Which procedures may be helpful in the diagnosis of herpes simplex virus (HSV) infection?

Updated: Feb 27, 2019
  • Author: J Michael Klatte, MD; Chief Editor: Russell W Steele, MD  more...
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Answer

The Tzanck preparation can be used for the cytologic identification of vesicular exanthems caused by herpesviruses. In the event of a positive test, the microscopist cannot differentiate between infections caused by HSV-1, HSV-2, and varicella zoster virus, however.An intact vesicle is aspirated with a sterile tuberculin syringe. This fluid may be submitted for viral isolation. After the vesicle is aseptically unroofed, the base of the lesion is vigorously scraped with a scalpel or a wooden applicator. The resultant material is placed on a slide, air dried, fixed, and stained, usually with Giemsa or Wright stain.

A positive result is denoted by identification of typical multinucleated giant cells or, uncommonly, Cowdry type A intranuclear inclusion bodies. If the examiner is experienced, 40-80% of culture-positive specimens are recognized as positive by cytologic examination. Appropriate immunofluorescent antibody reagents facilitate the identification of different herpesviruses and some viruses other than herpesviruses.

Lumbar puncture (LP) with submission of CSF for the Gram staining, bacterial culture, and other analyses (eg, determination of cell counts, protein, and glucose levels) is essential when patients with encephalitis are evaluated. Hemorrhagic CSF may be found in herpes simplex virus encephalitis. LP is contraindicated in patients with marked increased intracranial pressure.

All patients with neonatal CNS herpes simplex virus infection should undergo repeat LP at the end of intravenous (IV) acyclovir therapy to determine that the CSF specimen is negative for herpes simplex virus on PCR testing by a reliable laboratory and to document end-of-therapy CSF indices. [10]

Historically, brain biopsy results were frequently used to diagnose herpes simplex virus CNS disease and to exclude other potential pathologic processes. PCR is currently the standard diagnostic modality for herpes simplex virus CNS disease. However, if multiple PCR results are negative in a patient who has signs and symptoms strongly suspicious for herpes simplex virus encephalitis, brain biopsy may be contemplated. It is important to note that CSF PCR testing results in patients with HSV encephalitis can be falsely negative when obtained prior to the third day of illness. [18]


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