Visual interpretation of brain hypometabolism related to neurological long COVID: a French multicentric experience, 2022, Verger et al

Abstract

Background
This multicentre study aimed to provide a qualitative and consensual description of brain hypometabolism observed through the visual analysis of 18F-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 18F-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 18F-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 18F-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.

Open access, https://link.springer.com/article/10.1007/s00259-022-05753-5

 

They evaluated four brain regions on the PET, looking in axial, coronal and sagittal planes. Standard technique, using 18F labelled glucose (18FDG).

• fronto-orbital olfactory regions
• other limbic/paralimbic regions
• brainstem
• cerebellum

The colour map they've used is "French" (mais bien sûr): red > yellow > green > blue. When looking for abnormalities the idea is to look for areas of reduced avidity, corresponding to lower labelled-glucose uptake and use. Typically symmetry/asymmetry is helpful, but these studies are looking at relatively symmetric change, so experience in interpretation counts. Their examples look compelling and reproducible, as long as the colour thresholds are uniform as the paper describes.

Here is their coronal view of three patients, highlighting the fronto-olfactory region, which would presumably relate to the common symptom of loss of sense of smell. Left image is normal, middle is mild-moderate, right is severe.

Looking at the part of the brain above the nose, arrowed on the right image. Normal shows a continuous band of high uptake (in red); moderate shows a reduced amount of red with central reduction (yellow); severe shows a central defect which is at background levels of brain uptake (green).



Ignore the dots of colour below the brain, they represent activity in the extra-ocular muscles and optic nerves - some people are just more "twitchy" with their eyes. The middle patient shows this the most.

 

See also —
Similar patterns of [ 18 F]-FDG brain PET hypometabolism in paediatric and adult patients with long COVID: a paediatric case series (2022, Morand et al)

I've added arrows for the two children with follow-up, showing improved brainstem uptake.