Bedside Diagnostics for the Dermatologist: Pearls, Pitfalls, Practical Uses

Dr. Karolyn Wanat presented information about microscopy techniques dermatologists can perform at bedside. She used patient cases to demonstrate the utility of these techniques in a variety of settings and noted the similarities among features seen on microscopy and histopathology. Although histopathology may still be needed to confirm the diagnosis, direct microscopy can enable earlier diagnosis and treatment and differentiate between benign and life-threatening infections in acute care settings (e.g., newborn infants, immunosuppressed patients).

First, Wanat shared techniques for collecting samples from lesions. Tzanck smears are a rapid diagnostic test used to identify cutaneous infections (i.e., herpetic viruses) and blistering diseases. Dermatologists should consider the pathophysiology of the suspected disease to determine which areas of a lesion to scrape. Smear contents should be applied to one side of a glass slide (one with frosted header is best), from one side to the other. Inflammatory cells can be visualized in the thickest part of the smear; cytologic features are easiest to identify in the thinnest part.

For infections caused by parasites or mites such as scabies, dermatologists should collect specimens from burrows or papules by scraping vigorously to reach the stratum corneum. Dipping the blade in mineral oil or saline to soften the stratum corneum to help with acquisition of material and combining scraping with dermoscopy increases the yield. In cases of suspected scabies, dermoscopy allows for the visualization of the delta wing sign that identifies the mite’s location. The vinyl adhesive test can be used to identify scabies and systemic fungal infections. The burrow ink test can be used to identify scabies and Demodex mites.

Often, collected specimens are prepared for staining by air fixation, where the smear dries on the slide. Air fixation can cause keratinocyte ballooning and may lead to misdiagnosis when using Tzanck smears to diagnose acantholytic disorders (i.e., Grover’s disease). Misdiagnosis can be prevented with alcohol fixation by submerging the specimen in alcohol or squeezing a bedside alcohol wipe over the specimen.

Second, Wanat described the best practices for staining and visualizing samples under the microscope. Any staining technique can be used as long as the dermatologist knows the staining characteristics. Quik-Dip staining develops faster than Wright-Giemsa but expires after 30 days. Papanicolaou staining turns epithelial cells orange. Potassium hydroxide (KOH) staining is used to visualize fungal infections. Chlorazol black is a chitin-specific fungal stain that contains KOH and dimethylsulfoxide (DMSO). Specimens stained with KOH should be heated before visualizing to break down keratinocytes; specimens stained with chlorazol black do not need to be heated because DMSO breaks down keratinocytes. If the diagnosis is uncertain, multiple lesions can be scraped and the contents smeared on both sides of the slide, staining one side with Wright-Giemsa or Quik-Dip and the other with KOH or chlorazol black.

When visualizing specimens under the microscope, condenser placement is critical and will be dependent on the microscope. The condenser should be moved to the highest location to improve resolution for Tzanck smears and to the lowest location to enhance contrast for KOH and chlorazol black staining.

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