Quantitative 18F-FDG PET-CT can assess presence and extent of interstitial lung disease in early severe diffuse cutaneous systemic sclerosis.

Background: This study aimed to assess the quantitative uptake of ¹⁸F-FDG PET-CT in the lungs of patients with early severe diffuse cutaneous systemic sclerosis (SSc) with and without interstitial lung disease (ILD), compared to controls. In patients with SSc-ILD, ¹⁸F-FDG uptake was correlated to high-resolution computed tomography (HRCT) and pulmonary function test (PFT) parameters. Methods: A prospective, cross-sectional study was conducted, involving 15 patients with SSc-ILD, 5 patients with SSc without ILD, and 7 controls without SSc. ¹⁸F-FDG PET-CT scans were performed following standardized protocols, and quantitative analysis of tracer uptake was conducted in predefined lung regions. In addition, HRCT scans were evaluated for ILD-related radiologic abnormalities. Between-group differences were compared with non-parametric tests, while correlations with PFT parameters were analyzed using Spearman correlation coefficients. Results: ¹⁸F-FDG uptake was mainly increased in the dorsobasal lung fields of patients with SSc-ILD compared to SSc without ILD and controls (p = 0.03 and p < 0.001, respectively). ¹⁸F-FDG uptake was higher in SSc patients with extensive ILD (≥ 20% vs < 20%, p = 0.04) and correlated with lower DLCO% (R = -0.59, p = 0.02). Ground-glass opacities, with or without reticulation, corresponded to increased ¹⁸F-FDG uptake. Conclusions: ¹⁸F-FDG PET-CT can detect metabolic activity in the lungs of patients with early severe diffuse cutaneous SSc and ILD, correlating with higher ILD extent (≥ 20%) and lower DLCO%. These results suggest the potential utility of ¹⁸F-FDG PET-CT in the early detection of ILD (progression) and aiding in risk stratification.