Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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June 6, 2024
Murray Valley Encephalitis
- Background:
- Murray Valley encephalitis virus (MVEV) is a notifiable mosquito-borne virus endemic to northern Australia during wet seasons. MVEV is transmitted primary via Culex annulirostris mosquitoes with waterbirds as reservoirs.
- Clinical Presentation:
- Only 0.01–0.06% of infected patients develop Murray Valley encephalitis (MVE), which begins with a 1-week prodrome of fevers, headache, and gastrointestinal upset. Patients then follow 1 of 4 distinct courses:
- Encephalitis followed by complete recovery
- Brainstem involvement with cranial nerve palsies and tremor
- Spinal cord involvement with flaccid paralysis; or
- Relentless progression leading to death (15–30%)
- Only 0.01–0.06% of infected patients develop Murray Valley encephalitis (MVE), which begins with a 1-week prodrome of fevers, headache, and gastrointestinal upset. Patients then follow 1 of 4 distinct courses:
- Key Diagnostic Features:
- Foci of susceptibility artifact can be seen due to hemorrhage and necrosis
- Early symmetrical bilateral thalamic lesions later progressing to the brainstem, often causing mass effect and obstructive hydrocephalus
- Lesions are classically hypodense on CT and have high T2-weighted signal, high diffusion signal, low T1-weighted signal, and variable contrast enhancement on MRI
- Differential Diagnosis:
- Similar neuroradiologic MRI findings:
- Toxic leukoencephalopathy, which is characterized by confluent and symmetrical white matter abnormalities involving the corpus callosum and splenium on FLAIR and DWI. There may also be scattered punctate periventricular white matter microhemorrhages on SWI, and abnormal T1 contrast enhancement
- Eastern equine encephalitis, which typically demonstrates asymmetrical bilateral basal ganglia and thalamic lesions that are hypodense on CT and have high T2-weighted signal on MRI
- Other flavivirus encephalitides (eg, Japanese encephalitis, West Nile fever, St Louis encephalitis), which are distinguished using microbiological testing (eg, serology, polymerase chain reaction)
- Similar neuroradiologic MRI findings:
- Treatment:
- There is no known antiviral treatment, so supportive treatments include corticosteroids, antiepileptics, and ventilatory support. Preventative measures including vector control, personal protective equipment, and epidemiologic surveillance using sentinel chicken flocks remain essential.
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