COVID-19 pneumonia: relationship between inflammation assessed by whole-body FDG PET/CT and short-term clinical outcome

Abstract

Purpose: [18F]-2-Fluoro-2-deoxy-D-glucose PET/CT (FDG PET/CT) is a sensitive and quantitative technic for detecting inflammatory process. Glucose uptake is correlated with an increased anaerobic glycolysis seen in activated inflammatory cells such as monocytes, lymphocytes, and granulocytes. The aim of the study was to assess the inflammatory status at the presumed peak of the inflammatory phase in non-critically ill patients requiring admission for COVID-19.

Methods: Patients admitted with COVID-19 were prospectively enrolled. FDG PET/CT was performed from day 6 to day 14 of the onset of symptoms. Depending on FDG PET/CT findings, patients' profiles were classified as "inflammatory" or "low inflammatory." FDG PET/CT data were compared with chest CT evolution and short-term clinical outcome. All inflammatory sites were reported to screen potential extra-pulmonary tropism.

Results: Thirteen patients were included. Maximum standardized uptake values ranged from 4.7 to 16.3 in lungs. All patients demonstrated increased mediastinal lymph nodes glucose uptake. Three patients (23%) presented mild nasopharyngeal, two patients (15%) bone marrow, and five patients (38%) splenic mild increase in glucose uptake. No patient had significant digestive focal or segmental glucose uptake. There was no significant physiological myocardial glucose uptake in all patients except one. There was no correlation between PET lung inflammatory status and chest CT evolution or short-term clinical outcome.

Conclusion: Inflammatory process at the presumed peak of the inflammatory phase in COVID-19 patients is obvious in FDG PET/CT scans. Glucose uptake is heterogeneous and typically focused on lungs.

Trial registration: NCT04441489. Registered 22 June 2020 (retrospectively registered).

Keywords: COVID-19; FDG PET/CT; Inflammation.

Fig. 1

Study flow chart. Twenty-six patients with laboratory-confirmed COVID-19 were hospitalized at the Centre Hospitalier Princesse Grace of Monaco from March 27th to May 3rd, 2020. Twelve patients were excluded because they were admitted out of the selected time period from the onset of the symptoms or without chest CT ground-glass opacities or consolidation. One patient was secondary excluded because further elicitation retrospectively revealed the onset of symptoms occurred 22 days before FDG PET/CT study

Fig. 2

A 53-year-old man patient with moderate respiratory symptoms referred for FDG PET/CT at day 14 after the onset of symptoms. Images showed multiple peripheral and bilateral ground-glass opacities with intense increased FDG uptake (SUV_max 16.3). The following day, respiratory status dramatically improved without need of supplemental oxygen, and patient was discharged from hospital 3 days later. Left: A CT transverse slice, B FDG PET slice, and C FDG PET and CT-fused images. Right: whole-body maximal intensity projection (MIP) image, displaying also mediastinal lymph nodes FDG uptake

Fig. 3

A 55-year-old man patient who presented severe respiratory symptoms in the days before FDG PET/CT. Images showed bilateral consolidation with mild increased FDG uptake (SUV_max 5). Despite this mild inflammation, the patient remained symptomatic for days requiring oxygen therapy through nasal canula at low flow rates and was discharged from hospital only 13 days later. Left: A CT transverse slice, B FDG PET slice, and C FDG PET and CT-fused images. Right: whole-body MIP image demonstrating that FDG uptake in mediastinal lymph nodes is above lung FDG uptake (respectively, SUV_max 6.9 versus 5)