encephalitis

Question 1

definition

Answer 1

inflammation of the brain parenchyma with the presence of clinically evident neurological dysfunction

Question 2

aetiology

Answer 2

aetiology = viral/non-viral

The most usual cause of encephalitis in the UK is herpes simplex virus.

HIV infection is of increasing importance.

Other causes of encephalitis include:

• measles
• mumps
• rabies
• tick-borne encephalitis
• poliomyelitis
• varicella
• subacute sclerosing panencephalitis
• progressive multifocal leucoencephalopathy
• California bunyavirus
• Coxsackie virus
• cytomegalovirus
• Echo virus
• herpes zoster
• Behcet’s syndrome

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• Viruses are the most common cause of encephalitis but sometimes bacteria and other organism (Rickettsiae, Fungi) may also cause encephalitis
• The principal viral agent is herpes simplex which affects primarily the temporal lobes to give a bilateral low density region on CT scan. The major complication of encephalitis is a severe amnesic syndrome caused by profound damage to the temporal lobes.
• Encephalitis can be divided into:
  
  • Primary encephalitis or acute viral encephalitis
  • Secondary encephalitis or post-infective encephalitis
• Most viral infections in childhood are able to cause encephalitis. Acute encephalitis is a notifiable disease in the UK

Question 3

clinical features

Answer 3

Encephalitis presents in a similar manner to an abscess:

a short history of:

• headache
• pyrexia
• confusion
• vomiting
• an important negative is the absence of neck stiffness

developing into:

• epilepsy
• focal neurological signs
• cognitive impairment

Clues to the origin of the encephalitis may be ascertained from the presentation:

1. chickenpox encephalitis often has cerebellar involvement
2. Herpes simplex encephalitis often presents with a fit and the most often involves the temporal lobe

Question 4

investigation of encephalitis should include:

Answer 4

• a physical examination - which includes a detailed neurological examination
• a medical history - activities of the past several days (to detect any contact with insects, animals or recent travel)
• throat swabs, stool culture
• CT - a late sign is bilateral low density regions in both temporal lobes seen with herpes simplex encephalitis; not very useful for early diagnosis, but essential before lumbar puncture
• MRI - most sensitive investigation method in patients with encephalitis
• lumbar puncture after CT screening: usually shows raised protein and lymphocytic pleocytosis - identify organism; polymerase chain reaction now available at specialist centres for identification of organism. There may be oligoclonal bands in the CSF
• viral and immunological studies of serum and CSF; paired studies are required to show rising titres.
• EEG - in herpetic encephalitis, the EEG shows diffuse slowing with periodic discharges; this is more useful than a CT scan in the first week.
  
  • The EEG in encephalitis is characterized by generalized, large, slow waves.
  • The smaller the EEG waves become, the worse the prognosis for recovery.

Question 5

rx

Answer 5

Treatment is usually empirical to begin with, unless there is a clear idea of the aetiology. Thus, modalities include:

• intravenous acyclovir, to cover herpes simplex. Given before the patient enters coma, this treatment has massively improved the prognosis.
• intravenous broad spectrum antibiotics
• intravenous mannitol, to reduce cerebral oedema
• intravenous dextrose or dextrose sailine, to maintain the blood glucose. The usual fluid management is restriction to two thirds maintenance, again to reduce cerebral oedema.

supportive measures: HDU/ITU

symptomatic rx: phenytoin for seizures

Question 6

complications

Answer 6

In addition to the features of natural progression of the disease, a number of other sequalae may be observed:

• syndrome of inappropriate antidiuretic hormone
• disseminated intravascular coagulation
• cardiac and respiratory arrest

Long term complications can affect nearly any neurological system.

Question 7

prognosis

Answer 7

The prognosis of encephalitis is good in most patients, but depends on the age of the patient and the underlying aetiology the time taken for the initiation of treatment.

Most patients with mild encephalitis make a full recovery

The poorest prognosis for viral encephalitis occurs in patients with herpes simplex encephalitis and subacute sclerosing panencephalitis.

Question 8

ddx

Answer 8

• encephalopathy
• hypoglycemia
• hepatic encephalopathy
• DKA
• drugs
• hypoxic brain injury
• uraemia
• SLE
• beri beri [vit B1 deficiency]

Question 9

herpes simplex encephalitis: define

Answer 9

Herpes simplex (HSV) encephalitis is a common topic in the exam. The virus characteristically affects the temporal lobes - questions may give the result of imaging or describe temporal lobe signs e.g. aphasia

Question 10

herpes simplex encephalitis: s/s

Answer 10

Features

fever, headache, psychiatric symptoms, seizures, vomiting

focal features e.g. aphasia

peripheral lesions (e.g. cold sores) have no relation to presence of HSV encephalitis

Question 11

herpes simplex encephalitis pathophys

Answer 11

Pathophysiology

HSV-1 responsible for 95% of cases in adults

typically affects temporal and inferior frontal lobes

Question 12

herpes simplex encelphalitis ix

Answer 12

Investigation

CSF: lymphocytosis, elevated protein

PCR for HSV

CT: medial temporal and inferior frontal changes (e.g. petechial haemorrhages) - normal in one-third of patients

MRI is better

EEG pattern: lateralised periodic discharges at 2 Hz

Question 13

herpes simplex encephalitis: rx

Answer 13

Treatment

intravenous aciclovir

The prognosis is dependent on whether aciclovir is commenced early. If treatment is started promptly the mortality is 10-20%. Left untreated the mortality approaches 80%