From the Guidelines
An EEG in a patient with HSV-1 encephalitis can show characteristic periodic lateralizing epileptiform discharges (PLEDs) in the temporal regions, which are helpful in suggesting a specific etiologic diagnosis of encephalitis. The results of an EEG are generally nonspecific but can be helpful in diagnosing encephalitis, particularly in the early stages of the disease 1. In patients with herpes simplex encephalitis, EEG typically demonstrates a temporal focus with periodic lateralizing epileptiform discharges, which are stereotypical sharp and slow wave complexes occurring at intervals of 2–3 s, typically seen on days 2-14 after symptom onset 1. Some key EEG findings in HSV-1 encephalitis include:
- Periodic lateralized epileptiform discharges (PLEDs) in the temporal regions
- Focal slowing and decreased amplitude in the affected temporal region
- Diffuse slowing of background activity, indicating widespread cerebral dysfunction
- Seizure activity, even if not clinically apparent, as subclinical seizures occur in many HSV encephalitis patients These EEG findings are crucial for early diagnosis and management of HSV-1 encephalitis, as they can appear before changes on MRI become evident 1. It is essential to interpret EEG findings alongside clinical presentation and other diagnostic tests like CSF analysis and MRI to confirm the diagnosis of HSV-1 encephalitis 1.
From the Research
EEG Findings in HSV-1 Encephalitis
The results from an Electroencephalogram (EEG) in a patient with Herpes Simplex Virus type 1 (HSV-1) Encephalitis can show:
- Periodic discharges, which can be lateralized to one side of the brain 2, 3, 4
- Focal seizures or status epilepticus, which can shift in predominance over time 3
- Generalized findings, indicating spread of the disease 3
- Right lateralized periodic discharges, which can be associated with right mesial temporal lobe diffusion restriction on MRI 2
Diagnostic Approach
The diagnostic approach for HSV-1 Encephalitis involves:
- Clinical manifestations, such as fever, weakness, and altered level of consciousness 5, 2, 4
- Imaging studies, such as MRI, which can show temporal lobe abnormalities 2, 4, 6
- Cerebrospinal fluid (CSF) analysis, which can detect HSV-1 DNA by polymerase chain reaction (PCR) 5, 2, 4
- Electroencephalogram (EEG), which can show abnormal findings, such as periodic discharges and seizures 2, 3, 4
Importance of Clinical Suspicion
It is essential to consider the clinical suspicion of HSV-1 Encephalitis, even if the CSF PCR is negative, as false negatives can occur 2, 4. Empiric treatment with acyclovir should be considered in cases with high clinical suspicion, while investigations for alternate treatable diagnoses are continued 2, 4. Continuous EEG can be used to monitor the progression of the disease and prompt escalation in therapy 3.