Varicella-Zoster Virus (VZV) Workup

Updated: Feb 15, 2019
  • Author: Wayne E Anderson, DO, FAHS, FAAN; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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Laboratory Studies

When the presentation includes the typical dermatomal rash, additional studies are not required.

If the diagnosis is in doubt, a Tzanck smear can be performed and has a sensitivity of about 60%. To obtain a Tzanck smear, remove the crust from a vesicle and scrape the underlying moist skin with a No. 15 surgical blade. Smear the cells from the vesicle base onto a slide, fix for 1 minute with absolute alcohol, and stain with Wright stain (other staining methods can also be used).

The diagnosis can also be confirmed with a culture of vesicular fluid that is positive for varicella-zoster virus (VZV).

In cases of zoster sine herpete, DNA analysis via polymerase chain reaction (PCR) can be used for early diagnosis if laboratory turnaround time is reasonably short. If not, the decision of whether to start empiric acyclovir must be based on clinical grounds alone.

In cases of acyclovir-resistant VZV, detections of mutations in thymidine kinase can be determined by PCR and sequence analysis. Acyclovir-resistance may occur in stem cell transplant recipients. [5]


Imaging Studies

MRI may be useful if myelitis or encephalitis is suspected.



Lumbar puncture may be helpful if signs suggest myelitis or encephalitis. The cerebrospinal fluid (CSF) shows increased levels of protein and pleocytosis because the inflammatory response involves the leptomeninges. CSF PCR can be used to detect VZV DNA.

Although seldom necessary, biopsy results provide a definitive diagnosis.


Histologic Findings

The varicella zoster virus is a DNA virus with a genome that encodes 70 proteins.

The Tzanck preparation shows characteristic findings of giant cells with 2-15 nuclei. Recently infected epithelial cells contain a single enlarged nucleus with a thick nuclear membrane.

After reactivation, meningeal biopsy samples show a local inflammatory response, consisting of plasma cells and lymphocytes, that encompasses the leptomeninges.

Evidence has shown that motor neuron involvement is demyelinating rather than axonal.