Herpes Simplex Encephalitis

Herpes simplex virus: (HSV) may cause

• Acute necrotising encephalitis

• Disseminated HSV: Foci of necrosis in the brain associated with similar lesions in other organs

• Aseptic meningitis

Brain infection is thought to occur primarily from direct neuronal transmission of the virus from a peripheral site to the brain via the trigeminal or olfactory nerve.

Herpes simplex encephalitis: (HSE) fulminate and often rapidly fatal…

• Usually due to HSV type 1 (95% in children and adults) but in immunosuppressed and neonates HSV type 2 can occur

• HSE may occur as an isolated CNS infection or as a single manifestation of disseminated multi-organ disease.

• In some cases HSE is thought to represent a reactivation of latent infection within the brain

Neonatal HSE:

• Severe generalized encephalitis in 50% of neonates born to mothers wit primary HSV infection (risk lower when mother has recurrent HSV type 2)

• Acquired by contact with infected genital secretions at the time of delivery.

Macroscopically: temporal lobes most severely affected; large irregular bilateral and asymmetrical areas of necrosis are often haemorrhagic, with congestion and oedema.

Microscopically:

• Pan necrosis with perivascular inflammation

• Intranuclear viral inclusion are present in neurons and glial cells (immunocytochemistry)

• Gliosis if patient survives

Epidemiology: HSE may be found in any age group…

• Commonest cause of sporadic encephalitis

• Account for about 10% of all encephalitis cases in US, and is a rapidly progressive disease with profound neurologic derangement

• Result of primary herpes simplex virus in about 1/3 of cases. The remaining cases are due to recurrent infection

Symptoms: typically include the following:

• Fever (90%)

• Headache (81%)

• Psychiatric symptoms (71%)

• Seizures (67%)

• Vomiting (46%)

• Focal weakness (33%)

• Memory loss (24%)

Other findings include altered mental status, photophobia, and movement disorders.

Diagnosis: of HSE relies on…

• Isolation of the virus (brain biopsy or CSF) by PCR

• Neuroradiology

Treatment: acyclovir is the most effective treatment; mortality rate may be significantly reduced (outcome influenced by clinical state of patient on star of treatment)…

• The mortality rate in untreated patients is 70%

• Among treated patients, the mortality rate is 19%, and more than 50% of survivors are left with moderate or severe neurological deficits

Category: Medicine Notes , Pathology Notes