Cerebral 18F-FDG PET hypometabolism in long COVID

Abstract

An individual profile of glucose hypometabolism has been reported, using 18F-FDG brain PET imaging at resting-state, in long COVID patients with neurological symptoms. These abnormalities describe an encephalic network with a possible olfactory gateway, involving the olfactory gyrus and the regions connected to these structures: the limbic and paralimbic regions, the brainstem and the cerebellum. This hypometabolic profile is similarly found in adults and children, in comparison to healthy subjects, in comparison to patients with psychiatric disorders, and in comparison to patients with a physical deconditioning due to the confinement. The severity of hypometabolism is correlated with the severity of symptoms, their frequency, and the duration of evolution. Brain PET imaging with 18F-FDG could thus objectify the cerebral involvement of long COVID. This examination also provides arguments for differential diagnosis, in particular for neurodegenerative diseases, or possible encephalitis/encephalopathies. Neuroimaging experts from the European Association of Nuclear Medicine (EANM) recently clarified the clinical usefulness of this examination, also listing the pitfalls to avoid, and the next perspectives in terms of clinical and pathophysiological implications for long COVID. A cerebral 18F-FDG PET scan could be considered, after dedicated clinical evaluation, in the event of persistence of symptoms after a post-infectious period of 3 to 6 months, or in the event of worsening, in order to eliminate differential diagnoses, and to carry out the cerebral assessment. These metabolic abnormalities could reflect dysfunction of astrocytes and associated glutamatergic neurotransmission dysregulation, linked to neuro-inflammatory microglial activation.