Neurology, G.B. Pant Hospital, New Delhi, India.
Abstracts of the papers presented at the International Conference of Indian Virological Society on “Emerging and Re-emerging viral Diseases of the Tropics and Subtropics” at Indian Agricultural Research Institute, New Delhi, India, December 11–14, 2007.
Advancement in newer diagnostic modalities has helped in early diagnosis of viral encephalitis. Lymphocytic predominance in CSF is hallmark of viral encephalitis with normal protein and sugar. Currently available specific laboratory tests only help provide a retrospective diagnosis. Serologic tests depend on the occurrence of a rise in antibody titer. However, the early detection of specific immunoglobulin M (IgM) antibody may assist early diagnosis. Polymerase chain reaction (PCR) is a widely used method for early diagnosis of Herpes simplex virus (HSV) encephalitis. Compared with brain biopsy, the sensitivity of (HSV-1) PCR in encephalitis is better than 95% and the specificity approaches 100%. PCR has been found to detect Japanese encephalitis(JE) virus rapidly, being able to identify the virus within 2 days, as opposed to antibody detection, which may take weeks. PCR for rapid detection of West Nile virus in CSF has been developed. CT findings are usually not helpful in differentiating the different viral encephalitides. However, given the low cost and ready availability in most institutions, CT scan can readily reveal important complications, such as hemorrhage, hydrocephalus, and herniation, and can help guide neurosurgical interventions. MRI is more sensitive than CT scan in identifying viral encephalitides. In HSV encephalitis, MRI typically shows temporal lobe lesions, which may be hemorrhagic and unilateral or bilateral. MRI may help in differentiating Japanese B encephalitis from Nipah virus encephalitis. Japanese B encephalitis is characterized by gray matter involvement. Nipah virus encephalitis is associated with multiple, small, white matter lesions. The rhombencephalitis caused by enterovirus 71 can be visualized by T2-weighted MRI, which shows hyperintense signals in the brainstem. Magnetic resonance spectroscopy might be used in a similar way. PLEDS on EEG in HSVE is diagnostic but in other encephalitis focal or generalized slowing is most frequent finding. Brain biopsy is a vital tool in difficult and nonspecific encephalitis.
