Re: Neurological Manifestations as marker of H1N1 virulence?
eMedicine Specialties > Neurology > Neurological Infections
Viral Encephalitis
Updated: Jan 11, 2007
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The annual incidence of viral encephalitis is most likely underestimated, especially in developing countries, because of problems with pathogen detection. Japanese B encephalitis affects at least 50,000 individuals per year.
In a recent study from Finland, the incidence of viral encephalitis in adults was 1.4 cases per 100,000 persons per year. HSV was identified most often as the cause (16%), followed by varicella-zoster (5%), mumps (4%), and
influenza A viruses (4%).
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History
* Viral encephalitis is marked by acute onset of a febrile illness.
* Patients with viral encephalitis generally experience signs and symptoms of leptomeningeal irritation (eg, headache, fever, neck stiffness).
* Patients with viral encephalitis also develop focal neurological signs; seizures; and alteration of consciousness, starting with lethargy and progressing to confusion, stupor, and coma.
* Behavioral and speech disturbances are common.
* Abnormal movements can be seen but are rare.
* Involvement of the hypothalamic/pituitary axis can lead to hyperthermia or poikilothermia.
* Specific clues taken from the patient's history depend on the viral etiology. Clinical findings reflect disease progression according to viral tropism for different CNS cell types. Particular clinical manifestations of different encephalitides can be reviewed in Tables 2-4. Some important clinical presentations are as follows:
o Atypical presentations include a reversible frontal lobe and limbic syndrome without disturbances of consciousness or motor function. These presentations have been described in children with influenza virus infection.
o HSV-1 encephalitis and HSV-2 encephalitis have subacute forms, presenting with psychiatric syndrome and anterior opercular syndrome, known as benign recurrent meningitis. HSV-1 encephalitis may produce a brainstem encephalitis, and HSV-2 encephalitis may produce a myelitis.
o West Nile virus infection is usually asymptomatic in areas of endemic disease. In symptomatic individuals, an influenzalike illness occurs after incubation of 3-15 days; CNS involvement occurs in fewer than 15% of cases. Severe neurological infection is more common when the virus is introduced in an area of nonendemic disease. In 1999, during the New York City outbreak, 62 patients developed encephalitis, and 7 died (a case fatality rate of 12%, with all deaths occurring in older patients). Axonal neuropathy, demyelinating polyneuropathy similar to that in Guillain-Barr? syndrome, encephalitis with and without muscle weakness, and aseptic meningitis were described.
o Japanese B encephalitis typically affects children and young adults. Older adults are affected in epidemics. The clinical presentation includes a nonspecific prodrome and frequent seizures.
o Dengue fever classically presents with a severe influenzalike illness or dengue hemorrhagic fever. Less commonly, dengue fever can lead to encephalitis or encephalopathy, transverse myelitis, and mononeuropathy or polyneuropathy similar to that in Guillain-Barr? syndrome. The hemorrhagic form may also cause hepatic failure leading to a Reye syndrome?like illness.
o Enteroviral encephalitis is usually associated with a good prognosis. However, enterovirus 71 has a high mortality rate and can present with herpangina or enteroviral hand, foot, and mouth disease. Complications include myocarditis and acute flaccid paralysis. Enterovirus 71 can cause a chronic meningoencephalitis in patients who are immunocompromised.
o Mumps encephalitis typically starts 3-10 days after parotitis and usually resolves without sequelae, except for occasional hydrocephalus due to ependymal cell involvement. Measles does not usually cause acute encephalitis.
o Rabies usually incubates 20-60 days but is capable of incubating for years. Infection does not occur in all humans bitten by an infected animal but is uniformly fatal when clinical disease develops. After a prodrome of fever, headache, malaise, seizures, and behavioral abnormalities, hydrophobia and aerophobia supervene. Coma and death occur in one to several weeks. Once symptoms start, treatment is ineffective.
o Recently in southern Vietnam,
a viral encephalitis caused by avian influenza A (H5N1) and not involving the respiratory tract was diagnosed in 2 siblings: a 4-year-old boy, who presented with severe diarrhea, seizures, coma, and death and his sister. His CSF only revealed high protein, but H5N1 was isolated from CSF, fecal, throat, and serum specimens.
