Tzanck Smear and Diagnostic Cytology
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Direct answer
The Tzanck smear is a rapid bedside cytology test in which cells scraped from the base of a fresh vesicle are stained and examined for multinucleate giant cells. It detects herpes simplex and varicella-zoster infection, and it also shows acantholytic cells in pemphigus. The test is quick and cheap, but it cannot tell herpes simplex from varicella-zoster, so viral PCR is needed for a definite result.
What you must remember
- Specimen: cells scraped from the base of a fresh, unroofed vesicle or bulla, not from a crusted lesion.
- Stains: Giemsa or Wright stain after fixing the smear in methanol.
- Multinucleate giant cells: the classic finding in herpes simplex and varicella-zoster infection, reflecting viral cytopathic change.
- Acantholytic cells: rounded keratinocytes with large nuclei, seen in pemphigus vulgaris and also called Tzanck cells in that setting.
- Limit: the smear cannot distinguish herpes simplex from varicella-zoster.
- Sensitivity: lower than viral PCR or direct immunofluorescence, so a negative smear does not exclude herpes.
- Confirmation: viral PCR of vesicle fluid or scrapings is preferred for a definite diagnosis of herpes simplex or varicella-zoster.
- Non-specificity: acantholysis also occurs in Hailey-Hailey disease and Darier disease, so the smear alone does not diagnose pemphigus.
A stepwise method from vesicle to report
A Tzanck smear is only as good as the sample, so the choice of lesion and the scraping technique matter as much as the stain. Follow the steps in order and send the slide for review when the result is unclear.
- Select a fresh lesion: choose a tense, recently formed vesicle or bulla, since older lesions yield few cells.
- Unroof the lesion: remove the roof with a scalpel blade or forceps to expose the base.
- Scrape the base: scrape the floor of the lesion firmly enough to obtain cells without causing bleeding.
- Smear and air-dry: spread the material thinly on a clean glass slide and allow it to dry.
- Fix and stain: fix in methanol and stain with Giemsa or Wright stain, then examine under the microscope.
- Interpret and confirm: report multinucleate giant cells or acantholytic cells, and send vesicle fluid or scrapings for PCR when an infection needs to be confirmed.
A positive smear points to herpes group infection or pemphigus, but the pattern alone does not identify the virus. Histopathology and immunofluorescence are needed when pemphigus is suspected, because the smear cannot separate pemphigus from other acantholytic diseases.
Where the Tzanck smear catches candidates
The smear looks simple, and examiners use its limitations to set traps.
- Trap: treating a positive Tzanck smear as proof of herpes simplex Correct: multinucleate giant cells appear in both herpes simplex and varicella-zoster, so type-specific PCR is needed.
- Trap: assuming a negative Tzanck smear excludes herpes Correct: sensitivity is limited, so a clinically suspected infection still needs PCR or culture.
- Trap: scraping a crusted, old lesion Correct: sample a fresh vesicle, since crusts and old lesions contain few usable cells.
- Trap: treating acantholytic cells as specific to pemphigus Correct: acantholysis also occurs in Hailey-Hailey disease and Darier disease, so it is not diagnostic alone.
Frequently asked questions
What cells does a Tzanck smear show in herpes simplex infection?
A Tzanck smear in herpes simplex infection shows multinucleate giant cells, which result from the viral cytopathic effect on keratinocytes. The same finding occurs in varicella-zoster, so the smear confirms a herpes group infection rather than a specific virus.
Can a Tzanck smear distinguish herpes simplex from varicella-zoster?
A Tzanck smear cannot distinguish herpes simplex from varicella-zoster, because both produce multinucleate giant cells. Viral PCR or direct immunofluorescence of vesicle material is needed to identify the virus.
What are Tzanck cells in pemphigus vulgaris?
Tzanck cells in pemphigus vulgaris are rounded acantholytic keratinocytes with large nuclei, seen when vesicle material is smeared and stained. They reflect loss of intercellular adhesion, and histopathology is used to confirm the diagnosis of pemphigus.
Which stain is used for a Tzanck smear?
A Tzanck smear is usually stained with Giemsa or Wright stain after the smear has been fixed in methanol. These stains highlight the nuclear features of multinucleate giant cells and acantholytic cells, which are the diagnostic findings.
Why is PCR preferred over a Tzanck smear for herpes?
PCR is preferred over a Tzanck smear for herpes because it is more sensitive and specific, and it identifies the virus type. A Tzanck smear is quick and inexpensive but cannot separate herpes simplex from varicella-zoster or detect a low viral load reliably.