Dengue hemorrhagic encephalitis: MRI

History: 39 years male, known case of dengue with NS1 positive with altered sensorium.

MRI findings

Multiple ill defined, irregular, mild to moderately enhancing  mixed signal intensity lesions seen involving both thalami, pons, posterior midbrain, both frontoparietal  pariventricular white matter regions ( right thalamus & pons more than rest) with restricted diffusion   /reduced ADC values / patchy bright signal s on T1 / blooming on SW ( pons more than rest) with mass effect on 4^thventricle / mild proximal ventriculomegaly / moderate patchy meningeal  enhancement. Rest of the brain parenchyma & major dural  venous  sinuses  normal. Findings are likely suggestive of meningoencepalitis of dengue etiology, in view of history.

Discussion by Dr MGK Murthy, Dr GA Prasad

1. Dengue virus is a single-stranded RNA virus of the Flavivirus genus classified into four serotypes. Neurological manifestations, commonly seen with serotypes 2 and 3.
2. Neurological manifestation in dengue hemorrhagic fever usually results from multisystem dysfunction secondary to liver failure, cerebral hypoperfusion, electrolyte imbalance, shock, cerebral edema, and hemorrhage related to vascular leak.  Presentation as viral encephalitis is rare as the virus is non-neurotrophic.
3. Patients can  present with -  stroke, mononeuropathies, polyneuropathies, Guillain-Barre syndrome (GBS), myelitis, meningitis, acute disseminated encephalomyelitis (ADEM), encephalopathy, encephalitis, neuromyelitis optica, and optic neuritis.
4. Presence of dengue virus and anti-dengue IgM antibodies in patient's CSF with encephalitis suggests the possibility of direct cerebral invasion through infected macrophages.
5. Clinical differentials can be differentiated by MRI  -

•          Japanese encephalitis – bilateral thalamic and basal ganglia involvement .
•          Herpes encephalitis- bilateral temporal and basifrontal lobes lesions.
•         Chikungunya encephalitis - white matter lesions with restricted diffusion without hemorrhage or basal ganglia involvement.
•         Changes of ADEM in dengue fever are similar to Dengue  encephalitis on MRI and may not be possible to differentiate on MRI always.

There is no specific treatment for dengue encephalitis & treatment is mainly supportive.

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