Neurological Disorders: Herpes Encephalitis

The term encephalitis indicates inflammation of the brain tissue, and herpes encephalitis (HSE) is caused by a virus named herpes simplex (HSV) or sometimes just herpes virus.

Few other viruses that are included in the herpes family include;

• Chickenpox virus (Varicella Zoster)
• EB virus (causes infectious mononucleosis) etc.

HSV is of two types; type 1 & 2, HSE is mostly caused by type 1. Herpes simplex type 2 mostly causes the genital infection in adults although the neonatal herpes encephalitis too is caused by this virus subtype. This is acquired by the baby during delivery through the herpes infected vagina. In adults, herpes simplex type 2 may occasionally cause meningitis. A Neurologist is frequently involved in the care of all these patients.

This encephalitis is seen throughout the world. It is considered as a sporadic disease in the sense it is seen randomly rather than endemics (cases occurring in the same place for a long time) or in epidemics (several cases occurring in the same place simultaneously). No race, sex, or age is exempt, although incidence is more in younger and older people.

The herpes viruses are notorious to live in a dormant state for a long time in the body after the primary or initial infection, and they do so usually in the nerve ganglions (a cluster of neurons or nerve cells). It is hypothesized that such hibernating viruses in a ganglion by name trigeminal ganglion (ganglion on trigeminal or fifth cranial nerve) become reactive for some reason and then travel towards the brain along the nerve fiber (axon) and ultimately reach the brain tissue and infiltrate the neurons. Another cranial nerve by name olfactory nerve (nerve of smell or first cranial nerve) may also be implicated with the virus-entry to the brain.

The following symptoms are frequently seen including;

• Severe headache
• Fever
• Nausea & vomiting
• Altered sensorium (disorientation/Confusion)
• Decreased level of consciousness
• Obtundation/Coma
• Fits (seizures) etc.

The following tests are arranged when this condition is suspected;

• CSF (cerebrospinal fluid) analysis
• Brain CT or Brain MRI scan
• EEG

CSF shows findings suggestive of encephalitis like increased mononuclear cells & protein; usually normal glucose; and negative gram stain/ bacterial antigens/culture etc.

PCR for herpes antigen is confirmatory most of the times.

CT or MRI generally show temporal and/or frontal lobe inflammatory changes, swelling, hemorrhagic areas etc.

EEG may show a characteristic finding called a PLED (periodic lateralized epileptiform discharges).

Patients are invariably admitted to the hospital. Specific treatment is Acyclovir infusion at 10 mg/kg three times per day x about 14 days. Supportive & symptomatic treatments are given. If seizures are present anti seizure medications are given.