Acute viral encephalitis is an acute inflammation of the nervous system where brain, brain stem or cerebellum is involved due to a virus; It may be primary or post infectious. Primary form occurs when there is direct invasion or replication of virus in the nervous system while post infectious follows either other viral infections or after administration of certain vaccines. The involvement of meninges and other parts of nervous system when inflammation spreads to spinal cord is termed encephalomyelitis.
A number of viruses can cause clinical picture of acute viral encephalitis and these viruses range from Arboviruses (Japanese, ST Louis, Westren Equine, Kyasanur forest disease (KFD). Rhabdovirus (Rabies) Entero viruses (Cox sackie, ECHO), Herpes virus (VZV, EB virus, CMV). Influenza para influenza, viruses to other like measles, rubella, mumps etc.
In most of the cases of acute viral encephalitis there is prodromal period lasting for a few days and symptoms range from headache, myalgia, body aches, malaise and features of upper respiratory tract infection. Mild fever is often present. The above symptoms lasting for a few days are followed by neurologic symptoms which come acutely and abruptly.
There is headache, photo phobia, vomiting and alterations in state of consciousness. Signs of meningeal irritation appear followed by convulsions, confusion, disorientation, stupor and even coma. Focal neurological deficits are found depending on the site of involvement.
These defects range from hemiparesis, sensory defects, aphasia, ocular palsies and ataxia.
Brain stem involvement can effect the respiratory center and other vital centers.
Investigations of acute viral encephalitis
Blood counts are within normal limits. CSF is usually under normal or slightly elevated pressure. It may be clear or slightly turbid. Protein content is slightly elevated with normal glucose content. There is rise in cell count ranging from 50 to 500 per micro liter.
Viral isolation from blood and CSF is generally not possible. Serological tests may help in identifying the causative organism if there is four fold increase in antibody titers. EEG shows a slow wave activity with disruption of normal rhythm with high amplitude bursts and spike and wave complexes.
CT and MRI may show changes in the form of generalized or localized foci of infection.
It is based on clinical picture of acute onset of illness which generally comes in epidemics and involves large number of people. Course of the disease is variable that is it may have a short lived benign course or a severe fulminating course leaving behind a number of sequlae.
The treatment for acute viral encephalitis is mainly supportive. Steroids are employed empirically though their benefit is doubtful. If a patient is having convulsion then anti-convulsants (Phenytoin 100mg three times a day) are given. Cerebral edema is relieved by marmitol (20% solution in 20 minutes every 6 hly), Furesmide and steroids.
Cases where Herpes simplex virus encephalitis is suspected, antiviral therapy (acyclovir) may be employed with good results.
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