All the viruses which cause meningitis may also give raise for encephalitis. More specific types of viral encephalitis occur in epidemic, e.g. Japanese ‘B’ encephalitis, also influenza and herpes simplex viruses are fairly frequently implicated.

Pathology:

The distribution and extent of lesions vary to some extent with the type  of infecting virus. Generally, diffuse damage to cells in the cortex, basal ganglia and brain stem; infiltration between neurons and in the perivascular spaces by polymorphonuclear cells initially & later by lymphocytes and mononuclear cells. There is accompanying neuroglia proliferation.

Clinical Features:

Acute onset, headache, a – ; disturbance of Consciousness (varying from mild drowsiness and coma). Epilepsy of focal or generalized type is common. Foci signs e.g. hemiplegia or tetraplegia, cranial nerve palsies, sensory disturbances may be present,

Diagnosis:

Firstly it should be distinguished from other intracranial diseases, e.g. cerebral tumour or abscess, encephalopathies, encephalomyelitis etc. Investigations are more helpful in excluding other lesions than in confirming the diagnosis of viral encephalitis. C.S.F. pressure and protein content are raised, with lymphocytic pleocytosis. The sugar content is normal. E,E.G. is usually altered. There is a diffuse slowing of the rhythms but the findings are nonspecific except in subacute sclerosing panencephalitis. Serological tests and culture may identify the infecting virus (but the results of such tests are usually available to late to guide treatment).

Treatment

The management of most cases of viral encephalitis consists of nursing care and the prevention of intercurrent infections, Symptomatic treatment,

Prognosis:

This is highly variable; most patients survive and may recover completely but persisting focal defects are frequent.