Neuroimaging Correlates of Periodic Discharges

Abstract

Despite being first described over 50 years ago, periodic discharges continue to generate controversy as to whether they are always, sometimes, or never "ictal." Investigators and clinicians have proposed adjunctive markers to help clarify this distinction-in particular measures of perfusion and metabolism. Here, we review the growing number of neuroimaging studies using Fluorodeoxyglucose-PET, MRI diffusion, Magnetic resonance perfusion, Single Photon Emission Computed Tomography, and Magnetoencepgalography to gain further insight into the physiology and clinical significance of periodic discharges. To date, however, no definitive consensus exists regarding the features of periodic discharges that warrant treatment intensification. However, an emerging consilience among neuroimaging modalities suggests that periodic discharges can induce a hyperexcitatory state with associated hypermetabolism and hyperperfusion, which may result in local metabolic failure.

FIG. 1.

This is the case of a 74-year-old woman who has a history of right occipital ischemic stroke who presented with new-onset convulsive status epilepticus. Convulsions were aborted with anti-seizure medications. A, Brain MRI with axial FLAIR sequence reveals right occipital encephalomalacia with hyperintensity. B, cEEG at the time of the brain MRI displayed near-continuous right occipital low frequency 0.5 to 0.75 Hz LPDs. C, PET was performed to aid with medication management. It displayed hypometabolism in the right occipital area concordant with the MRI and EEG findings (see arrow). The patient’s mild hypometabolism was speculated to represent possible pseudo-normalization from more what would be expected to be a prominent hypometabolism at baseline. Focal status epilepticus was refractory to treatment including resective surgery and she was discharged with palliative goals. Continuous EEG recording is displayed on a bipolar longitudinal montage at LFF 1 Hz, HFF 70 Hz, Notch on, Timebase 30 mm/second. LFF, low frequency filter; LPDs, lateralized PDs; HFF, high frequency filter.

FIG. 2.

Focal hypermetabolism seen on FDG-PET that is concordant with PDs on cEEG. Case #1 (A–C): A 32-year-old woman with a history of focal epilepsy related to the underlying perinatal stroke presented with clonic movements consistent with epilepsia partialis continua. A, Brain MRI FLAIR axial sequence revealed right frontal lobe postsurgical changes, with FLAIR hyperintense findings seen in the right occipital lobe. B, continuous EEG showed continuous LPDs in addition to a breach artifact and focal anatomic slowing. Epilepsia partialis continua was refractory to medical treatment, and the patient underwent surgical resection that resulted in resolution of the status epilepticus. C, PET reveals concordant hypermetabolism in the right occipital area medially and marked hypometabolism in the right frontal area congruent with her postsurgical resection. Case #2 (D–F): 25-year-old woman presented with convulsive status epilepticus, followed by encephalopathy. D, Initial brain MRI FLAIR axial sequence revealed left parietal right FLAIR hyperintense findings. E, Continuous EEG shows intermittent bursts of low-frequency left temporo-parietal PDs. F, PET reveals concordant hypermetabolism in the left parietal area medially. The patient was treated based on the PET findings with intravenous sedatives, and AED resulted in resolution of LPDs and improvement in mental status back to baseline. FDG-PET, fluorodeoxyglucose-PET; LPDs, lateralized PDs.

FIG. 3.

A 77-year-old man with hypertension presented with encephalopathy. Figures A–C represent the findings before initiation of IV anesthetics. A, Brain MRI FLAIR axial sequences reveal FLAIR hyperintensities in the left posterior quadrant cortical area in addition to periventricular hyperintense white matter changes. B, Continuous EEG displays bursts of high-frequency left posterior quadrant interrupted by generalized voltage attenuations. C, FDG-PET shows hypermetabolism in the right posterior quadrant concordant with the cEEG and MRI findings. Figures D–F represent the phase where the patient was initiated on IV anesthetics. D, MRI FLAIR axial sequences reveal resolution of the hyperintense cortical ribboning in the left posterior quadrant. E, Continuous EEG shows a burst suppression pattern without any periodic discharges. F, FDG-PET shows resolution of the hypermetabolism. Despite treatment with IV anesthetics and anti-seizure medications, the patient did not improve clinically and was thus transitioned to comfort care measures. FDG-PET, fluorodeoxyglucose-PET.