Inflammatory response in lungs and extrapulmonary sites detected by [${}^{18}$F] fluorodeoxyglucose PET/CT in convalescing COVID-19 patients tested negative for coronavirus

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has resulted in an ongoing global pandemic of coronavirus disease 2019 (COVID-19). The challenges associated with imaging infected patients have resulted, to date, in a paucity of metabolic imaging studies of patients with severe COVID-19 infection. Furthermore, it remains unclear if any abnormal metabolic events are taking place in patients who have recovered from COVID-19. To use [${}^{18}$F] fluorodeoxyglucose ([${}^{18}$F] FDG) positron emission tomography/computed tomography (PET/CT) to measure metabolic activity in inflamed organs of patients convalescing post severe COVID-19 infection. A prospective study was performed in seven convalescing patients who were recovering from severe COVID-19 infection in February 2020. Prior to [${}^{18}$F] FDG PET/CT, all patients had received two consecutive negative results of real-time reverse transcriptase polymerase chain reaction (RT-PCR) for SARS-CoV-2 nucleic acid. Clinical intake including symptoms, treatment, laboratory test results, and follow-up was performed. The PET/CT images of COVID-19 patients were compared to a control group of patients that were matched for age and sex. Residual pulmonary lesions were present in all patients and maximum standard uptake value (SUVmax), average standard uptake value (SUVavg), maximum CT intensity (CTmax), and average CT intensity (CTavg) were all significantly greater than in the control group (p < 0.01 for all). In addition, SUVmax and SUVavg were significantly greater in the mediastinal lymph node and liver, and SUVmax was significantly greater in the spleen, of COVID-19 patients compared with controls (p < 0.05 for all). For the spleen, SUVmax (r${}^2$ = 0.863, p = 0.003) and SUVavg (r${}^2$ = 0.797, p = 0.007) were significantly correlated with blood lymphocyte count, and which was below the normal range in five of the seven (71.4%) patients convalescing post severe COVID-19 infection. [${}^{18}$F] FDG PET/CT quantitative analysis has shown that significant inflammation remained in lungs, mediastinal lymph nodes, spleen, and liver after two consecutive negative RT-PCR tests in patients convalescing post severe COVID-19 infection.