FDG-PET and ASL MRI identify largely overlapping hypermetabolic and hyperperfusion changes in limbic autoimmune encephalitis

Abstract

Background: Arterial spin labeling (ASL) MRI has been anecdotally used to assess brain perfusion in autoimmune encephalitis (AE) and its relationship with [¹⁸F]FDG-PET dysmetabolism has been scarcely investigated.Considering the physiological coupling of metabolism and perfusion, we aimed to evaluate the degree of correspondence between ASL-MRI and [¹⁸F]FDG-PET in AE.

Methods: A retrospective cohort of five patients underwent ASL-MRI and [¹⁸F]FDG-PET during the acute stage and at follow-up. We assessed the presence of regions with hypermetabolism on [¹⁸F]FDG-PET and hyperperfusion on ASL-MRI and evaluated concordance and spatial overlap of these metrics. Clinical assessment scale in AE and modified Rankin Scale were obtained at baseline and follow-up.

Results: In two patients [¹⁸F]FDG-PET and ASL-MRI were unremarkable; in three patients there were anatomically overlapping areas of hypermetabolism and hyperperfusion (average DICE similarity coefficient 0.358). Following immunotherapy, metabolic and perfusion changes consistently demonstrated a progressive normalization, aligning with clinical improvement.

Conclusions: We identified suboptimal anatomical correspondence of abnormalities assessed with [¹⁸F]FDG-PET and ASL-MRI. Hyperperfusion and hypermetabolism might reflect differently AE-related pathophysiological correlates, but they both demonstrate ability to monitor disease activity. ASL-MRI is a promising marker of disease activity in AE and a favorable alternative to [¹⁸F]FDG-PET due to its cost-effectiveness, safety, and wide availability.