Herpes simplex encephalitis
| Herpesviral encephalitis|
Herpes simplex Microchapters
Herpes simplex encephalitis On the Web
Synonyms and Keywords: HSE; Herpes viral encephalitis; Herpes meningoencephalitis
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 two subtypes: oral (HSV-1) and genital (HSV-2). The exact pathogenesis of herpes simplex encephalitis is not fully understood. 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. 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. 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 one day after symptoms first appear and lasting up to one week after treatment. 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.
The exact pathogenesis of herpes simplex encephalitis is not fully understood. It is believed that herpes simplex encephalitis is caused by the retrograde transmission of thevirus from a peripheral site on the face to the brain along a nerve axon following HSV-1 reactivation. 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.
Differentiating Herpes simplex encephalitis from Other Diseases
|Meningitis||Classic triad of fever, nuchal rigidity, and altered mental status||Photophobia, phonophobia, rash associated with meningococcemia, concomitant sinusitis or otitis, swelling of the fontanelle in infants (0-6 months)|
|Brain abscess||Fever, headache, hemiparesis||Varies depending on the location of the abscess; clinically, visual disturbance including papilledema, decreased sensation; on imaging, a lesion demonstrates both ring enhancement and central restricted diffusion|
|Demyelinating diseases||Ataxia, lethargy||Multiple sclerosis: clinically, nystagmus, internuclear ophthalmoplegia, Lhermitte's sign; on imaging, well-demarcated ovoid lesions with possible T1 hypointensities (“black holes”)|
|Substance abuse||Tremor, headache, altered mental status||Varies depending on type of substance: prior history, drug-seeking behavior, attention-seeking behavior, paranoia, sudden panic, anxiety, hallucinations|
|Electrolyte disturbance||Fatigue, headache, nausea||Varies depending on deficient ions; clinically, edema, constipation, hallucinations; on EKG, abnormalities in T wave, P wave, QRS complex; possible presentations include arrhythmia, dehydration, renal failure|
|Stroke||Ataxia, aphasia, dizziness||Varies depending on classification of stroke; presents with positional vertigo, high blood pressure, extremity weakness|
|Intracranial hemorrhage||Headache, coma, dizziness||Lobar hemorrhage, numbness, tingling, hypertension, hemorrhagic diathesis|
|Trauma||Headache, altered mental status||Amnesia, loss of consciousness, dizziness, concussion, contusion|
Herpes simplex encephalitis must be differentiated from other causes of headache, altered mental status and seizures such as brain tumors and delirium trmemns.
|Diseases||Diagnostic tests||Physical Examination||Symptoms||Past medical history||Other Findings|
|Na+, K+, Ca2+||CT /MRI||CSF Findings||Gold standard test||Neck stiffness||Motor or Sensory deficit||Papilledema||Bulging fontanelle||Cranial nerves||Headache||Fever||Altered mental status|
|Brain tumour||?||Cancer cells||MRI||?||?||?||?||?||?||Cachexia, gradual progression of symptoms|
|Delerium Tremens||?||Clinical diagnosis||?||?||?||?||?||?||Alcohal intake, sudden witdrawl or reduction in consumption||Tachycardia, diaphoresis, hypertension, tremors, mydriasis, positional nystagmus, tachypnea|
|Subarachnoid hemorrhage||?||Xanthochromia||CT scan without contrast||?||?||?||?||?||?||?||?||Trauma/fall||Confusion, dizziness, nausea, vomiting|
|Stroke||?||Normal||CT scan without contrast||?||?||?||?||?||TIAs, hypertension, diabetes mellitus||Speech difficulty, gait abnormality|
|Neurosyphilis||?||? Leukocytes and protein||CSF VDRL-specifc
CSF FTA-Ab -sensitive
|?||?||?||?||?||?||Unprotected sexual intercourse, STIs||Blindness, confusion, depression,
|Viral encephalitis||?||Increased RBCS or xanthochromia, mononuclear lymphocytosis, high protein content, normal glucose||Clinical assesment||?||?||?||?||?||?||?||Tick bite/mosquito bite/ viral prodome for several days||Extreme lethargy, rash hepatosplenomegaly, lymphadenopathy, behavioural changes|
