Vesiculobullous Lesions
The Tzanck smear has been used since the 1940s to differentiate between etiologies of blistering disorders and is now most commonly used for the quick identification of herpetic lesions.1 The test is performed by scraping the base of a deroofed vesicle, pustule, or bulla, and smearing the cellular materials onto a glass slide. The most commonly utilized media for staining in the outpatient setting at my institution (University of Texas Dell Medical School, Austin) is Giemsa, which is composed of azure II–eosin, glycerin, and methanol. It stains nuclei a reddish blue to pink and the cytoplasm blue.10 After being applied to the slide, the cells are allowed to air-dry for 5 to 10 minutes, and Giemsa stain is subsequently applied and allowed to incubate for 15 minutes, then rinsed carefully with water and directly examined.
Other stains that can be used to perform the Tzanck smear include commercial preparations that may be more accessible in the inpatient settings such as the Wright-Giemsa, Quik-Dip, and Diff-Quick.1,10
Examination of a Tzanck smear from a herpetic lesion will yield acantholytic, enlarged keratinocytes up to twice their usual size (referred to as ballooning degeneration), and multinucleation. In addition, molding of the nuclei to each other within the multinucleated cells and margination of the nuclear chromatin may be appreciated (Figure 2). Intranuclear inclusion bodies, also known as Cowdry type A bodies, can be seen that are nearly the size of red blood cells but are rare to find, with only 10% of specimens exhibiting this finding in a prospective review of 299 patients with herpetic vesiculobullous lesions.11 Evaluation of the contents of blisters caused by bullous pemphigoid and erythema toxicum neonatorum may yield high densities of eosinophils with normal keratinocyte morphology (Figure 3). Other blistering eruptions such as pemphigus vulgaris and bullous drug eruptions also have characteristic findings.1,2
Gout Preparation
Gout is a systemic disease caused by uric acid accumulation that can present with joint pain and white to red nodules on digits, joints, and ears (known as tophi). Material may be expressed from tophi and examined immediately by polarized light microscopy to confirm the diagnosis.5 Specimens will demonstrate needle-shaped, negatively birefringent monosodium urate crystals on polarized light microscopy (Figure 4). An ordinary light microscope can be converted for such use with the lenses of inexpensive polarized sunglasses, placing one lens between the light source and specimen and the other lens between the examiner’s eye and the specimen.12
Parasitic Infections
Two common parasitic infections identified in outpatient dermatology clinics are scabies mites and Demodex mites. Human scabies is extremely pruritic and caused by infestation with Sarcoptes scabiei var hominis; the typical presentation in an adult is erythematous and crusted papules, linear burrows, and vesiculopustules, especially of the interdigital spaces, wrists, axillae, umbilicus, and genital region.1,13 Demodicidosis presents with papules and pustules on the face, usually in a patient with background rosacea and diffuse erythema.1,5,14
If either of these conditions are suspected, mineral oil should be used to prepare the slide because it will maintain viability of the organisms, which are visualized better in motion. Adult scabies mites are roughly 10 times larger than keratinocytes, measuring approximately 250 to 450 µm in length with 8 legs.13 Eggs also may be visualized within the cellular debris and typically are 100 to 150 µm in size and ovoid in shape. Of note, polariscopic examination may be a useful adjunct for evaluation of scabies because scabetic spines and scybala (or fecal material) are polarizable.15
Two types of Demodex mites typically are found in the skin: Demodex folliculorum, which are similarly sized to scabies mites with a more oblong body and occur most commonly in mature hair follicles (eg, eyelashes), and Demodex brevis, which are about half the size (150–200 µm) and live in the sebaceous glands of vellus hairs (Figure 5).14 Both of these mites have 8 legs, similar to the scabies mite.