CNS infection: Encephalitis (hsv-1 = Viral!!!)

Question 1

Definition

Answer 1

Encephalitis describes inflammation of the brain parenchyma. The most common cause of encephalitis is herpes simplex virus-1 (95% of cases), which causes temporal and inferior frontal lobe encephalitis.

Question 2

Epidemiology

Answer 2

Immunocompromise:
- numerous causes including extremes of age (children and the elderly),
- infection (such as HIV)
- medication (such as chemotherapy)

Question 3

Risk Factors

Answer 3

Blood/fluid exposure: HIV and West Nile virus
Mosquito bite: West Nile virus
Transfusion and transplantation: CMV, EBV, HIV
Close contact with cats: toxoplasmosis

Question 4

Aetiology

Answer 4

HSV1(95%)
HSV2

Question 5

Signs

Answer 5

Pyrexia
Reduced GCS
Focal neurological deficit, such as:
- Aphasia
- Hemiparesis
- Cerebellar signs

Question 6

Symptoms

Answer 6

Fever
Headache
Behavioural changes:
- Memory disturbance
- Psychotic behaviour
- Withdrawal or change in personality
Confusion
Seizures

Question 7

Diagnosis

Answer 7

Blood tests: FBC, CRP, U&Es and blood culture
Throat swab: culture for viral organisms
CT or MRI head: MRI is preferred and will show evidence of inflammation in the medial temporal and inferior frontal lobes in HSV encephalitis; CT is normal in ⅓ of cases
CSF investigations:
Analysis: lymphocytosis with raised protein in the case of viral aetiology
PCR: assays for common viral infections including HSV should be carried out
Culture: useful for bacterial causes
Serology: antibodies against specific viral antigens

Question 8

Management

Answer 8

Antiviral medication:
- ACICLOVIR should be commenced empirically in all patients with suspected encephalitis
- Ganciclovir may be preferred in other herpesvirus infections, such as HHV-6
A combination of ganciclovir and foscarnet is usually used in CMV

Question 9

Complications

Answer 9

Neurological sequelae: such as aphasia and neuropsychiatric issues
Seizures
Ischaemic stroke
Hydrocephalus