Varicella-Zoster Virus (VZV) Workup

Updated: Oct 01, 2021
  • Author: Zartash Zafar Khan, MD, FACP; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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Workup

Laboratory Studies

Confirmation methods for lab testing are the following:

PCR to detect VZV DNA from base of a deroofed vesicular lesion is the most reliable and sensitive method, and is now considered the gold standard. False-negative PCR results are more likely to occur from lesions in vaccinated persons.

Direct immunofluorescence (DFA) to detect VZV antigen is the second choice; sensitivity is only 60–70% of cases detectable by PCR.

Viral culture of VZV is possible but is insensitive, time-consuming and expensive because it requires special media.

Serologic tests may be used to confirm disease but are less reliable than PCR or DFA for virus identification. A fourfold or greater rise in serum varicella IgG titers from acute- and convalescent-phase samples indicates a recent VZV infection. However, persons in whom vaccination produced a high VZV IgG titer may not achieve the required fourfold increase in the convalescent sample. Serologic tests are also less useful in immunocompromised people who are less likely to mount an effective immune response. Testing for VZV IgM by using commercial kits is not recommended because available methods lack sensitivity and specificity. 

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Imaging Studies

MRI may be useful if myelitis or encephalitis is suspected.

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Procedures

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.

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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 two to 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.

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