Marked Reversibility of Functional Small Airway Disease Following Reduction of Hazardous Inhalational Exposure: A <scp>PRM CT</scp> Case Report

We report a case illustrating the role of parametric response mapping (PRM) in detecting and monitoring small airway disease (SAD) related to occupational inhalational exposure. A 52-year-old woman, a lifelong never-smoker with chronic occupational exposure to metal cutting-fluid fumes and metal particles, presented with exertional dyspnea and moderate airflow obstruction. PRM CT revealed PRM-functional small airway disease (PRM-fSAD) of 15.7% and PRM-emphysema of 0.2%. After 1.5 years of increased unprotected exposure, PRM-fSAD rose to 46.2%, with stable spirometry but reduced diffusing capacity and more frequent exacerbations. Following workload reduction and consistent mask use, PRM-fSAD decreased to 2.8% accompanied by symptomatic and functional improvement. This case supports PRM as a reliable imaging biomarker for early detection of exposure-related SAD, even before spirometric decline, and highlights the potential reversibility of occupational lung injury with timely intervention.