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
What happens in the laboratory?
The slide is stained. The choice of stain depends on the sample and diagnostic possibilities.
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 is more rapid, as it only requires staining for 60 seconds.2
Tzanck smear interpretation
Characteristic cytological findings of Tzanck smears follow.3
- Bacterial infections
- Viral infections
- Fungal infections
- 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
- 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.
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.
Tzanck smear requires expertise:
- In preparing the slide
- In interpreting cytology
False negatives may occur in early or late disease.