Herpes simplex encephalitis | PGI entrance Preparations

Herpes simplex encephalitis is diagnosed by 

A. MRI 
B. Biopsy 
C. Cornealscrapping 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.