Rationale: Herpes Simplex Virus (HSV) is a prevalent neurotropic virus that causes necrotizing encephalitis (HSE), complicated by acute seizures and long-term epilepsy. EEG findings of epileptiform discharges are frequent, and their prognostic value has been suggested in previous studies but remains controversial. We aim to discuss the evolution of EEG patterns in HSE and their prognostic implications. Methods: We conducted a single-center, retrospective study that included 34 consecutive patients diagnosed between January 2010 and September 2018. HSV CNS infection was confirmed by both detection of HSV DNA in cerebral spinal fluid (CSF) and presence of clinical signs and imaging findings suggestive of parenchymal involvement. We reviewed EEG findings, seizure burden, outcome at discharge (modified Rankin Scale or mRS), discharge disposition, length of stay, long term seizure burden and .
Results: Acute seizures occurred in 47% of patients (16 out of 34). EEG was recorded in 82% (28 of 34) of patients and the indications were: clinical seizures (13), transient aphasia (5), altered mental status (10). The median delay of EEG from the onset of symptoms was four days (IQR=7.25) and the median duration of recording was four days (IQR=5). EEG seizures were captured in 21% of patients (6/28). All had non-convulsive seizures (NCS) with a focal onset. Other EEG finding included: focal slowing in 72% (20/28), lateralized periodic discharges (LPDs) in 36% (10/28), sharp waves in 29% (8/28), bilateral LPDs in 14% (4/28). Seizures occurred in five of the ten patients with LPDs (50%) and three out of the four with non-exclusive bilateral LPDs (75%). Most seizures occurred within the first 24 hours of recording, required one antiepileptic drug (AEDs, average=1.14, SD=0.38) and lasted less than 24 hours in 80% of the cases. Once controlled, seizures did not recur during the hospital course. The patients were monitored on EEG for a median of five days after seizures stopped (IQR=6.75). The presence of restricted diffusion on MRI, but not contrast enhancement, was associated with the occurrence of seizures (p=0.017). Poor outcome at discharge, defined as a mRS of three or more, was not associated with epileptiform discharges or seizures. The presence of acute seizures was not associated with a longer hospital course or a long-term cognitive decline. Seven patients (21%) developed epilepsy during follow-up, and this was associated with the occurrence of acute seizures during index admission (p=0.0021). Significant cognitive impairment was seen in patients with recurrent seizures after discharge (p=0.0025). Conclusions: HSE seems to have a monophasic epileptic presentation acutely that responds well to AEDs. Seizures and epileptiform discharges in the acute phase of HSE did not predict a poor outcome. Seizure recurrence after hospital discharge was associated with significant cognitive decline. Funding: Please list any funding that was received in support of this abstract.: NONE Click here to view image/table