Visual interpretation of brain hypometabolism related to neurological long COVID: a French multicentric experience

BACKGROUND: This multicentre study aimed to provide a qualitative and consensual description of brain hypometabolism observed through the visual analysis of (18)F-FDG PET images of patients with suspected neurological long COVID, regarding the previously reported long-COVID hypometabolic pattern involving hypometabolism in the olfactory bulbs and other limbic/paralimbic regions, as well as in the brainstem and cerebellum. METHODS: From the beginning of August 2021 to the end of October 2021, the brain (18)F-FDG PET scans of patients referred for suspected neurological long COVID with positive reverse transcription polymerase chain reaction (RT-PCR) and/or serology tests for SARS-CoV-2 infection were retrospectively reviewed in three French nuclear medicine departments (143 patients; 47.4 years old ± 13.6; 98 women). Experienced nuclear physicians from each department classified brain (18)F-FDG PET scans according to the same visual interpretation analysis as being normal, mildly to moderately (or incompletely) affected, or otherwise severely affected within the previously reported long-COVID hypometabolic pattern. RESULTS: On the 143 brain (18)F-FDG PET scans performed during this 3-month period, 53% of the scans were visually interpreted as normal, 21% as mildly to moderately or incompletely affected, and 26% as severely affected according to the COVID hypometabolic pattern. On average, PET scans were performed at 10.9 months from symptom onset (± 4.8). Importantly, this specific hypometabolic pattern was similarly identified in the three nuclear medicine departments. Typical illustrative examples are provided to help nuclear physicians interpret long-COVID profiles. CONCLUSION: The proposed PET metabolic pattern is easily identified upon visual interpretation in clinical routine for approximately one half of patients with suspected neurological long COVID, requiring special consideration for frontobasal paramedian regions, the brainstem and the cerebellum, and certainly further adapted follow-up and medical care, while the second half of patients have normal brain PET metabolism on average 10.9 months from symptom onset.