Brain 18F-fluorodeoxyglucose positron emission tomography: An efficient tool at the initial diagnosis of nonlesional late onset epilepsy.

Abstract

Objective: This study evaluates the diagnostic performance and prognostic value of brain ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) at the initial diagnosis of patients with nonlesional late onset epilepsy (NLLOE).

Methods: In this cohort study at the University Hospital of Nancy, France, newly diagnosed NLLOE patients, >50 years old, were consecutively included from June 2017 to January 2021 and systematically underwent brain ¹⁸F-FDG PET. They were categorized into four presumed etiological NLLOE subtypes: neurodegenerative subtype (NDS; patients with a diagnosis of neurodegenerative disease), microvascular subtype (MVS; patients with ≥3 cardiovascular risk factors and ≥2 vascular lesions on magnetic resonance imaging), inflammatory subtype (IFS; patients meeting international criteria for encephalitis), and unlabeled subtype (ULS). A systematic patient follow-up (at least 2 years) allowed assessment of cognitive outcomes under antiseizure medication by comparing for each patient the proportion of preserved/altered scores between initial and second neuropsychological assessment. Brain ¹⁸F-FDG PET was analyzed using a combined visual and semiquantitative approach at the individual level.

Results: Eighty-seven patients were included (NDS, n = 18; MVS, n = 22; IFS, n = 7; ULS, n = 40). A normal ¹⁸F-FDG PET was observed in 46% of patients, with the final diagnosis of 88% of these patients excluding a neurodegenerative or inflammatory disorder. ¹⁸F-FDG PET had a negative predictive value of 94% for a cognitive decline at follow-up, similar for the overall population (n = 71) and the ULS population (n = 32). Moreover, a PET hypometabolic pattern suggestive of a neurodegenerative disorder was indicative of cognitive decline at follow-up in 74% of cases.

Significance: ¹⁸F-FDG PET as part of the initial diagnosis of NLLOE patients may have a significant impact on both NLLOE diagnosis and cognitive prognosis. For almost half of NLLOE patients, a normal ¹⁸F-FDG PET could help to exclude neurodegenerative and inflammatory epilepsy etiologies as well as future cognitive decline.