Japanese encephalitis
Updates to Article Attributes
Japanese encephalitis (JE) is one of many viral encephalitides and results from infection with the Japanese encephalitis virus.
Clinical presentation
At the onset of the disease patients present with severe rigors, fevers and headache. As it progresses to the acute encephalitic stage, meningo-encephalitic symptoms such as neck rigidity, cachexia, hemiparesis and convulsions become prevalent.
Pathology
JEJapanese encephalitis is caused by the JEJapanese encephalitis virus, a single-stranded RNA flavivirus. Domestic pigs and wild birds are reservoirs for the virus, which is spread by mosquitoes. It is prevalent in India, Southeast Asia and East Asia 5.
Radiographic features
Bilateral thalamic involvement is classical regardless of CT or MR imaging. Other areas may be involved are midbrain, pons, cerebellum, basal ganglia, cerebral cortex and spinal cord. However, imaging within 3-4 days of the onset of disease may not reveal haemorrhagic lesions.
CT
symmetric or asymmetric bilateral thalamic hypodensities
may not detect subacute or chronic haemorrhage
MRI
-
parenchymal oedema in affected regions:
DWI: variable restricted diffusion
T1: low signal
T2/FLAIR: high signal
-
if haemorrhage is present:
GRE: patchy blooming
Treatment and prognosis
Only supportive treatment is available. Higher mortality rate in children. Vaccination may be preventive in endemic areas, although infection with JEJapanese encephalitis confers lifelong immunity.
Differential diagnosis
Other infectious causes that can cause a similar imaging pattern include:
other flavivirus encephalitides (e.g. Murray Valley encephalitis, West Nile fever, dengue encephalitis)
-
it is important to differentiate
JEJapanese encephalitis from herpes simplex encephalitis, as the latter can be treated with antiviralsalthough typically temporal lobe involvement
Causes of T2 hyperintense basal ganglia lesions can also be considered.
Haemorrhagic thalamic lesions can also be a result of:
deep cerebral vein thrombosis
basilar artery thrombosis: rarely tentorial herniation following head injury may cause thalamic infarcts
Practical points
Radiologists may face a diagnostic challenge when CT/MRI findings of both JEJapanese encephalitisandneurocysticercosis(NCC)are seen in the same patient.1.
Theoretically, both JEJapanese encephalitis and NCCneurocysticercosis share some common epidemiological factors; and in both conditions, pig acts as the intermediate carrier. Studies show that the occurrence of JEJapanese encephalitis and NCCneurocysticercosis in the same patient is not just a coincidence, albeit, NCCneurocysticercosis predisposes a person to JEJapanese encephalitis infection. Keeping in mind this fact may help radiologists and clinicians in proper and early management of the patient who present with mixed clinical scenario.
-<p><strong>Japanese encephalitis (JE) </strong>is one of many <a href="/articles/viral-encephalitides">viral encephalitides</a> and results from infection with the Japanese encephalitis virus.</p><h4>Clinical presentation</h4><p>At the onset of the disease patients present with severe rigors, fevers and headache. As it progresses to the acute encephalitic stage, meningo-encephalitic symptoms such as neck rigidity, cachexia, hemiparesis and convulsions become prevalent. </p><h4>Pathology</h4><p>JE is caused by the JE virus, a single-stranded RNA flavivirus. Domestic pigs and wild birds are reservoirs for the virus, which is spread by mosquitoes. It is prevalent in India, Southeast Asia and East Asia <sup>5</sup>. </p><h4>Radiographic features</h4><p>Bilateral thalamic involvement is classical regardless of CT or MR imaging. Other areas may be involved are midbrain, pons, cerebellum, basal ganglia, cerebral cortex and spinal cord. However, imaging within 3-4 days of the onset of disease may not reveal haemorrhagic lesions.</p><h5>CT</h5><ul>-<li>symmetric or asymmetric bilateral thalamic hypodensities</li>-<li>may not detect subacute or chronic haemorrhage</li>- +<p><strong>Japanese encephalitis (JE) </strong>is one of many <a href="/articles/viral-encephalitides">viral encephalitides</a> and results from infection with the Japanese encephalitis virus.</p><h4>Clinical presentation</h4><p>At the onset of the disease patients present with severe rigors, fevers and headache. As it progresses to the acute encephalitic stage, meningo-encephalitic symptoms such as neck rigidity, cachexia, hemiparesis and convulsions become prevalent. </p><h4>Pathology</h4><p>Japanese encephalitis is caused by the Japanese encephalitis virus, a single-stranded RNA flavivirus. Domestic pigs and wild birds are reservoirs for the virus, which is spread by mosquitoes. It is prevalent in India, Southeast Asia and East Asia <sup>5</sup>. </p><h4>Radiographic features</h4><p>Bilateral thalamic involvement is classical regardless of CT or MR imaging. Other areas may be involved are midbrain, pons, cerebellum, basal ganglia, cerebral cortex and spinal cord. However, imaging within 3-4 days of the onset of disease may not reveal haemorrhagic lesions.</p><h5>CT</h5><ul>
