Which other dermatologic or infectious conditions, besides molluscum contagiosum, can be identified using a Tzanck smear?

Tzanck Smear Applications Beyond Molluscum Contagiosum

The Tzanck smear is primarily used to diagnose herpes simplex virus and varicella-zoster virus infections by identifying multinucleated giant cells, and additionally serves as a rapid diagnostic tool for pemphigus group disorders by detecting acantholytic cells. 1

Primary Indications for Tzanck Smear

Herpesvirus Infections (Most Common Use)

• Herpes simplex virus (HSV) and herpes zoster (varicella-zoster virus) are the classic indications, with the presence of multinucleated giant cells being diagnostic for herpesvirus infection 1
• The sensitivity exceeds 80% and specificity reaches 90% when performed by experienced operators on vesicular lesions 2
• Multinucleated giant cells have a sensitivity of 84.7% for herpetic infections 3
• Critical limitation: The Tzanck smear cannot differentiate between HSV and varicella-zoster virus—speciation requires immunofluorescence antigen testing, culture, or PCR of vesicle fluid 1

Varicella (Chickenpox)

• Varicella presents with vesicular lesions that demonstrate the same multinucleated giant cells as herpes zoster, making Tzanck smear particularly useful in vesicular stage diagnosis 2
• The test is especially valuable in newborns and immunocompromised patients with vesicular dermatoses 2

Secondary Diagnostic Applications

Pemphigus Group (Autoimmune Bullous Diseases)

• Acantholytic cells are the hallmark finding in pemphigus disorders, with sensitivity of 80.70-85.0% and specificity of 68.18-87.50% 4, 5
• Both complete and incomplete acantholytic cells are diagnostic—incomplete cells (60.32% of cases) can help identify pemphigus even when classical features are absent 4
• Rounding and nuclear enlargement are the most consistent features of acantholytic cells 4

Bullous Impetigo (Bacterial Infection)

• Dyskeratotic acantholytic cells combined with cocci have 100% sensitivity for bullous impetigo 3
• Gram staining can be added to the Tzanck preparation to identify bacterial organisms 3

Candidiasis

• Pseudohyphae on Tzanck smear have 100% sensitivity for cutaneous candidiasis 3
• This finding can rapidly confirm fungal infection when clinical suspicion exists 3

Spongiotic Dermatitis

• More than 10 tadpole cells (at 100x magnification) have 81.5% sensitivity for spongiotic dermatitis 3
• This represents an underutilized application of the Tzanck smear 3

Algorithmic Approach to Tzanck Smear Interpretation

If Multinucleated Giant Cells Are Present:

• Diagnose herpesvirus infection (HSV or varicella-zoster) 1, 2
• Obtain vesicle fluid for immunofluorescence, culture, or PCR to differentiate HSV from varicella-zoster 1
• This distinction is critical for infection control and antiviral dosing decisions 1

If Acantholytic Cells Are Present:

• Consider pemphigus group disorders first 3, 4
• Look for complete versus incomplete acantholytic cells—both are diagnostic 4
• Pitfall: Acantholytic cells can also appear in spongiotic dermatitis and genodermatoses, requiring clinical correlation 6
• Dyskeratotic keratinocytes in vacuolar interface dermatitis may be difficult to distinguish from acantholytic cells 6

If Dyskeratotic Acantholytic Cells Plus Cocci Are Present:

• Diagnose bullous impetigo 3
• Consider Gram staining for bacterial confirmation 3

If Pseudohyphae Are Present:

• Diagnose cutaneous candidiasis 3

If More Than 10 Tadpole Cells Are Present (100x magnification):

• Consider spongiotic dermatitis 3

Critical Pitfalls to Avoid

• Do not rely on Tzanck smear alone to differentiate HSV from varicella-zoster—this distinction requires additional testing and has significant treatment implications 1
• Timing is critical: The Tzanck smear is most reliable when obtained from vesicular stage lesions; sensitivity drops significantly in crusted or ulcerated lesions 2
• Acantholytic cells are not specific to pemphigus—they can appear in spongiotic dermatitis, genodermatoses, and vacuolar interface dermatitis 6
• Operator experience matters significantly: Sensitivity and specificity depend heavily on the skill of the person performing and interpreting the smear 2, 3
• A negative Tzanck smear does not exclude disease—cytology never replaces culturing or histopathology for definitive diagnosis 2

When to Perform Tzanck Smear

• First-line investigation for any vesicular, pustular, erosive, or bullous skin lesion where rapid diagnosis would alter immediate management 6, 5
• Particularly valuable in immunocompromised patients and newborns with vesicular dermatoses 2
• Most useful when performed at bedside for immediate clinical decision-making before culture or biopsy results are available 3, 5