Herpes simplex encephalitis is diagnosed by
A. MRIB. Biopsy
C. Corneal scrapping and culture
D. EEG periodic lateralised
E. CSF PCR of HSV DNA
Ans.
E. CSF PCR for HSV DNA :
• HSV
DNA polymerase chain reaction (PCR) in CSF is a rapid and sensitive and specific tool for early diagnosis and
rapidly replacing brain biopsy as the diagnostic standard.
According to Harrison it is the diagnostic procedure of choice with sensitivity
(98%) and specificity (94%), equal or exceed brain biopsy. PCR
results are not generally affected with1
wk of antiviral therapy.
• Brain biopsy:The isolation of HSV from brain tissue obtained at biopsy
was once “gold standard” for diagnosis of HSV encephalitis although with advent
of CSF PCR tests for HSV,itis no
longer necessary to perform biopsy. Tissue is cultured for virus and examined
histopathologically and ultrastructurally.
•MRI, CT, ECG: Less sensitive than HSV DNA PCR. Approx 10% and 33% of
PCR documented cases have normal MRI and CT respectively. CT is less sensitive
than MRI. EEG abnormalities
occur in >90% of PCR documented cases. HSV encephalitis show focal
findings
(i) Areas of increased signal intensity in frontotemporal, cingulate or insular
regions of brain on T2 weighted spino-echo MRI images.
(ii) Temporoparietal areas of low absorption, mass effect and contrast
enhancement on CT.
(iii) Periodic focal temporal lobe spikes on a back ground of slow or low
amplitude activity (flattened) on LEG. BEG finding is non specific.
• CSF shows lymphocytic pleocytosis, mildly elevated protein, normal glucose,
CSF culture for HSV-I encephalitis is invariably negative.
• Serologic studies and antibodies detection : CSF HSV antibodies and
antigen detection are done after 1 week of illness and who are CSF FCR negative
for HSV. They are of limited value in 1st week of illness.
