Acute Encephalitis

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Acute encephalitis constitutes a neurological emergency and it is imperative that appropriate treatment is started as soon as possible based on the likely clinical diagnosis. Take expert neurological advice.

About

• Viral encephalitis is a medical emergency.
• Inflammation of brain parenchyma often due to invasion by viruses
• Prognosis depends mainly on the pathogen and host immunologic state.
• For HSV encephalitis early diagnosis and treatment has a dramatic influence upon survival and reduces the extent of permanent brain injury.

Infectious Causes

• UK: Herpes simplex Virus I/II, Varicella zoster.
• World: HSV/VZ, Japanese Encephalitis virus, West Nile virus
• RNA virus : Lassa fever, Hanta, Viral haemorrhogic fevers

Other Causes

• ADEM, postinfectious/vaccination encephalomyelitis
• Autoimmune encephalitis

Differentials

• Encephalopathy - ammonia, alcoholic
• Hashimotos - Anti Thyroid antibodies
• HIV test / CD4 etc. if PML

Clinical (mostly refers to HSV)

• Wide range from well and acutely dysphasic to comatose
• Seizures (temporal lobe), fever, headache, weakness
• Well with acute dysphasia due to temporal lobe involvement I have seen
• Comatose, delirium others just focal signs
• Rigidity, Chorea: Japanese encephalitis
• Rash: HHV6 and Zoster

Investigations

• FBC: Raised WCC, raised CRP
• U&E: check renal function before Aciclovir
• CSF : clear, 10-700 Lymphocytes and raised normal and positive PCR for HSV. enteroviral PCR or WNV (West Nile virus) if suspected
• CT: may show some temporal hypodensity or haemorrhage
• MRI: may demonstrate hyperintense areas on the T2-weighted image (T2WI), fluid-attenuated inversion recovery (FLAIR), or diffusion-weighted images, and T1-weighted image (T1WI) with gadolinium enhancement on temporal lobes, cingulate gyrus, orbitofrontal, and insular cortex. Haemorrhage can develop. HSV causes temporal lobe disease, Japanese virus affects basal ganglia
• EEG: temporal lobe involvement

Differential

• Acute Stroke
• Tumour
• Acute disseminated encephalomyelitis (ADEM)

Management

• ABC, ITU if raised ICP and severe disease
• Aciclovir 10mg/kg iv every 8 hours for 14 days reduces mortality 70% to 20%. Give until CSF PCR nil or expert advice to stop. If you have any suspicion of the diagnosis at all then treat with IV Aciclovir even if it turns out to be wrong. Untreated HSV is a tragedy. The duration of treatment is 21 days for immunosuppressed patients. Monitor renal function as can cause an AKI
• Ribavirin can be used if RNA virus encephalitis as listed above. Usually in endemic areas with Lassa fever and various haemorrhagic fevers
• Ganciclovir if HHV6 considered
• Monitor renal function, hydration and NG feeding as required. Often initially managed in HDU setting. Of those who survive there is a high risk of ongoing neurological deficits.
• There is no evidence base for steroids. Treat any seizures with usual drugs e.g. Keppra or Phenytoin
• Raised ICP to consider IV mannitol or mechanical hyperventilation
• Surgery: For the most severe cases hemicraniectomy may be needed for decompression or shunting for any hydrocephalus

Poor Prognostic features

• Age > 30
• Coma at presentation
• Bilateral EEG abnormalities
• High CNS viral load
• Treatment delayed (4 days)
• Abnormal CT

Late complications

• Poor memory, emotional lability
• Poor concentration, irritability, depression

References

• Viral meningoencephalitis: a review of diagnostic methods and guidelines for management
• Diagnosis and treatment of viral encephalitis A Chaudhuri, P G E Kennedy Postgrad Med J 2002;78:575-583