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]
Synonyms and keywords: HSE; Herpes viral encephalitis; Herpes meningoencephalitis
Overview
Herpes simplex encephalitis is a severe viral infection of the central nervous system. Herpes simplex encephalitis may be classified according to origin of disease into 2 subtypes: oral (HSV-1) and genital (HSV-2). The exact pathogenesis of herpes simplex encephalitis is not fully understood.[1] Herpes simplex encephalitis must be differentiated from other diseases that cause fever, headache, and altered mental status. Physical examination findings for herpes simplex encephalitis are generally unspecific. Herpes simplex encephalitis constitutes a medical emergency. If left untreated, approximately 70% patients with herpes simplex encephalitis progress to mortality.[2] Common complications of herpes simplex encephalitis include meningitis, increased intracranial pressure, and coma. Laboratory findings consistent with the diagnosis of herpes simplex encephalitis include increased leukocytes in cerebrospinal fluid.[3] Polymerase chain reaction is critical in the diagnosis of herpes simplex encephalitis, as there is a 95-98% specificity and sensitivity beginning as early as 1 day after symptoms first appear and lasting up to 1 week after treatment.[1] Magnetic resonance imaging is the imaging modality of choice for herpes simplex encephalitis. The mainstay of therapy for herpes simplex encephalitis includes antiviral therapy. The drug of choice is acyclovir.[4]
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.[5]
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:[6][7]
| Disease | Findings |
|---|---|
| Encephalopathy | Presents with steady depression, generalized seizures. Generally there is absence of 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; Complications include 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.[2][6] Approximately 2000 cases of herpes simplex encephalitis occur within the United States annually.[4] Approximately 90% of cases are caused by HSV-1, with 10% caused by HSV-2. HSV-2 is most often observed among immunocompromised individuals and neonates.
Age
Approximately 50% of individuals that develop herpes simplex encephalitis are over 50 years of age.[3]
Gender
There is no gender predilection to the development of herpes simplex encephalitis.[4]
Race
There is no racial predilection to the development of herpes simplex encephalitis.[4]
Season
Unlike other cases of encephalitis, there is no seasonal predilection to the development of herpes simplex encephalitis.[4]
Risk Factors
The most potent risk factor in the development of herpes simplex encephalitis is immune deficiency. Other risk factors include age and human contact.[4][8]
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
- 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 damage is present. Only 2.5% of survivors regain full brain function.[3]
Diagnosis
Diagnostic Criteria
The diagnosis of herpes simplex encephalitis is based on the IDSA criteria, which can be found here.[9]
History and Symptoms
If possible, a detailed and thorough history from the patient is necessary. Symptoms of herpes simplex encephalitis include:[4]
- Decreased alertness
- Confusion
- Fever
- Headache
- Drowsiness
- Lethargy
- Inability to produce or comprehend language
- Difficulty swallowing
- Seizures
Physical Examination
Physical examination findings for herpes simplex encephalitis are generally unspecific. Common physical examination findings of herpes simplex encephalitis include:
- Fever
- Confusion
- Aphasia
- Coma
- Chorioretinitis
- Conjunctivitis
- Erythema multiforme
- Genital and/or oral ulcers
Laboratory Findings
Laboratory findings consistent with the diagnosis of herpes simplex encephalitis include increased leukocytes in cerebrospinal fluid obtained via lumbar puncture.[3] Polymerase chain reaction is critical in the diagnosis of herpes simplex encephalitis, as there is a 95-98% specificity and sensitivity beginning as early as 1 day after symptoms first appear and lasting up to 1 week after treatment.[1]
CT
Computed tomography may be helpful in the diagnosis of herpes simplex encephalitis. Findings on CT suggestive of herpes simplex encephalitis include subtle low density within the anterior and medial temporal lobe and the insular cortex.[10][11] Subtleties become more apparent over time and may progress to hemorrhage, and may eventually spread to the other temporal lobe after 7-10 days.[3]
MRI
Magnetic resonance imaging is the imaging modality of choice for herpes simplex encephalitis. Findings on MRI suggestive of herpes simplex encephalitis include:[10][12]
- T1
- General edema in the affected region
- Hyperintense signal if complicated by subacute hemorrhage
- T1 C+ (Gd)
- Early, enhancement is generally absent
- Later, enhancement is variable and may appear as:
- Gyral enhancement
- Leptomeningeal enhancement
- Ring enhancement
- Diffuse enhancement
- T2
- Hyperintensity of affected white matter and cerebral cortex
- DWI/ADC
- GE/SWI
- May demonstrate blooming if hemorrhagic
The following video demonstrates herpes simplex encephalitis on MRI:
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Treatment
Medical Therapy
The mainstay of therapy for herpes simplex encephalitis includes antiviral therapy. The drug of choice is acyclovir.[4] Supportive therapy for herpes simplex encephalitis includes breathing assistance, intravenous fluids, anti-inflammatory drugs, and anticonvulsant medication.[13]
Primary Prevention
Effective measures for the primary prevention of herpes simplex encephalitis include abstinence from sexual contact, remain in a long-term mutually monogamous relationship with an uninfected partner, use of latex condoms, and conversing with possible sexual partners regarding infections. Vaccines against herpes simplex have been developed but remain experimental.
References
- ↑ 1.0 1.1 1.2 1.3 Schlossberg D. Clinical Infectious Disease. Cambridge University Press; 2008.
- ↑ 2.0 2.1 2.2 2.3 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.
- ↑ 3.0 3.1 3.2 3.3 3.4 Whitley RJ, Gnann JW (2002). "Viral encephalitis: familiar infections and emerging pathogens". Lancet. 359 (9305): 507–13. PMID 11853816.
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 M.D. JE, Dolin R, Blaser MJ. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, Expert Consult Premium Edition. Saunders; 2014.
- ↑ Dinn J (1980). "Transolfactory spread of virus in herpes simplex encephalitis". Br Med J. 281 (6252): 1392. PMID 7437807.
- ↑ 6.0 6.1 Kennedy PG (2004). "Viral encephalitis: causes, differential diagnosis, and management". J Neurol Neurosurg Psychiatry. 75 Suppl 1: i10–5. PMC 1765650. PMID 14978145.
- ↑ Davis LE (2000). "Diagnosis and treatment of acute encephalitis". The Neurologist. 6 (3).
- ↑ 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
- ↑ The Management of Encephalitis: Clinical Practice Guidelines by the Infectious Diseases Society of America. http://www.idsociety.org/uploadedFiles/IDSA/Guidelines-Patient_Care/PDF_Library/Encephalitis.pdf Accessed on February 16, 2016.
- ↑ 10.0 10.1 Herpes simplex encephalitis. Radiopaedia.org (2016). http://radiopaedia.org/articles/herpes-simplex-encephalitis Accessed on February 9, 2016.
- ↑ Zimmerman RD, Russell EJ, Leeds NE, Kaufman D (1980). "CT in the early diagnosis of herpes simplex encephalitis". AJR Am J Roentgenol. 134 (1): 61–6. doi:10.2214/ajr.134.1.61. PMID 6766039.
- ↑ Bulakbasi N, Kocaoglu M (2008). "Central nervous system infections of herpesvirus family". Neuroimaging Clin N Am. 18 (1): 53–84, viii. doi:10.1016/j.nic.2007.12.001. PMID 18319155.
- ↑ Encephalitis: Treatment and drugs. Mayo Clinic. http://www.mayoclinic.org/diseases-conditions/encephalitis/basics/treatment/con-20021917 Accessed on February 11, 2016