Tzanck smear

What is a Tzanck smear?

The Tzanck smear test is a simple and cheap test that relies on viewing and interpretation of single cells (cytology).

Arnault Tzanck described the technique in 1947 to distinguish various blistering conditions.

The test is not often performed, due to the development of histology, virological culture, polymerase chain reaction (PCR) and electron microscopy.¹

Indications for Tzanck smear

The Tzanck smear is mainly used in an acute setting to rapidly detect a herpes infection or to distinguish Stevens- Johnson syndrome / toxic epidermal necrolysis (SJS/TEN) from staphylococcal scalded skin syndrome. However, it can be used to diagnose a variety cutaneous infections and blistering diseases.

How is a Tzanck smear prepared?

Select a fresh blister on the patient.

• Using a blunt scalpel blade, gently deroof the lesion
• Scrape the base of the lesion
• Smear the tissue onto a clean microscope slide
• Allow it to dry in the air
• Fix the specimen with preservative

Deroof blister

Smear onto slide

Air dry

Add fixative

What happens in the laboratory?

The slide is stained. The choice of stain depends on the sample and diagnostic possibilities.

Giemsa stain

Giemsa stain is poured over the slide. After 15 minutes, the slide is washed with sterile water.

• Cell cytoplasm stains blue
• Nuclei stain purple/red/pinkish

Toluidine blue

Toluidine blue is more rapid than Giemsa, as it only requires staining for 60 seconds.²

Tzanck smear interpretation

Characteristic cytological findings of Tzanck smears follow.³

Cutaneous infections

• Bacterial infections
  • Bullous impetigo: dyskeratosis, acantholytic cells, clusters of cocci, abundant neutrophils
  • Staphylococcal scalded skin syndrome: dyskeratosis, acantholytic cells, no or little inflammation, cocci, absence of abundant neutrophils
• Viral infections
  • Herpes simplex and herpes zoster: Ballooning multinucleated giant cells and eosinophilic inclusion bodies
  • Viral warts: koilocytes
  • Molluscum contagiosum: intracytoplasmic inclusion bodies ("Henderson-Patterson's bodies")
  • Hand foot and mouth disease: syncytial nuclei, absence of acantholytic cells
• Fungal infections
  • Candidiasis: pseudohyphae and spores
  • Histoplasmosis
  • Cryptococcosis
  • Sporotrichosis: spherical, oval or cigar-shaped yeasts and asteroid bodies
• Parasites
  • Scabies: Sarcoptes scabiei (4 pairs of legs and multiple dorsal cuticular spines)
  • Leishmaniasis: ellipsoid-shaped Leishman-Donovan bodies, Wright's cells

Blistering diseases

• Pustular disease of the newborn: exclude infection, neutrophils observed in toxic erythema of the newborn
• Pemphigus vulgaris: acantholytic cells
• Stevens- Johnson syndrome / toxic epidermal necrolysis (SJS/TEN: necrotic basal cells, leukocytes, fibroblasts

Cutaneous neoplasms

• Melanoma: atypical melanocytes
• Basal cell carcinoma: clusters of basaloid cells.
• Seborrhoeic keratosis: hyperkeratosis, horny cysts

The Tzanck smear test was found to have similar diagnostic accuracy to dermatoscopy in pigmented skin lesions.⁴

Inflammatory skin diseases

• Allergic contact dermatitis: tadpole cells, lymphoctyes
• Irritant contact dermatitis: tadpole cells, polymorphonuclear leukocytes
• Necrobiosis lipoidica: palisading granuloma, necrobiotic material
• Foreign body granuloma: foreign body

Advantages and disadvantages of Tzanck smear test

Initial results from a Tzanck smear should normally be confirmed by other techniques, such as biopsy or PCR.

Advantages

Tzanck smear has the following benefits:

• It is inexpensive
• It results in minimal discomfort to patients
• It is quick: useful for initial evaluation, or when rapid diagnosis required or in recurrences of disease. Faster diagnosis leads to early initiation of treatment.

Disadvantages

Tzanck smear requires expertise:

• In preparing the slide
• In interpreting cytology

False negatives may occur in early or late disease.