Assessment of alveolar capillary membrane permeability using technetium 99m-diethylene triamine pentaacetate (Tc99m–DTPA) aerosols in patients with diffuse cutaneous systemic sclerosis – a cross-sectional study

Interstitial lung disease (ILD) in diffuse cutaneous systemic sclerosis (dcSSc) often develops early but remains clinically silent, as dyspnea appears usually after substantial fibrosis. Reduced activity from musculoskeletal limitations further delays recognition. This study assessed alveolar-capillary permeability using 99mTc-DTPA aerosol scintigraphy in dcSSc patients and correlated clearance rates with high-resolution computed tomography (HRCT) and spirometry. In this cross-sectional study at a tertiary center in South India (December 2018–January 2021), patients fulfilling ACR/EULAR 2013 dcSSc criteria underwent 99mTc-DTPA aerosol scintigraphy, HRCT, and spirometry. Among 61 participants, the mean DTPA clearance half-time (T½) was 48.11 ± 23.99 minutes. Patients with ILD had significantly faster clearance than those without ILD (44.06 ± 17.37 vs 63.03 ± 37.28 minutes, <i>p</i> = 0.01). T½ correlated negatively with Warrick’s CT score (<i>r</i> = −0.310, <i>p</i> = 0.015) and positively with FVC (<i>r</i> = 0.287, <i>p</i> = 0.026). ROC analysis showed an AUC of 0.646 (95% CI 0.455–0.837); at a cutoff of 49.62 minutes, sensitivity was 68.6% and specificity 60%. The specificity increased to 80% and 90% for cutoffs of 36.83 and 35.48 minutes, respectively. DTPA clearance was significantly faster in dcSSc patients with ILD. Aerosol scintigraphy may detect early alveolar-capillary dysfunction before radiologic or spirometric changes. Further studies incorporating DLCO and longitudinal follow-up are warranted.