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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.

Initial Encephalitis Management Summary
ABC, Admit for LP. CT if any signs suggesting SOL, Bloods +/- CSF cultures. Start IV Aciclovir 10 mg/kg TDS initially if HSV Encephalitis considered MRI is useful to support diagnosis. Neurology consult. IV Cefotaxime if Meningitis considered at presentation and awaiting results

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.

Causes

Cause	Clinical Features	Investigations	Treatment
Viral Encephalitis (e.g., HSV-1, HSV-2, Varicella Zoster Virus)	Fever Headache Altered mental status Seizures Focal neurological deficits (e.g., hemiparesis, aphasia)	Cerebrospinal fluid (CSF) analysis: Increased WBCs, elevated protein, normal glucose, PCR for viral DNA MRI brain: Temporal lobe hyperintensities (especially in HSV encephalitis) Electroencephalogram (EEG): Temporal lobe epileptiform activity	Intravenous Aciclovir (especially for HSV, VZV) Supportive care (hydration, antipyretics) Anticonvulsants if seizures are present
Autoimmune Encephalitis (e.g., Anti-NMDA receptor encephalitis)	Psychiatric symptoms (e.g., agitation, hallucinations) Memory deficits Seizures Dyskinesias Autonomic instability	CSF analysis: Mild pleocytosis, elevated protein, oligoclonal bands Anti-NMDA receptor antibodies in serum and CSF MRI brain: Often normal or nonspecific changes EEG: Diffuse slowing, epileptiform discharges	Immunotherapy: First-line treatment includes corticosteroids, IVIG, or plasmapheresis Second-line immunosuppressants (e.g., rituximab, cyclophosphamide) if refractory Treat underlying neoplasm if paraneoplastic
Bacterial Encephalitis (e.g., Listeria, Mycoplasma)	Fever Headache Confusion Focal neurological signs Seizures (less common than in viral causes)	CSF analysis: Elevated WBCs, high protein, low glucose, Gram stain, and culture MRI brain: May show focal lesions or abscess formation Blood cultures to identify the organism	Appropriate intravenous antibiotics (e.g., ampicillin for Listeria) Supportive care (hydration, monitoring) Treat complications such as increased intracranial pressure (ICP)
Fungal Encephalitis (e.g., Cryptococcus, Aspergillus)	Fever Headache Meningismus Altered mental status Cranial nerve palsies	CSF analysis: Elevated WBCs, high protein, low glucose, India ink staining for Cryptococcus Cryptococcal antigen test in CSF or serum MRI brain: May show nodular lesions or abscesses	Antifungal therapy (e.g., amphotericin B plus flucytosine for Cryptococcus) Long-term oral fluconazole for maintenance therapy Management of increased ICP if present
Parasitic Encephalitis (e.g., Toxoplasmosis, Malaria)	Fever Headache Confusion Seizures Focal neurological signs	CSF analysis: May show elevated WBCs, protein, low glucose, specific PCR for pathogens Serology for specific parasites (e.g., Toxoplasma IgG/IgM) MRI brain: Ring-enhancing lesions (e.g., in toxoplasmosis)	Antiparasitic therapy (e.g., pyrimethamine and sulfadiazine for Toxoplasmosis) Supportive care (hydration, antipyretics) Treat complications such as seizures with anticonvulsants
Toxic/Metabolic Encephalopathy	Confusion or altered mental status Tremors, asterixis Seizures Coma in severe cases History of exposure to toxins or metabolic imbalance (e.g., hypoglycemia, uraemia)	Blood tests: Electrolytes, liver function tests, renal function, toxicology screen CSF analysis usually normal unless secondary infection Imaging: May show cerebral edema in severe cases	Treat underlying cause (e.g., glucose for hypoglycemia, dialysis for uraemia) Supportive care in ICU for severe cases Seizure management with anticonvulsants if needed

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

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