Reevaluating the relevance of 18F-FDG PET findings for diagnosis of neurosarcoidosis: a case series.

Objective: The diagnosis of neurosarcoidosis (NS) remains challenging due to the difficulty to obtain central nervous system (CNS) biopsies. Various diagnostic parameters are considered for the definition of possible, probable and definite NS. Magnetic resonance imaging (MRI) is the imaging gold standard and considered in diagnostic criteria. Fluorodeoxyglucose positron emission (¹⁸F-FDG PET) is sometimes performed additionally to identify possible systemic biopsy targets. However, at present, its findings are not incorporated into the diagnostic criteria for neurosarcoidosis (NS).

Methods: We conducted a single center retrospective search for the period 2020-2022, for patients with neurological symptoms in a diagnostic context of suspected NS who underwent MRI and additional ¹⁸F-FDG PET scans to identify potential hypermetabolism in the CNS and biopsy targets.

Results: We identified three cases of NS, where Gadolinium-enhanced MRI scans did not show abnormalities while ¹⁸F-FDG PET revealed hypermetabolic lesions in areas of the CNS. Additional MRI scans were still inconclusive for structural changes. We diagnosed a "probable" NS in all cases with histopathological confirmation of systemic sarcoidosis which led to an intensified therapy regime.

Discussion: ¹⁸F-FDG PET is an early indicator for metabolic changes. It appears to be a useful add-on to improve accuracy of diagnostic criteria in suspected NS without MRI findings.