Tzanck cells are observed under a microscope in fluid or scrapings from skin lesions like blisters or erosions. In dermatology, they serve as a rapid diagnostic indicator for certain skin conditions. Their presence guides healthcare professionals toward a preliminary diagnosis before more definitive tests are completed. The Tzanck test is a simple, low-cost, and quick procedure performed in a clinical setting.
Characteristics of Tzanck Cells
Tzanck cells originate from epidermal keratinocytes, the main cell type in the skin’s outermost layer. These cells acquire their distinct appearance due to acantholysis, the loss of cohesion between epidermal cells. This separation occurs when desmosomes, structures that link keratinocytes together, are disrupted.
When examined under a microscope, Tzanck cells are large and rounded, unlike the usual polygonal shape of healthy keratinocytes. They often contain multiple nuclei, appearing as multinucleated giant cells, a hallmark feature in certain viral infections. The nuclei themselves can be hypertrophic, with hazy or absent nucleoli and displaced chromatin pushed to the periphery of the nucleus, creating a “ground glass” appearance.
The cytoplasm of Tzanck cells is abundant and stains basophilic, often showing a deeper staining at the cell’s periphery, creating a “mourning-edged” appearance or a perinuclear halo. This characteristic morphology, including the multinucleation and altered nuclear features, is a direct result of viral replication within the cells, causing cellular changes and subsequent loss of intercellular adhesion.
The Tzanck Smear Procedure
The healthcare professional begins by selecting a fresh, intact skin lesion, as older, crusted lesions may yield fewer diagnostic cells. The top of the blister is carefully unroofed, or any crust is removed, to expose the base of the lesion.
A sterile scalpel blade or the blunt edge of a spatula is then used to gently scrape the base of the lesion and, in some cases, the underside of the blister roof. The collected material is then carefully transferred onto a clean glass slide. This is done by gently touching or smearing the scraping tool onto the slide to ensure cell adherence.
The prepared slide is then allowed to air dry, or it may be immediately fixed in alcohol if a Papanicolaou stain will be used. Following fixation, various stains can be applied, with Giemsa stain being one of the most common. Other stains like methylene blue, Wright’s stain, or Leishman stain can also be used.
After staining, the slide is rinsed with water and allowed to dry before being examined under a microscope, typically using an oil immersion lens for detailed cellular visualization. The entire process, from collection to microscopic examination, is quick, often providing results within minutes, making it a valuable bedside diagnostic tool.
Diagnostic Significance of Tzanck Cells
The presence of Tzanck cells on a smear is significant for rapidly identifying specific skin conditions. They are most commonly associated with viral infections caused by the herpes simplex virus (HSV) and varicella-zoster virus (VZV), which cause conditions like oral or genital herpes, chickenpox, and shingles. In these viral infections, the Tzanck smear reveals multinucleated giant cells and acantholytic cells, characteristic of viral cytopathic effects.
While primarily associated with herpes group viral infections, Tzanck cells can also be found in other less common dermatological conditions. For instance, they are observed in autoimmune blistering diseases such as pemphigus vulgaris.
Additionally, Tzanck cells may be seen in genetic conditions like Hailey-Hailey disease and Darier’s disease, both involving defects in cell adhesion. Although the Tzanck smear is not a definitive diagnostic tool for all conditions and may require confirmation with other tests like histology or viral culture, its ability to provide rapid, preliminary insights is beneficial, allowing for prompt initiation of appropriate treatment.