Encephalitis

Question 1

What is encephalitis?

Answer 1

Inflammation of the brain parenchyma

Question 2

Describe the aetiology of encephalitis

Answer 2

• Most commonly due to viral infection → Herpes Simplex Virus Type 1 most common in UK
• Can also be due to bacterial, fungal and parasitic infections.
• Also in immunocompromised patients or patients with autoimmune/paraneoplastic syndromes.

Question 3

What are the risk factors for encephalitis?

Answer 3

age under 1 or over 65 years, immunosuppression, viral infections, body fluid exposure, organ transplantation, animal or insect bites, travel, and season

Question 4

What viruses/ bacteria cause encephalitis?

Answer 4

● Most commonly due to VIRAL INFECTION
1. Viral Causes
o Herpes Simplex Virus - MOST COMMON in the UK
o VZV
o Mumps
o Adenovirus
o Coxsackie
o EBV
o HIV
o Japanese encephalitis
2. Non-Viral (RARE)
o Syphilis
o Staphylococcus aureus
3. In immunocompromised patients
o CMV
o Toxoplasmosis
o Listeria
4. Autoimmune or Paraneoplastic
o Associated with certain antibodies (e.g. anti-NMDA, anti-VGKC)

Question 5

Summarise the epidemiology of encephalitis

Answer 5

● UK incidence: 7.4/100,000
Bimodal age distribution → highest incidence in those <1 yr and >65 yrs

Question 6

What symptoms of encephalitis can a pt present with in the history?

Answer 6

● In most cases, encephalitis is self-limiting and mild
● Subacute onset (hours to days)
● Headache
● Fever
● Vomiting
● Altered mental state (differs from meningitis) → i.e., sudden change in behaviour (KEY DISTINGUISHING FACTOR FROM MENINGITIS)
● History of seizures
● Focal neurological symptoms (e.g. dysphagia, hemiplegia)
● Usually preceded by an infectious prodrome – fever, rash, lymphadenopathy, cold sores, conjunctivitis – before neurological signs
● Obtain a detailed TRAVEL HISTORY

Question 7

What signs of encephalitis can be found on physical examination?

Answer 7

● Reduce consciousness
● Bizarre encephalopathic behaviour
● Deteriorating GCS
● Seizures
● Pyrexia
Signs of Meningism:
*Neck stiffness
*Photophobia
*Kernig’s test positive
Signs of raised ICP:
*Cushing’s Response: hypertension + bradycardia + irregular breathing
*Papilloedema
● Focal neurological signs
● MMSE may reveal cognitive/psychiatric disturbance

Question 8

What investigations are used to diagnose/ monitor encephalitis?

Answer 8

1. CSF Analysis (Lumbar Puncture) → high lymphocytes, high protein, normal glucose
   - Viral = mononuclear cells (lymphocytes) predominate
   - Bacterial = polymorphonuclear cell (neutrophils) predominate
2. CSF Viral PCR → will confirm presence of HSV.
3. Bloods → increased WBCs, hyponatraemia, elevated LFTs
4. Blood Cultures → detect bacterial infection
5. Throat Swab → detection of viruses
6. MRI/CT Brain → exclude mass lesion, do CT scan prior to lumbar puncture to exclude significantly increased ICP
   - Bilateral medial temporal lobe involvement on MRI is strongly supportive of a diagnosis of encephalitis
   - CT Head showing temporal lobe changes = herpes simplex encephalitis

Question 9

How is encephalitis managed?

Answer 9

1. Suspected viral aetiology or confirmed HSV → IV Acyclovir + Supportive Care
2. Non-Viral Aetiology → Supportive Care + Treatment of underlying Aetiology (ie. antibiotics for bacterial encephalitis)

Question 10

What complications may arise from encephalitis?

Answer 10

Death, seizures, hypothalamic disfunction (SIADH, DI)