|Herpes simplex encephalitis||?||Clinical assesment||?||?||?||?||?||History of hypertension||Delirium, cortical blindness, cerebral edema, seizure|
|Wernicke’s encephalopathy||Normal||?||?||?||History of alcohal abuse||Ophthalmoplegia, confusion|
|CNS abscess||?||? leukocytes >100,000/ul, ? glucose and ? protien, ? red blood cells, lactic acid >500mg||Contrast enhanced MRI is more sensitive and specific,
Histopathological examination of brain tissue
|?||?||?||?||?||?||?||History of drug abuse, endocarditis, ? immune status||High grade fever, fatigue,nausea, vomiting|
|Drug toxicity||?||?||Lithium, Sedatives, phenytoin, carbamazepine|
|Conversion disorder||Diagnosis of exclusion||?||?||?||?||?||Tremors, blindness, difficulty swallowing|
|Electrolyte disturbance||? or ?||Depends on the cause||?||?||Confusion, seizures|
|Febrile seizures||Not performed in first simple febrile seizures||Clinical diagnosis and EEG||?||?||?||?||Family history of febrile seizures, viral illness or gastroenteritis||Age > 1 month,|
|Subdural empyema||?||Clinical assesment and MRI||?||?||?||?||?||?||History of relapses and remissions||Blurry vision, urinary incontinence, fatigue|
|Hypoglycemia||? or ?||Serum blood glucose||?||?||?||History of diabetes||Palpitations, sweating, dizziness, low serum, glucose|
Epidemiology and Demographics
The incidence of herpes simplex encephalitis is approximately 0.1-0.2 per 100,000 individuals worldwide. Approximately 2,000 cases of herpes simplex encephalitis occur within the United States annually. Approximately 90% of cases are caused by HSV-1, with 10% caused by HSV-2. HSV-2 infection is most commonly observed among immunocompromised individuals and neonates.
Approximately 50% of individuals who develop herpes simplex encephalitis are over 50 years of age.
There is no gender predilection to the development of herpes simplex encephalitis.
There is no racial predilection to the development of herpes simplex encephalitis.
Unlike other cases of encephalitis, there is no seasonal predilection to the development of herpes simplex encephalitis.
Natural History, Complications and Prognosis
Common complications of herpes simplex encephalitis include:
- Increased intracranial pressure
- Aspiration pneumonia
- Respiratory failure
The 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.
History and Symptoms
If possible, a detailed and thorough history from the patient is necessary. Symptoms of herpes simplex encephalitis include:
- Decreased alertness
- Inability to produce or comprehend language
- Difficulty swallowing
Physical examination findings for herpes simplex encephalitis are generally unspecific. Common physical examination findings of herpes simplex encephalitis include:
- Erythema multiforme
- Genital and/or oral ulcers
Laboratory findings consistent with the diagnosis of herpes simplex encephalitis include increased leukocytes in cerebrospinal fluid obtained via lumbar puncture. 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 one day after symptoms first appear and lasting up to one week after treatment.
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. Subtleties become more apparent over time and may progress to hemorrhage, and may eventually spread to the other temporal lobe after 7-10 days.
- T1 C+ (Gd)
- Early, enhancement is generally absent
- Later, enhancement is variable and may appear as:
- Gyral enhancement
- Leptomeningeal enhancement
- Ring enhancement
- Diffuse enhancement
- May demonstrate blooming if hemorrhagic
The following video demonstrates herpes simplex encephalitis on MRI:
The mainstay of therapy for herpes simplex encephalitis includes antiviral therapy. The drug of choice is acyclovir. Supportive therapy for herpes simplex encephalitis includes breathing assistance, intravenous fluids, anti-inflammatory drugs, and anticonvulsant medication.
Effective measures for the primary prevention of herpes simplex encephalitis include abstinence from sexual contact, remaining 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.
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