Herpes simplex encephalitis
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Anthony Gallo, B.S. [3]
Overview
Herpes simplex encephalitis is a severe viral infections of the central nervous system.
Classification
Herpes simplex encephalitis may be classified according to origin of disease into 2 subtypes: oral (HSV-1) and genital (HSV-2).
Pathophysiology
The exact pathogenesis of herpes simplex encephalitis is not fully understood.[1] It is thought that herpes simplex encephalitis is caused by the retrograde transmission of virus from a peripheral site on the face to the brain along a nerve axon following HSV-1 reactivation.[2] The virus lies dormant in the ganglion of the trigeminal or fifth cranial nerve but the exact pathogenesis remains unknown. The olfactory nerve may also be involved in herpes simplex encephalitis.[3]
Causes
Herpes simplex encephalitis may be caused by either HSV-1 or HSV-2.
Differentiating Herpes simplex encephalitis from Other Diseases
Herpes simplex encephalitis must be differentiated from other diseases that cause fever, headache, and altered mental status, such as:[4][5]
| Disease | Findings |
|---|---|
| Encephalopathy | Presents with steady depression, generalized seizures. Generally absent are fever, headache, leukocytosis, and pleocytosis. MRI often appears normal. |
| Meningitis | Presents with inflammation of the meninges, which may develop in the setting of an infection, physical injury, cancer, or certain drugs; it may have an indolent evolution, resolving on its own, or may present as an rapidly evolving inflammation, causing neurologic damage and possible mortality. |
| Other Viral encephalitis | Presents with acute inflammation of the brain, caused by a viral infection; it may complicate into severe brain damage as the inflamed brain pushes against the skull, potentially leading to mortality. |
| Bacterial encephalitis | Presents with acute inflammation of the brain, caused by a bacterial infection; it may complicate into severe brain damage as the inflamed brain pushes against the skull, potentially leading to mortality. |
| Brain abscess | Presents with an abscess in the brain caused by the inflammation and accumulation of infected material from local or remote infectious areas of the body; the infectious agent may also be introduced as a result of head trauma or neurological procedures. |
| Acute disseminated encephalomyelitis | Presents with scattered foci of demyelination and perivenular inflammation; it can cause focal neurological signs and decreased ability to focus. |
Epidemiology and Demographics
Incidence
The incidence of herpes simplex encephalitis is approximately 0.1-0.2 per 100,000 individuals worldwide.[4][2] Approximately 2000 cases of herpes simplex encephalitis occur within the United States annually.[6] Approximately 90% of cases are caused by HSV-1, with 10% caused by HSV-2. HSV-2 is most often observed among immnuocompromised individuals and neonates.
Age
Approximately 50% of individuals that develop herpes simplex encephalitis are over 50 years of age.[7]
Gender
There is no gender predilection to the development of herpes simplex encephalitis.[6]
Race
There is no racial predilection to the development of herpes simplex encephalitis.[6]
Season
Unlike other cases of encephalitis, there is no seasonal predilection to the development of herpes simplex encephalitis.[6]
Risk Factors
The most potent risk factor in the development of herpes simplex encephalitis is weakened immune system. Other risk factors include age and human contact.[8][6]
Natural History, Complications and Prognosis
Natural History
Herpes simplex encephalitis constitutes a medical emergency. If left untreated, approximately 70% patients with herpes simplex encephalitis progress to mortality.[2]
Complications
Common complications of herpes simplex encephalitis include:[8]
- Meningitis
- Increased intracranial pressure
- Cranial nerve palsy
- Shock
- Coma
- Seizures
- Aspiration pneumonia
- Respiratory failure
Prognosis
Prognosis for herpes simplex encephalitis is generally poor. Even with rapid treatment, it is fatal in approximately 20% of cases. In approximately 50% of surviving patients, long-term neurological damange is present. Only 2.5% of survivors regain full brain function.[7]
Diagnosis
History and Symptoms
Most individuals with HSE show a decrease in their level of consciousness and an altered mental state presenting as confusion and changes in personality. Some patients with HSE will have seizures.
Physical Examination
Laboratory Findings
Increased numbers of white blood cells can be found in their cerebrospinal fluid without the presence of pathogenic bacteria and fungi, and they typically have a fever.[2]
MRI
CT
CT or MRI scans changes as the disease progresses, first showing abnormalities in one temporal lobe of the brain, which spread to the other temporal lobe 7–10 days later.[2]
Other Diagnostic Studies
The electrical activity of the brain (detected using EEG changes as the disease progresses, first showing abnormalities in one temporal lobe of the brain, which spread to the other temporal lobe 7–10 days later.[2]
Treatment
Medical Therapy
Surgery
Primary Prevention
Secondary Prevention
References=
- ↑ Schlossberg D. Clinical Infectious Disease. Cambridge University Press; 2008.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Whitley RJ (2006). "Herpes simplex encephalitis: adolescents and adults". Antiviral Res. 71 (2–3): 141–8. doi:10.1016/j.antiviral.2006.04.002. PMID 16675036.
- ↑ Dinn J (1980). "Transolfactory spread of virus in herpes simplex encephalitis". Br Med J. 281 (6252): 1392. PMID 7437807.
- ↑ 4.0 4.1 Kennedy PG (2004). "Viral encephalitis: causes, differential diagnosis, and management". J Neurol Neurosurg Psychiatry. 75 Suppl 1: i10–5. PMC 1765650. PMID 14978145.
- ↑ {{cite journal| author=Davis LE| title= Diagnosis and treatment of acute encephalitis. | journal= The Neurologist | year= 2000 | volume= 6 | issue= 3|
- ↑ 6.0 6.1 6.2 6.3 6.4 M.D. JE, Dolin R, Blaser MJ. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, Expert Consult Premium Edition. Saunders; 2014.
- ↑ 7.0 7.1 Whitley RJ, Gnann JW (2002). "Viral encephalitis: familiar infections and emerging pathogens". Lancet. 359 (9305): 507–13. PMID 11853816.
- ↑ 8.0 8.1 Meningitis and Encephalitis Fact Sheet. National Institute of Neurological Disorders and Stroke. National Institutes of Health (2015). http://www.ninds.nih.gov/disorders/encephalitis_meningitis/detail_encephalitis_meningitis.htm Accessed on February 9, 2015