From the Guidelines
In patients with Herpes Simplex Virus type 1 (HSV-1) Encephalitis, EEG results can show abnormal electrical activity in the brain, particularly temporal focus demonstrating periodic lateralizing epileptiform discharges, which are stereotypical sharp and slow wave complexes occurring at intervals of 2–3 s, as seen in 180% of patients 1. The EEG findings in HSV-1 encephalitis are generally nonspecific but can be helpful in suggesting a specific etiologic diagnosis of encephalitis.
- Key EEG abnormalities include:
- Temporal focus demonstrating periodic lateralizing epileptiform discharges
- Stereotypical sharp and slow wave complexes occurring at intervals of 2–3 s
- Diffuse slow wave activity
- Intermittent rhythmic activity These EEG changes usually occur on days 2-14 after symptom onset 1. The severity of abnormal EEG findings does not usually correlate with the extent of disease in the acute phase of illness, but rapidly improving EEG findings often indicate a good prognosis 1. EEG is also useful in identifying patients with nonconvulsive seizure activity who are confused, obtunded, or comatose 1. It is essential to interpret EEG findings alongside clinical presentation, CSF analysis, and neuroimaging, as EEG findings are not specific to HSV encephalitis alone 1. Serial EEGs may be useful to monitor treatment response, with persistent abnormalities potentially indicating ongoing inflammation or poor prognosis.
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.