Encephalitis is an acute inflammation of the brain, commonly caused by a viral infection. Sometimes, encephalitis can result from a bacterial infection, such as bacterial meningitis, or it may be a complication of other infectious diseases like rabies (viral) or syphilis (bacterial). Certain parasitic protozoal infestations, like by toxoplasma, can also cause encephalitis in people with compromised immune systems. Brain damage occurs as the inflamed brain pushes against the skull, and, depending on its severity, can lead to death.
Features
Patients with encephalitis suffer from fever, headache, vomiting, confusion, drowsiness and photophobia. The patients could also suffer from weakness, seizure, and less commonly, stiffness of the neck. Rarely, the patients may have limb stiffness, slowness in movement and clumsiness, depending on the specific part of the brain involved. The symptoms of encephalitis are caused by the brain's defense mechanisms activating to get rid of the infection, including swelling, small bleedings and cell death.
Aetiology
Victims are usually exposed to viruses resulting in encephalitis by insect bites or food and drink. The most frequently encountered agents are arboviruses (carried by mosquitoes or ticks, see also tick-borne meningoencephalitis) and enteroviruses (coxsackievirus, poliovirus and echovirus). Some of the less frequent agents are measles, rabies, mumps, varicella and herpes simplex viruses. Incidentally type 3 Lyssavirus (Mokola virus), found in Australia, causes a lethal encephalitis which hardly resembles rabies. Numerically, the most important cause of encephalitis worldwide is probably Japanese encephalitis, as it causes up to 50 000 cases a year, with about 15 000 deaths. Japanese encephalitis affects East and Southeast China, Korea, Japan, Taiwan, Southeast Asia, Papua New Guinea, South Asia and even Northern Australia. The most widespread cause of encephalitis worldwide, however, is Herpes Simplex encephalitis. The herpes simplex virus causes inflammation on the temporal lobe of the brain, and if not treated, half to three quarters of the patients succumb. In very young children, however, the virus could affect any part of the brain, even sparing the temporal lobe.
An interesting cause of viral encephalitis is the Nipah virus. It was first discovered in September 1994 in northern Australia when 13 horses and their owner died.
Diagnosis
Neurologic examination usually reveals a stiff neck due to the irritation of the meninges covering the brain. Examination of the cerebrospinal fluid obtained by a lumbar puncture procedure reveals increased amounts of proteins and white blood cells with normal glucose. A CT scan examination is performed to reveal possible complications of brain swelling, brain abscess or bleeding. Lumbar puncture procedure is performed only after the possibility of prominent brain swelling is excluded by a CT scan examination.
Treatment
Treatment is usually symptomatic. Reliably tested specific antiviral agents are available only for a few viral agents (e.g. aciclovir for herpes encephalitis) and are used with limited success. In patients who are very sick, supportive treatment, such as mechanical ventilation, is equally important.
Encephalitis lethargica
Encephalitis lethargica is an atypical form of encephalitis which caused an epidemic from 1917 to 1928. There have only been a small number of isolated cases since, though in recent years a few patients have shown very similar symptoms. The cause is now thought to be a bacterial agent. As depicted in the book Awakenings by doctor Oliver Sacks, which was made into the film starring Robin Williams and Robert De Niro, the disease sometimes caused catatonia which could persist for decades.
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