Summary

Viral Encephalitis is an acute inflammation of the brain parenchyma, distinct from meningitis (inflammation of the linings). It presents with fever, headache, and prominence of altered mental status (confusion, personality change, psychosis) and focal neurological signs (seizures, dysphasia). The most common sporadic cause of fatal encephalitis is Herpes Simplex Virus Type 1 (HSV-1). Treatment with IV Aciclovir must be started immediately on suspicion, often before LP, as mortality reduces from 70% to 20% with early treatment. Autoimmune Encephalitis (e.g. Anti-NMDA) is a key differential diagnosis in young patients.

Key Facts

• Definition: Inflammation of brain parenchyma (Encephalitis) vs linings (Meningitis).
• Top Pathogen: HSV-1 is the most common treatable cause.
• Classic HSV Signs: Temporal lobe predilection -> Dysphasia, Olfactory hallucinations, Memory loss, Personality change.
• Treatment: IV Aciclovir 10mg/kg TDS. Start empirically.
• Mortality: 70% if untreated; 20-30% if treated.
• Sequelae: High rates of memory impairment and epilepsy.

Clinical Pearls

"Meningitis vs Encephalitis":

• Meningitis: "My head hurts, light hurts, neck stiff" (Cognition usually intact early).
• Encephalitis: "Who are you? Why are there spiders?" (Cognition abnormal early + Seizures).

"The Psychiatric Presentation": A young person presenting with new onset psychosis/agitation with a fever/headache has Encephalitis until proven otherwise. Do not send to Psychiatry.

"Aciclovir is Nephrotoxic": It crystallises in renal tubules. Hydrate avidly (1L Saline with each dose or Ensure > 2-3L fluid intake).

         SUSPECTED ENCEPHALITIS
       (Fever + Confusion + Headache)
                     ↓
          START IV ACICLOVIR
    (Do not wait for CT/LP results)
                     ↓
        CT HEAD (If low GCS/Focal)
           /                   \
      Mass Effect             Normal
         ↓                       ↓
    Treat ICP              LUMBAR PUNCTURE
    No LP yet              Send CSF PCR

1. Specific Antiviral Therapy

• HSV/VZV Suspected:
  • IV Aciclovir 10mg/kg TDS (Use ideal body weight in obesity).
  • Duration: 14-21 days.
  • Repeat LP: Some guidelines suggest repeating LP at day 21 to ensure PCR negative before stopping.
• CMV (Immunocompromised): Ganciclovir + Foscarnet.

2. Adjunctive Therapy

• Seizures: Levetiracetam / Phenytoin.
• Cerebral Edema: Consider Dexamethasone (Controversial, but often used if significant swelling).
• Antibiotics: Often started initially (Ceftriaxone) to cover bacterial meningitis until CSF proves otherwise.

3. Renal Protection

• Aciclovir crystals precipitate in renal tubules.
• Protocol: 1 Litre 0.9% Saline with each dose, or strict fluid balance aim >3L input/day. Check Creatinine daily.

"Brain on Fire" Often misdiagnosed as Viral Encephalitis or Schizophrenia.

• Classic Patient: Young female.
• Progression:
  1. Prodrome: Flu-like illness.
  2. Psychiatric: Anxiety, insomnia, rapid onset psychosis, mania.
  3. Initial Neuro: Memory loss, seizures.
  4. Late Neuro: Catatonia, Autonomic instability, Orofacial dyskinesias (chewing movements).
• Tests: CSF Anti-NMDAR antibodies. Whole Body CT/MRI (Look for Ovarian Teratoma).
• Treatment: Steroids (Methylprednisolone), IVIG, Plasma Exchange. Removal of teratoma.

Aciclovir (Acyclovir)

• Mechanism: Guanosine analogue. Converted to Aciclovir-Monophosphate by viral Thymidine Kinase (specific to virus infected cells). Then to Triphosphate by host enzymes. Inhibits viral DNA polymerase. Chain terminator.
• Selectivity: Only active in infected cells (need viral kinase).
• Dosing:
  • Encephalitis: 10 mg/kg TDS (High dose).
  • Normal: 5 mg/kg TDS.
• Adverse Effects:
  • Nephrotoxicity (Crystalluria).
  • Neurotoxicity (Tremor, confusion - esp in renal failure).
  • Phlebitis (IV site irritation).

The Long Road Back. Survival is good (80%), but full recovery is rare (<50%).

• Amnesia: Due to temporal lobe destruction (Hippocampus). "Korsakoff-like" syndrome. Inability to form new memories (Anterograde amnesia).
• Epilepsy: Scarring leads to structural epilepsy.
• Dysexecutive Syndrome: Frontal lobe damage. Personality change, apathy, disinhibition.
• Management:
  • Neuropsychology assessment.
  • Memory aids / Occupational Therapy.
  • Family support (Personality change is hardest for relatives).

Key Guidelines

• Association of British Neurologists (ABN) / British Infection Association (BIA): National Guidelines for Management of Encephalitis (2012).
• Infectious Diseases Society of America (IDSA): Management of Encephalitis (2008).

Prognostic Data

• Untreated HSV: 70% Mortality.
• Treated HSV: 10-20% Mortality.
• Morbidity: >50% have moderate/severe cognitive deficits.
• Delays: Every hour delay in Aciclovir increases risk of poor outcome.

What is Encephalitis?

Encephalitis is inflammation of the brain itself (the brain swelling). It is usually caused by a virus infection. It is rare but very serious.

Is it the same as Meningitis?

No. Meningitis is swelling of the lining around the brain. Encephalitis is swelling of the actual brain. Encephalitis tends to affect thinking, memory, and personality more than meningitis.

What causes it?

The cold sore virus (Herpes Simplex) is the most common cause. It usually wakes up from sleeping in a nerve and travels to the brain. It is NOT usually caught from someone else.

How is it treated?

It is treated with a strong antiviral medicine called Aciclovir into a vein. This stops the virus multiplying. Treatment lasts for 2-3 weeks.

Will they recover?

Most people survive with treatment. However, because the brain is affected, many people have long-term problems with short-term memory, tiredness, or concentration. It can take months or years to reach maximum recovery.