What is the role of PCR in the diagnosis of herpes simplex encephalitis (HSE)?

Updated: Jul 17, 2018
  • Author: Wayne E Anderson, DO, FAHS, FAAN; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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Answer

CSF should be sent for HSV-1 and HSV-2 polymerase chain reaction (PCR) study. PCR analysis of CSF for the detection of HSV DNA has virtually replaced brain biopsy as the criterion standard for diagnosis. [7, 8] Schloss and colleagues report that whereas quantitative PCR is more rational than a nested PCR, the former has little prognostic use. [36]

PCR is highly sensitive (94-98%) and specific (98-100%). Results become positive within 24 hours of the onset of symptoms and remain positive for at least 5-7 days after the start of antiviral therapy.

Clinical severity and outcome appear to correlate with viral load as assessed by quantitative PCR techniques, [37] but not all investigators have confirmed this correlation. [38]

False-negative findings may occur early in the course of the disease when viral DNA levels are low (within 72 hours of the onset of symptoms) or when blood is present in the CSF, because hemoglobin may interfere with PCR. [39]

Pretest probability should be considered in interpretation of results. A negative result obtained less than 72 hours after the onset of symptoms in a patient with a high pretest probability (on the basis of fever, focal neurologic abnormalities, or CSF pleocytosis) should be repeated.

False-positive test results are rare and usually reflect accidental contamination of the specimen in the laboratory.


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