Encephalitis

Question 1

What is the presentation of encephalitis?

Answer 1

• Fever, chills/rigors
• Headache, nausea & vomiting
• Focal neurological deficits
• Obtundation / Altered mental state
• Behavioral disturbance (consider possibility of HSV causing temporal lobe dysfunction)
• Seizures

Question 2

What are the pathogens that cause encephalitis?

Answer 2

Viral* (Most common): HSV, VZV, EBV, CMV, Enterovirus, HIV

• HSV is most common; affects TEMPORAL lobe on CT brain
• HSV1 most commonly causes encephalitis
• HSV2 most commonly causes meningitis

Bacterial: Listeria, mycobacteria, syphilis, mycoplasma pneumonia

Fungal: Cryptococcus

Parasites: Toxoplasma (protozoa)

Question 3

What are the investigations required for encephalitis?

Answer 3

Bloods: FBC, PT/PTT, UECr, Blood culture

LP: CSF opening pressure, cell count with differential, glucose, protein

LP: CSF gram stain, cultures and PCR.

• Send for HSV / VZV PCR
• Detection of specific viral IgM antibodies is considered to be diagnostic of neuroinvasive disease
• Consider serology for certain viruses (West nile, rabies, Toxoplasma)

Brain MRI

• Identify anatomical sites affected
• CT scan only if MRI unavailable or cannot be performed
• Brain biopsy should only be done in patients with encephalitis of unknown etiology whose conditions deteriorate despite acyclovir therapy

Question 4

What are the clinical features of HSV Encephalitis?

Answer 4

Usually involves the temporal lobe, leading to:

• Seizures
• Visual defects – upper quadrantanopia
• Aphasia (if dominant lobe)
• Amnesia

Question 5

What is the management of encephalitis?

Answer 5

Empiric therapy

• Empirical Acyclovir therapy is always initiated in all patients with suspected encephalitis pending results of diagnostic studies.
• Patients who present with clinical/epidemiological clues of rickettsial infection should be treated empirically with doxycycline
• If patient is presumed to have bacterial meningoencephalitis start on empiric therapy as well

Confirmed HSV / VZV encephalitis – Acyclovir 10mg/kg IV q8hr

Confirmed CMV encephalitis – ganciclovir +/- foscarnet