Focal hypermetabolism in suspected non-convulsive status epilepticus

To evaluate ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) as a biomarker in suspected non-convulsive status epilepticus (NCSE) by characterizing electroclinical-metabolic correlations and quantifying focal hypermetabolism.

We included adult patients with rhythmic and periodic patterns (RPPs) undergoing ¹⁸F-FDG PET for suspected NCSE. Two neurologists reviewed patient electroencephalography (EEG) recordings (0-30 min post-injection) using 2021 American Clinical Neurophysiology Society (ACNS) criteria. ¹⁸F-FDG PET images were blindly assessed by two nuclear medicine specialists for the presence and lobar location of focal hypermetabolism. Structural magnetic resonance imaging (MRI) studies enabled PET co-registration and segmentation. Patients with available MRI scans were compared to external age/sex-matched and in-house validation healthy control datasets. We calculated intra-subject standardized uptake value (SUV) z-scores within the gray matter and then compared this approach to SUV ratio (SUVR) methods (using either the cerebellum or the pons as reference region) using consensus visual assessment as the reference standard. For hypermetabolic volume quantification, we chose the lowest threshold with 100% specificity (z ≥ 3.0) to eliminate false-positive volumes, which yielded 62% sensitivity. Resulting volumes were correlated with lateralized periodic discharge (LPD) main modifiers (frequency, prevalence, evolution, plus-factors).

Of 24 adult patients (median age 62 years, 15 female), 17 (71%) had LPDs. Qualitatively, focal hypermetabolism was present in 92% of patients (n = 22), with strong concordance between visual PET findings and EEG lateralization in patients with LPDs. Twenty-three patients underwent MRI and were compared to external age/sex-matched (n = 23) and in-house validation (n = 22) healthy control datasets. Our technique outperformed traditional SUVR methods (AUC = 0.92 vs 0.55-0.64, p < .001) in detecting focal hypermetabolism. In patients with LPDs, hypermetabolic volumes ranged from 0 to 21.4 mL, with substantial volumes (>10 mL) observed across all discharge frequencies.

¹⁸F-FDG-PET revealed focal hypermetabolism in most suspected NCSE cases, including in cases with equivocal EEG patterns. In patients with LPDs, the extent of focal hypermetabolism was highly variable across different frequencies.