Encephalitis and myelitis are diffuse
inflammatory processes leading to neuronal death and brain swelling
Diffuse inflammation of the brain (encephalitis)} and cord (myelitis) is caused
by viral, rickettsial and certain bacterial organisms (mainly Listeria,
Treponema, and Borrelia).
The main viral organisms responsible for this pattern
of infection are herpes simplex, polio and rabies. Clinically, diffuse
inflammation causes neurological dysfunction manifest by myelopathy (motor and
sensory signs) or encephalopathy (confusion and reduced level of consciousness).
Macroscopically, there is hyperaemia of the meninges, petechial haemorrhages in
the brain, and brain swelling due to oedema. In some types, e.g. encephalitis
due to Herpes simplex, there is extensive brain necrosis. The results of
encephalitis or myelitis are death of neurons, cuffing of cerebral blood vessels
by lymphoid cells, and astrocytic gliosis.
Depending on the cause, viral cellular inclusion bodies may be seen. For
example, cytoplasmic Negri bodies are seen in rabies, and nuclear viral
inclusion bodies are seen in herpes encephalitis. |
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