FDG-PET and MRI in the Evolution of New-Onset Refractory Status Epilepticus

Abstract

Background and purpose: New-onset refractory status epilepticus is a clinical condition characterized by acute and prolonged pharmacoresistant seizures without a pre-existing relevant neurologic disorder, prior epilepsy, or clear structural, toxic, or metabolic cause. New-onset refractory status epilepticus is often associated with antineuronal antibodies and may respond to early immunosuppressive therapy, reflecting an inflammatory element of the condition. FDG-PET is a useful diagnostic tool in inflammatory and noninflammatory encephalitis. We report here FDG-PET findings in new-onset refractory status epilepticus and their correlation to disease activity, other imaging findings, and outcomes.

Materials and methods: Twelve patients who met the criteria for new-onset refractory status epilepticus and who had FDG-PET and MR imaging scans and electroencephalography at a single academic medical center between 2008 and 2017 were retrospectively identified. Images were independently reviewed by 2 radiologists specialized in nuclear imaging. Clinical characteristics and outcome measures were collected through chart review.

Results: Twelve patients underwent 21 FDG-PET scans and 50 MR imaging scans. Nine (75%) patients were positive for autoantibodies. All patients had identifiable abnormalities on the initial FDG-PET in the form of hypermetabolism (83%) and/or hypometabolism (42%). Eight (67%) had medial temporal involvement. All patients (n = 3) with N-methyl-D-aspartic acid receptor antibodies had profound bilateral occipital hypometabolism. Initial MR imaging findings were normal in 6 (50%) patients. Most patients had some degree of persistent hyper- (73%) or hypometabolism (45%) after immunosuppressive therapy. FDG-PET hypometabolism was predictive of poor outcome (mRS 4-6) at hospital discharge (P = .028).

Conclusions: Both FDG-PET hypometabolism and hypermetabolism are seen in the setting of new-onset refractory status epilepticus and may represent markers of disease activity.

Fig 1.

Brain MR imaging, FDG-PET, and EEG findings for P2, a 63-year-old man with glutamic acid decarboxylase 65 encephalitis and normal brain MR imaging findings at the onset of seizures. A, Axial T2-weighted FLAIR image at day 12 of status epilepticus shows bilateral hippocampus and insula T2-weighted hyperintense lesions. B, Axial FDG-PET image at day 12 of status epilepticus shows bilateral hippocampus, amygdala, and insula hypermetabolism. C, Axial T2-weighted FLAIR image at day 49 of status epilepticus shows resolution of hippocampal and insula T2-weighted hyperintense lesions with diffuse atrophy. D, EEG shows left frontotemporal seizures (onset at black arrow) with bilateral periodic discharges before seizure. E, EEG shows bilateral independent periodic discharges (black asterisks).

Fig 2.

Brain MR imaging and FDG-PET findings for P5, a 22-year-old man with NMDA-R antibody encephalitis. A, Axial T2-weighted FLAIR image 7 days before the onset of status epilepticus with normal findings. B, Axial T2-weighted FLAIR image 2 days before the onset of status epilepticus with normal findings. C, Axial T2-weighted FLAIR image at day 28 of status epilepticus shows mild diffuse atrophy. D, Axial T2-weighted FLAIR image at day 63 of status epilepticus shows moderate diffuse atrophy. E, Axial FDG-PET image at day zero of status epilepticus shows marked bilateral occipital-greater than-parietal hypometabolism. F, Axial FDG-PET image at day 12 of status epilepticus shows bilateral inferolateral frontal hypermetabolism with diffuse hypometabolism. G, Axial FDG-PET image at day 56 of status epilepticus shows resolution of bilateral inferolateral frontal hypermetabolism with diffuse cortical hypometabolism. H, Axial FDG-PET image at day 88 of status epilepticus shows moderate bilateral occipital-greater than-parietal hypometabolism. I, Axial FDG-PET image at day 234 following status epilepticus shows mild bilateral occipital hypometabolism.

Fig 3.

Timeline of brain MR imaging, FDG-PET, and the first immunotherapy treatment during initial hospitalization. Not depicted are FDG-PET 2 of P10 at 1397 days and MR imaging 3 of P8 at 415 days.