Persistent Lung Inflammation After Clinical Resolution of Community-Acquired Pneumonia as Measured by 18FDG-PET/CT Imaging

Abstract

Survivors of community-acquired pneumonia (CAP) are at increased risk of cardiovascular disease, cognitive and functional decline, and death, but the mechanisms remain unknown. Do CAP survivors have evidence of increased inflammatory activity in their lung parenchyma on 2-deoxy-2-[18F]fluoro-d-glucose (18FDG)-PET/CT imaging after clinical resolution of infection? We obtained 18FDG-PET/CT scans from 22 CAP survivors during their hospitalization with pneumonia (acute CAP) and 30 to 45days after hospital discharge (post-CAP). In each set of scans, we assessed the lungs for foci of increased 18FDG uptake by visual interpretation and by total pulmonary glycolytic activity (tPGA), a background-corrected measure of total metabolic activity (as measured by 18FDG uptake). We also measured, post-CAP, the glycolytic activity of CAP survivor lung areas with volumes similar to the areas in 28 matched historical control subjects without pneumonia. Overall, 68%of CAP survivors (95%CI, 45%-85%) had distinct residual areas of increased 18FDG uptake in their post-CAP studies. tPGA decreased from 821.5 (SD, 1,140.2) in the acute CAP period to 80.0 (SD, 81.4) in the post-CAP period (P= .006). The tPGA post-CAP was significantly higher than that in lung areas of similar volume in control subjects (80.0 [SD, 81.4] vs-19.4 [SD, 5.9]; P< .001). An important proportion of CAP survivors have persistent pulmonary foci of increased inflammatory activity beyond resolution of their infection. As inflammation contributes to cardiovascular disease, cognitive decline, functional waning, and mortality risk in the general population, this finding provides a plausible mechanism for the increased morbidity and mortality that have been observed post-CAP.