Encephalitis and Herpes Simplex Virus (HSV)

SSPE (Subacute Sclerosing Panencephalitis)

Late measles infection where the virus hides in the nerves and reactivates, causing brain inflammation.
EEG pattern: Big, juicy, slow (e.g., one per ten seconds) periodic discharges.
It is treatable, but the brain damage is often irreversible by the time of diagnosis.
Measles is rare in the US due to vaccination, but SSPE can occur in unvaccinated individuals.

Herpes is the most important virus in the field of EEG.
CJD (Creutzfeldt-Jakob Disease) is caused by a misfolded protein (prion), not a virus.
- Normal proteins misfold into a "ball of string" shape, preventing other proteins from folding correctly.
- It is an infectious disease, but not viral.
- CJD is fascinating, but it is not a virus.

Encephalitis: Inflammation of the brain itself (cortex, white matter).
Meningitis: Inflammation of the covering of the brain (dura, arachnoid, pia).
Ventriculitis: Inflammation of the ventricles in the center of the brain.
Encephalitis is often encountered in EEG when patients present with confusion.
It is essential to document encephalitis history due to increased epilepsy risk.

Pork tapeworms (neurocysticercosis) are a major cause of epilepsy worldwide.
- The life cycle involves pigs eating eggs from human feces, and humans then consuming the infected pork.
- Infection occurs when humans ingest the eggs directly, leading to worms invading muscles and the brain.
- This is less common in The US due to meat inspection but prevalent in regions with poor sanitation.

Number one cause of encephalitis worldwide.
Specifically, Herpes Simplex Virus (HSV) types 1 and 2.
HSV-1 (oral herpes): Most people have it; causes cold sores.
HSV-2 (genital herpes): Up to a quarter of adults have been exposed by age 50.
- Most exposed individuals remain asymptomatic.
- Symptomatic individuals develop genital ulcers with high viral loads.
Herpes viruses are neurotropic, meaning they reside in nerves.
They can reactivate due to stress, other infections, or weakened immune systems.

Herpes Simplex Virus types 1 and 2
Varicella-Zoster Virus (VZV): causes chickenpox and shingles (zoster).
- If one gets the vaccine, one is safe from getting VZV/Chickenpox.
- Zoster is a reactivation of the chickenpox virus in a nerve, causing a painful rash in the nerve's distribution.
Cytomegalovirus (CMV): Causes congenital neurological problems in infected fetuses, eye infections, and blindness.
Epstein-Barr Virus (EBV): Causes mononucleosis; linked to multiple sclerosis.
HHV-6, 7, and 8: Seen in immunocompromised patients with seizures.

HSV-1 resides in the geniculate ganglia, a nerve bundle connected to the trigeminal nerve.
The trigeminal nerve innervates the face, mouth, and hairline.
Reactivation causes the virus to travel along the nerve, resulting in cold sores.
Rarely, the virus travels backward along the nerve into the brain through the foramen ovale.
Foramen Ovale: The hole in the skull through which the trigeminal nerve passes.

The foramen ovale is located near the mesial temporal lobe, including the hippocampus.
Damage to the hippocampus is highly associated with epilepsy.
HSV-1 can cause damage and bleeding in this region, leading to seizures.

The foramen ovale is a "window into the brain" because of its proximity to the temporal lobe.
Sphenoidal Electrodes (Don't Use):
- A barbaric technique that involves inserting a needle through the cheek to reach the foramen ovale.
- Risks: Pain, carotid artery puncture, infection.
- No more useful than T1 electrodes.
T1/T2 Electrodes:
- Located in the cheek area, overlying the temporal lobe.
- T1 and T2 are ambiguous colloquial names; the correct names are F9/AF9.
- Subtemporal electrodes are valuable but often omitted due to difficulty in placement.
Foramen Ovale Electrodes (Surgical Implantation):
- An electrode can be surgically implanted through the foramen ovale for direct recording from the temporal lobe.
- Performed under fluoroscopy, avoiding the need for craniotomy.
- Risks include trigeminal nerve damage and thalamic injury.

HSV tracks along the trigeminal nerve, through the foramen ovale, into the brain.
It causes brain cell damage and bleeds, which are likely to cause seizures.
The most common infectious cause of brain damage.
Treatable with early intervention.
Symptoms:
- Mild fever, flu-like symptoms.
- Confusion followed by aphasia.
- Lethargy, coma, and potentially death.
- Progression can occur rapidly over days.

Early EEG: Focal slowing, particularly in the left temporal region.
Progression: Can lead to rhythmic delta activity (RDA) or lateralized periodic discharges (LPDs).
- Rhythmic verses Periodic
- Rhythmic: no gap present.
- Periodic: gap present.
Late Stages: May show continuous spike-wave activity, and left hemisphere flattening.

EEG changes in HSV encephalitis reflect the virus spreading across the brain.
Early diagnosis and treatment are crucial to prevent irreversible brain damage and death.