This is mentioned in Sivakumar and Pelly's chapter on tropical diseases in Oh's Manual. Thus far, the College has not asked about it in the SAQs, and it has not appeared among the differentials suggested for a febrile patient with a decreased level of consciousness. All thing considered, its appearance in the CICM SAQs would therefore constitute a sadistic assault on the candidates. However, it would not be the first such assault.
Apart from Oh's Manual, there is some good literature available on this topic:
- An entire book chapter on arboviral encephalitis.
- Another whole book chapter on arthropod-borne encephalitides (from which this summary is largely derived)
- A more useful broad overview of viral encephalitis in returning travellers.
Virology of arboviral encephalitis
- Numerous viruses could be the cause.
- Usually some sort of arthropod vector is involved.
- Subtypes include:
- Japanese encephalitis
- West Nile virus encephalitis
- St Louis encephalitis
- Murray Valley encephalitis
- A classical presentation would be a complaint of a tick bite.
- Alternatively, the patient's history might suggest arthropod exposure, i.e. being in the company of ticks in context of hiking or bushwalking.
- Incubation period is 5–15 days.
- Triad of (non-specific) features:
- Decreased level of consciousness
- Usually, a flu-like illness is the prodrome
- Other associated features:
- Behavioural disturbance, initially misdiagnosed as psychiatric illness
- Focal neurological signs
- Seizures, potentially status epilepticus
- Flaccid paralysis (the spinal cord may also be affected)
- Parkinson-like movement disorders
Characteristic findings on investigation
- Hyponatremia due to SIADH
- CSF lymphocytosis and elevated protein
- MRI: high signal intensity in the thalamus and basal ganglia
- CT is frequently pointless
- EEG may do nothing other than exclude seizures
- Characteristic serology findings and antigen identification is diagnostic.
- Again, "supportive" management is the only thing one can offer.
- Frequently the decreased level of consciousness will mandate intubation, but infrequently is there any specific ICU management issue, beyond invasive ventilation, and the maintenance of the status quo.
- Protecting the patient from the consequences of immobility and ventilation are therefore management priorities.
- On occasion, there will be oedema-related increased intracranial pressure, which would then be monitored and managed in a manner similar to the oedema of traumatic brain injury.
As for experimental treatments, the literature lists the following:
- Interferon alpha
- Intravenous immunoglobulins
This is generally based on case reports, in vitro studies and animal data.