- +<li><p>symmetric or asymmetric bilateral thalamic hypodensities</p></li>
- +<li><p>may not detect subacute or chronic haemorrhage</p></li>
-<li>parenchymal oedema in affected regions:<ul>-<strong>DWI:</strong> variable restricted diffusion</li>-<li>-<strong>T1:</strong> low signal</li>-<li>-<strong>T2/FLAIR: </strong>high signal</li>- +<p>parenchymal oedema in affected regions:</p>
- +<ul>
- +<li><p><strong>DWI:</strong> variable restricted diffusion</p></li>
- +<li><p><strong>T1:</strong> low signal</p></li>
- +<li><p><strong>T2/FLAIR: </strong>high signal</p></li>
-<li>if haemorrhage is present:<ul><li>-<strong>GRE: </strong>patchy blooming</li></ul>- +<li>
- +<p>if haemorrhage is present:</p>
- +<ul><li><p><strong>GRE: </strong>patchy blooming</p></li></ul>
-</ul><h4>Treatment and prognosis</h4><p>Only supportive treatment is available. Higher mortality rate in children. Vaccination may be preventive in endemic areas, although infection with JE confers lifelong immunity.</p><h4>Differential diagnosis</h4><p>Other infectious causes that can cause a similar imaging pattern include:</p><ul>-<li>other <a title="Flavivirus encephalitides" href="/articles/flavivirus-encephalitis">flavivirus encephalitides</a> (e.g. <a href="/articles/murray-valley-encephalitis">Murray Valley encephalitis</a>, <a href="/articles/west-nile-fever">West Nile fever</a>, <a href="/articles/dengue-encephalitis">dengue encephalitis</a>)</li>-<li><a href="/articles/eastern-equine-encephalitis">eastern equine encephalitis</a></li>- +</ul><h4>Treatment and prognosis</h4><p>Only supportive treatment is available. Higher mortality rate in children. Vaccination may be preventive in endemic areas, although infection with Japanese encephalitis confers lifelong immunity.</p><h4>Differential diagnosis</h4><p>Other infectious causes that can cause a similar imaging pattern include:</p><ul>
- +<li><p>other <a href="/articles/flavivirus-encephalitis" title="Flavivirus encephalitides">flavivirus encephalitides</a> (e.g. <a href="/articles/murray-valley-encephalitis">Murray Valley encephalitis</a>, <a href="/articles/west-nile-fever">West Nile fever</a>, <a href="/articles/dengue-encephalitis">dengue encephalitis</a>)</p></li>
- +<li><p><a href="/articles/eastern-equine-encephalitis">eastern equine encephalitis</a></p></li>
-<a href="/articles/herpes-simplex-encephalitis">herpes simplex encephalitis</a><ul>-<li>it is important to differentiate JE from herpes simplex encephalitis, as the latter can be treated with antivirals</li>-<li>although typically temporal lobe involvement</li>- +<p><a href="/articles/herpes-simplex-encephalitis">herpes simplex encephalitis</a></p>
- +<ul>
- +<li><p>it is important to differentiate Japanese encephalitis from herpes simplex encephalitis, as the latter can be treated with antivirals</p></li>
- +<li><p>although typically temporal lobe involvement</p></li>
-<li>deep cerebral vein thrombosis</li>-<li>basilar artery thrombosis: rarely tentorial herniation following head injury may cause thalamic infarcts</li>-</ul><h4>Practical points</h4><p>Radiologists may face a diagnostic challenge when CT/MRI findings of both JE<strong> </strong>and<strong> </strong><a href="/articles/neurocysticercosis">neurocysticercosis</a><strong> </strong>(NCC)<strong> </strong>are seen in the same patient.<sup>1</sup></p><p>Theoretically, both JE and NCC share some common epidemiological factors; and in both conditions, pig acts as the intermediate carrier. Studies show that the occurrence of JE and NCC in the same patient is not just a coincidence, albeit, NCC predisposes a person to JE infection. Keeping in mind this fact may help radiologists and clinicians in proper and early management of the patient who present with mixed clinical scenario.</p>- +<li><p>deep cerebral vein thrombosis</p></li>
- +<li><p>basilar artery thrombosis: rarely tentorial herniation following head injury may cause thalamic infarcts</p></li>
- +</ul><h4>Practical points</h4><p>Radiologists may face a diagnostic challenge when CT/MRI findings of both Japanese encephalitis<strong> </strong>and<strong> </strong><a href="/articles/neurocysticercosis">neurocysticercosis</a><strong> </strong>(NCC)<strong> </strong>are seen in the same patient <sup>1</sup>.</p><p>Theoretically, both Japanese encephalitis and neurocysticercosis share some common epidemiological factors; and in both conditions, pig acts as the intermediate carrier. Studies show that the occurrence of Japanese encephalitis and neurocysticercosis in the same patient is not just a coincidence, albeit, neurocysticercosis predisposes a person to Japanese encephalitis infection. Keeping in mind this fact may help radiologists and clinicians in proper and early management of the patient who present with mixed clinical scenario.</p>
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