ABSTRACT
Background-Aim: Cognitive impairment may represent a long lasting symptom after COVID-19 resolution and FDG brain PET is useful to evaluate if brain metabolic changes are transient or long lasting. Hypometabolism was shown in many brain areas, i.e. cingulate cortex, bilateral gyrus rectus, prefrontal and orbitofrontal cortex and cerebellar vermis. Methods: We report the case of a 62 years old man with type 2 diabetes, affected by COVID-19 infection in October 2020. After resolution, the patient had short-term memory loss and speech deficit affecting daily living and working activities and referred to the Gerontology and Geriatrics Institute (Univ. of Perugia). Neurological examination and neuropsychological tests were carried out and no alterations were found. In October 2021, the neurological examination was still normal, as well as neuropsychological tests. Brain MRI showed only two small chronic ischemic foci without bi-hemispheric white matter clinically significant abnormalities. In November 2021, the patient underwent FDG brain PET/CT (discovery ST, G.E.) according to standard protocols and images were evaluated both qualitatively and semiquantitatively. Results: An area of moderate significant hypometabolism was identified in the precuneus (predominant on the right side) and others multiple small and mild hypometabolic regions were localized in bilateral pre-frontal cortex, sensorimotor and parietal cortex both on left hemisphere. PET and MRI fusion images (Syngo.via VB10B image processing software, Siemens) showed that hypometabolic areas corresponded to structurally intact parenchyma at MRI. In January 2022 clinical and neuropsychological follow up did not evidence cognitive impairment, although the patient still felt depressed and impaired in memory, attention and daily living activities. Conclusions: In this case, FDG brain PET/CT was the only diagnostic procedure showing findings consistent with patient symptoms. In particular, precuneus hypometabolism may represent in this patient an early hallmark of dementia (i.e. Alzheimer's disease-AD), although other characteristic brain areas are not significantly impaired (i.e. cingulate cortex). In this case, FDG brain PET use, during follow up, could be crucial to evaluate if the metabolic changes may evolve into a chronic state, thus supporting mild cognitive impairment clinical suspect due to AD or confirming a stable COVID related neuronal damage. Furthermore, a second normal FDG brain PET/CT scan may suggest a post-acute infection transient phase, preluding to normal functional status. In conclusion, FDG brain PET/CT may represent an important diagnostic tool in modifying subsequent diagnostic assessment suggesting or routinely clinical follow up or other investigations for dementia (i.e. amyloid PET, amyloid and Tau protein liquor measurement). In our study, fused PET and MRI images were used, although hybrid PET/MRI system could be the choice option if available.