung disease (ILD) is a major cause of morbidity and mortality in patients with systemic sclerosis (SSc). This study aimed to evaluate interobserver variability and the relationship between lung ultrasonography (LUS) findings and histological fibrosis severity in a bleomycin (BLM)-induced mouse model of SSc. Materials and Methods: Twenty female BALB/c mice were randomly assigned to a control group (n = 10) or a BLM-treated group (n = 10). Pulmonary fibrosis was induced by daily subcutaneous administration of BLM for three weeks. Two blinded observers (a radiologist and a rheumatologist) performed LUS using a high-frequency linear probe and calculated scores based on B-line distribution. Lung fibrosis was evaluated by Masson’s trichrome staining and quantified using the Ashcroft scoring system. Interobserver agreement was assessed with Cohen’s kappa, and correlations were analyzed using Spearman’s rank test. Results: Control mice exhibited normal lung architecture, whereas all BLM-treated mice developed moderate to severe fibrosis, with significantly higher Ashcroft scores. LUS revealed multiple B-lines, pleural irregularities, and loss of A-lines in BLM-treated mice. LUS scores were considerably higher in the BLM group (p < 0.001). Radiologist-assessed scores showed a strong correlation with Ashcroft scores (ρ = 0.78), while rheumatologist-assessed scores demonstrated a moderate correlation (ρ ≈ 0.62). Interobserver agreement was moderate, with discrepancies mainly in intermediate fibrosis stages. Conclusions: LUS is a useful non-invasive method for semiquantitative assessment of pulmonary fibrosis in this SSc model. Its correlation with histological severity supports clinical relevance, while moderate interobserver variability highlights the need for standardized protocols and training.