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• Authors' reply
  Peter GE Kennedy
  Published on: 5 November 2002
• Does a positive HSV PCR neccesarily mean Herpes Simplex encephalitis?
  Dougall J.P McCorry
  Published on: 1 November 2002

• Published on: 5 November 2002

  Authors' reply

  • Peter GE Kennedy, Professor of Neurology
  • Other Contributors:
    • Abhijit Chaudhuri

  Dear Editor

  Dr McCorry makes an intriguing point that has indeed occurred to us before. It is theoretically possible that a positive PCR HSV result in the CSF could reflect asymptomatic HSV latency in the sensory ganglia and/or CNS and not viral reactivation causing encephalitis. However, it would be difficult to explain how the virus reaches the CSF from the ganglia or brain in the absence of reactivation. Also, i...

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  Dear Editor

  Dr McCorry makes an intriguing point that has indeed occurred to us before. It is theoretically possible that a positive PCR HSV result in the CSF could reflect asymptomatic HSV latency in the sensory ganglia and/or CNS and not viral reactivation causing encephalitis. However, it would be difficult to explain how the virus reaches the CSF from the ganglia or brain in the absence of reactivation. Also, in practical terms, the PCR test has been shown in several studies to have a very high specificity ie a very low false positive rate, this being based on testing of large numbers of CSF samples from individuals with conditions other than herpes simplex encephalitis. So in practice this possibility seems not to be a problem. In order to answer this question unequivocally it would be necessary to correlate CSF positivity or negativity for HSV with known ganglionic positivity. But this is not possible in practice since the demonstration of HSV latency in ganglia has been based on autopsy studies, such tissues not being accessible in live individuals.

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  Conflict of Interest:
  None declared.

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• Published on: 1 November 2002

  Does a positive HSV PCR neccesarily mean Herpes Simplex encephalitis?

  • Dougall J.P McCorry, Specialist Registrar Neurology

  Dear Editor

  The assumption is that if PCR for HSV in the CSF is positive this then confirms the diagnosis of Herpes Simplex Encephalitis, yet it is known that the HSV genome is found in 85-90% of patients at unselected necroscopy in the trigeminal ganglion and so do we know whether HSV DNA can be found in healthy individuals? Could it be that some positive PCR results are truely positive, and not due to con...

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  Dear Editor

  The assumption is that if PCR for HSV in the CSF is positive this then confirms the diagnosis of Herpes Simplex Encephalitis, yet it is known that the HSV genome is found in 85-90% of patients at unselected necroscopy in the trigeminal ganglion and so do we know whether HSV DNA can be found in healthy individuals? Could it be that some positive PCR results are truely positive, and not due to contamination, but do not reflect Herpes simplex encephalitis. If this were the case then PCR tests for patients with 'atypical' or 'mild' disease would carry a significant false positive rate.

  I would be interested in the author's thoughts.

  Dougall McCorry

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  Conflict of Interest:
  None declared.

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