Japanese encephalitis lab diagnosis
"Japanese encephalitis" AND "laboratory diagnosis"
Japanese encephalitis MRI thalamus T2 hyperintensity
This longitudinal neuroimaging series tracks the progression of a brain injury, likely Japanese encephalitis, using T2-weighted MRI (A-B, D-F), non-contrast CT (C), T1-weighted MRI (G), and Diffusion Tensor Imaging (DTI) (H). Initial T2 MRI at day 6 (A, B) demonstrates symmetrical hyperintense signals in the bilateral thalamus, caudate nucleus, and cerebral peduncles (white arrows). By day 19, a CT scan (C) reveals a hyperdense region in the right thalamus consistent with an acute hemorrhage (arrow). Follow-up imaging at month 6 (D-F) and month 14 (G) shows the evolution into chronic sequelae: the primary lesions have reduced in size, but there is marked global brain atrophy characterized by prominent ventricles (ventriculomegaly), widened cortical sulci, and thinned gyri. The T1-weighted image (G) reinforces the presentation of diffuse atrophic changes. Finally, a DTI reconstruction (H) illustrates the integrity of white matter tracts, specifically highlighting a disruption or breakage in the corpus callosum fibers. This series serves as a pedagogical tool for understanding the natural history of viral encephalitis, from acute inflammatory edema and secondary hemorrhage to long-term neuroanatomical degeneration.
This composite diagnostic image displays six axial brain MRI sequences (A-F) documenting a case of viral encephalitis, specifically Japanese Encephalitis. Panels A-E represent the acute phase, showing symmetric involvement of the deep gray matter structures. (A) T1-weighted image reveals subtle hypointensity in the bilateral thalami, head of the caudate nuclei, and right lenticular nucleus. (B) T2-weighted imaging demonstrates corresponding hyperintensity in these regions, including the hippocampi. (C) Diffusion-weighted imaging (DWI) and (D) Apparent Diffusion Coefficient (ADC) map show bilateral punctate hyperintensity on DWI with corresponding hypointensity on ADC, indicating restricted diffusion and cytotoxic edema. (E) T2-FLAIR imaging confirms hyperintensity in the bilateral thalami and caudate heads without mass effect. (F) A follow-up T2-FLAIR image from two months later shows complete resolution of the previously seen signal abnormalities. The symmetrical involvement of the thalami and basal ganglia is a hallmark radiological finding for Flavivirus infections. This sequence serves as an educational example of deep gray matter restricted diffusion and its longitudinal progression in neuro-infectious diseases.
This set of four axial brain MRI images demonstrates diagnostic findings in a patient with anti-LGI1 encephalitis. (A) T2-weighted imaging (T2WI) and (C) T2-FLAIR sequences show hyperintense signals and mild cortical swelling within the right temporal lobe, right insular lobe, and right hippocampus. The left hippocampus appears normal on these sequences. (B) Diffusion-weighted imaging (DWI) reveals slightly elevated signal intensity in the corresponding right-sided regions. (D) Arterial Spin Labeling (ASL) perfusion imaging highlights significant focal hyperperfusion (indicated by the red/warm colors on the perfusion map) in the right temporal lobe, insula, and thalamus compared to the contralateral hemisphere. These combined radiological features—medial temporal lobe hyperintensity, hippocampus involvement, and regional hyperperfusion—are characteristic imaging markers for autoimmune encephalitis affecting the limbic system.
Japanese Encephalitis - Laboratory Diagnosis
1. Specimen Collection
| Specimen | Purpose |
|---|---|
| CSF | IgM ELISA (first-line), RT-PCR, virus isolation |
| Serum (acute + convalescent) | IgM ELISA; 4-fold IgG rise |
| Blood | RT-PCR in early/acute phase only |
2. CSF Findings (Lumbar Puncture)
- WBC: 10-500 cells/μL (rarely up to 1,000); early PMN predominance, shifting to lymphocytic predominance later
- Protein: Elevated, 50-100 mg/dL
- Glucose: Normal
- CSF findings are non-specific but consistent with viral/aseptic meningoencephalitis
3. Serological Tests (PRIMARY DIAGNOSIS)
A. IgM Antibody Capture ELISA (MAC-ELISA) - First-Line Test
- Recommended by WHO as the first-line rapid diagnostic assay
- Detects JEV-specific IgM in CSF or serum
- IgM appears in CSF by ~4 days after symptom onset; in serum by ~7 days after onset; some sources state as early as 3 days post-symptom onset
- Sensitivity in CSF: 65-70% (commercial assays)
- Specificity: 89-100% in CSF
- Available at commercial reference laboratories; confirmatory testing at CDC
- Limitation: Cross-reacts with other flaviviruses (dengue, West Nile, Zika, yellow fever) - confirmatory testing required
B. Plaque Reduction Neutralization Test (PRNT) - Gold Standard for Confirmation
- Gold standard for flavivirus diagnosis
- Distinguishes JEV-specific antibodies from cross-reacting flaviviral antibodies
- Used when MAC-ELISA is positive or equivocal, or where dengue co-circulation is a concern
- Not widely available; typically performed at reference/CDC laboratories
C. IgG Antibody (Convalescent Serology)
- A 4-fold rise in IgG titer between acute and convalescent serum samples is confirmatory
- Used when PRNT is unavailable
- Requires paired samples (acute + 2-4 weeks later), limiting early diagnosis
4. Molecular Tests
RT-PCR
- Detects JEV RNA in blood or CSF during early/acute phase (first few days of illness)
- Virus is replaced by antibody response rapidly, making PCR insensitive once neurological symptoms are established
- Low viral load means NAAT/RT-PCR should NOT be used to rule out infection in immune-competent patients
- Virus isolation from blood is infrequent; however, JEV can be isolated from CSF in up to 1/3 of patients with severe disease
5. Summary of Diagnostic Methods
| Method | Specimen | Sensitivity | Specificity | Timing | Notes |
|---|---|---|---|---|---|
| MAC-ELISA (IgM) | CSF/Serum | 65-70% (CSF) | 89-100% | From day 3-7 of symptoms | First-line; WHO recommended |
| PRNT | Serum | High | Very high | Convalescent | Gold standard; confirmatory |
| 4-fold IgG rise | Paired serum | Moderate | Moderate | Acute + convalescent | Alternative when PRNT unavailable |
| RT-PCR | Blood/CSF | Low (late disease) | High | First 1-5 days | Useful only in viremic phase |
| Virus isolation | CSF | ~30% (severe cases) | High | Acute | Reference labs only |
6. Neuroimaging (Supportive Diagnosis)
- T2/FLAIR hyperintense signal bilaterally in thalamus (most characteristic)
- Also: midbrain, basal ganglia, cerebellum
- Represents subcortical encephalitis
7. Differential Diagnosis Considerations
- Dengue virus
- West Nile virus
- Zika virus
- Yellow fever virus
- St. Louis encephalitis virus
Key Points
- Viremia resolves early - do not rely on culture or PCR in established disease
- IgM ELISA of CSF/serum is the standard first-line test (WHO recommendation)
- PRNT is the gold standard for confirmation and flavivirus differentiation
- CSF typically shows lymphocytic pleocytosis with normal glucose
- MRI thalamic T2 hyperintensity is the characteristic imaging finding
- JEV can occasionally be isolated from CSF in up to 1/3 of severe cases