Flavivirus encephalitis

Flavivirus encephalitis (plural: encephalitides) includes a number of entities which characteristically involve the basal ganglia and thalami. 

Clinical presentation

Typically these conditions present with a prodrome which is non-specific but highly suggestive of a viral infection. Symptoms include fever, myalgia, rash, rigors and/or headache. Eventually, CNS symptoms develop, including dystonia, dyskinesia, tremor, drooling, dysarthria and/or seizures ¹.

Pathology

There are over 70 flaviviruses. The most important include ^1-3:

• dengue encephalitis
• Japanese encephalitis virus (Asia)
• Murray Valley encephalitis virus (Australia; New Zealand; Papua New Guinea)
• Powassan virus (North America; Russian Far East)
• Rocio virus (Brazil)
• Saint Louis encephalitis virus (North America; South America)
• tick-borne encephalitis virus
• West Nile virus (Middle East; North America)

Radiographic features

MRI is the modality of choice to evaluate all types of encephalitis.

MRI

Although the pattern of involvement varies from agent to agent, in general, sites of involvement include ¹:

• T2 hyperintensity in the basal ganglia and/or thalami
• restricted diffusion in the basal ganglia and/or thalami
• hemorrhage is sometimes seen