The inflammation of brain tissue caused by virus, bacteria, fungi and parasites; parenchymal infection of the brain is termed as encephalitis.
Encephalitis is classified according to the cause
- Bacterial Encephalitis: bacterial infection of the brain substances is usually secondary to the involvement of the meninges rather than a primary bacterial parenchymal infection that progresses to form brain abscesses. However, tuberculosis and neurosyphilis are two primary bacterial involvements of the brain parenchyma. Brain abscesses may arise by one of the following routes:
- By dueit implantation of organisms e.g. Following compound fractures of the skull, intracranial surgery etc.
- By local extension of infection e.g. chronic suppurative otitis media, mastoiditis and sinusitis
- By haemotogenous spread e.g. from primary infection in heart such as acute bacterial endocarditis and from lungs such as in bronchiectasis
Clinically, there is usually evidence of reactivation of infection at the primary site preceding the onset of cerebral symptoms. The features of abscess are a fever, headache, vomiting, seizure and facial neurological deficits depending upon the location of the abscess. Brain abscess is most common in cerebral hemispheres and less frequent in the cerebellum and basal ganglia.
Tuberculoma is an intracranial mass occurring secondary to the dissemination of tuberculosis elsewhere in the body. Tuberculomas may be solitary or multiple.
Syphilitic lesions of the CNS used to be common and serious, but more recently there is evidence of atypical neurosyphilis in cases of HIV/AIDS. The lesions in syphilis may be a form of syphilitic meningitis found in secondary syphilis and neurosyphilis consisting of tabes dorsalis and generalized paralysis of the insane occurring in tertiary stage.
- Syphilitic meningitis:
This is a form of chronic meningitis characterized by distinctive perivascular inflammatory reaction of plasma cells and endarteritis obliterans.
- Tabes dorsalis(locomotor ataxia)
There is slowly progressive degeneration of the posterior roots of the spinal nerve and the posterior columns of the spinal cord by the spirochaetes. These changes produce loss of coordination of muscle and joints resulting in the locomotor ataxia.
- General paralysis of the insane
This is the results of diffuse, parenchymal involvement by the spirochaetes with widespread lesions in the Nervous system. The symptoms consist of a motor, sensory and psychiatric abnormalities.
- Viral encephalitis
A member of viruses can infect the Central Nervous System and produce either aseptic either meningitis or viral encephalitis but sometimes a combination of both termed meningoencephalitis is present. Most viral infection of the Central Nervous System is end result of proceeding infection in the other tissues and organs, usually, a preceding phase of extraneural viral replication before the involvement of Nervous system occurs.
Most of the viruses reach the Nervous System via bloodstream before which they enter the body of various routes e.g.
- Infection of skin and mucous membrane (in herpes simplex and herpes zoster-varicella)
- By alimentary tract (in enteroviruses including poliovirus)
- By arthropod bite (in arbovirus)
- Transplacental infection (in cytomegalovirus)
- Through body fluids in AIDS (in HIV infection)
- Rabies Virus
- Fungal and Protozoal Encephalitis
Mycotic disease of the Central Nervous System develops by bloodstream from systemic deep mycoses elsewhere in the body. They are particularly more common in immunosuppressed individuals such as AIDS, a patient with lymphomas and other cancer.
Some fungi which may disseminate to Central Nervous System are candida Albicans, Mucor, Aspergillus fumigatus, cryptococcus neofromans, Histoplasma copsulatum and Blastomyces dermatitis. Besides fungal infections, CNS may be involved in protozoal diseases such as involved in protozoal diseases such as malaria, toxoplasmosis, amoebiasis, trypanosomiasis and cysticercosis.
It can be developed as a result of a direct infection to the brain by a virus, bacterium, or fungus, or when the immune system responds to a previous infection; the immune system mistakenly attacks brain tissue.
It can split into three main categories of viruses:
- Common viruses: including HSV (herpes simplex virus) and EBV (Epstein-Barr Virus)
- Childhood viruses: measles and mumps
- Arboviruses (spread by mosquitoes, ticks and other insects)- Japanese encephalitis, tick-borne encephalitis
Secondary (post-infection) encephalitis
- caused by a complication of a viral infection
- Symptoms start to appear days or even weeks after the initial infection and the patient’s immune system treats healthy brain cells as foreign organisms and attacks them
It usually affects children, older adults, individuals with weak immune systems and people living in the mosquito-prone areas.
Sign/ symptoms of Encephalitis
The onset is sudden with
- High fever
- A headache
- Neck rigidity
- Change in level of consciousness
- Difficulty in speech
As the condition of patient deteriotes, s/he no longer responds to the environment and goes into a coma.
Diagnosis is based on the observation of symptoms and course of illness. An elevated lymphocytic WBC count is noted in the CSF, protein level elevated and the glucose level is normal. Following investigations are also done:
- A neurological examination is generally used to find that the patient is confused and drowsy
- CT – Scan may be useful in detecting the changes in the structure of the brain, also to rule out other causes, such as stroke, a tumour or an aneurysm
- A lumbar puncture, where a sample of cerebrospinal fluid from the spine is drawn which might reveal the higher-than-normal levels of protein and white blood cells
- An EEG (electroencephalograph) is done that helps to monitor the electrical activity of the brain may show the sharp waves in one or both of the temporal loves in patients with encephalitis
Treatment is symptomatic since no effective drug is known as encephalitis. The treatment of the encephalitis focuses on the alleviating symptoms. Supportive and symptomatic treatment is carried in such as:
- Steroids, to combat cerebral oedema
- Osmotic diuretic to reduce intracranial pressure
- Tracheostomy if respiratory difficulties occur
- Phenytoin- anticonvulsant for convulsion
- Sedative for restlessness
- Aspirin to relieve a headache
- Loss of memory: herpes simplex virus encephalitis affected patient
- Behavioral or personality changes: anxiety, frustration, mood swings, anger
- Language and speech problems
Death occurs within 12-24 hours of onset of symptoms due to clouding of the meninges and degeneration of brain cells. Mortality ranges from 5-60%
Prevention of Encephalitis
- Vaccines: proper vaccination and keeping up-to-date with vaccines is the most effective way of reducing the risk of developing encephalitis-like measles, mumps and rubella vaccine
- Use of mosquito sprays, appropriate clothing, avoiding mosquito-infested areas helps the chance of being bitten.
- Adequate treatment of infection such as sinusitis, mastoiditis, and ear infection
- Use strict aseptic technique during all intracranial operations
- Use strict aseptic technique in changing dressing
- Vaccination for endemic reasons