Dermatologic clinical pathology for dummies

This content is sponsored by Truview.

Digital imaging and artificial intelligence (AI) are rapidly growing factors in veterinary medicine. Dermatologic cases are the most common nonvaccine presenting complaints to small animal veterinarians based on the latest pet insurance–based study.

Dermatology is a visual science. To make an accurate diagnosis and to get the best possible treatment outcome, you will need to use all your senses. But your eyes will be the most important of all. Sometimes they will not be enough to gather all the information you need.

A good quality microscope will be necessary for the successful practice of dermatology. It should be binocular with a variety of objectives. A new option recently developed is the digital microscope, which can help document lesions for owners and medical records. The author is using Zomedica’s Truview digital microscope in his dermatology practice. Unlike other digital scopes, Truview can use an unstained slide and perform all the staining and preparation for you, thus freeing technicians to accomplish other tasks. The stained images are then scanned and available to be viewed on the screen and via the internet at MyZomedica.com. These digital images can be shared with a clinical pathologist for expedient results/ second opinion. New platforms are also available to interface AI with this clinical data for rapid, accurate results.

Image courtesy of Truview.

Superficial and deep skin scrapings are commonly performed in clinical cases, especially those with alopecia and folliculitis. The skin is squeezed and then abraded with a mineral oil–coated dull scalpel blade or skin spatula. The skin should show evidence of capillary oozing when complete. The sample is placed on a glass slide and viewed on ×4/power. It may be easier to view mites if the condenser is lowered slightly. For cases of demodicosis, the author likes to record mite counts, percentage of live vs dead mites, and percentages of the various life stages. Evidence of a single sarcoptic mange mite or egg is all that is needed to diagnose sarcoptic mange. Hair plucks may be substituted for skin scrapes, especially in difficult areas to scrape, such as the interdigital spaces.

Cytology of the skin and ear is helpful in clinical dermatology cases. Skin cytology samples are obtained either by direct smear or clear tape preparation. Be certain never to use frosted tape. The author frequently uses tape impressions on dry, scaly lesions and impression smears on moist lesions. Staining the samples with Diff-Quik or Wright-Giemsa stain kit is the most used in North America. Heat-fixing the slide prior to staining is up to the individual’s preference. Evaluation for the presence of bacteria and yeast is then done using 4×100 magnification. The morphology of the bacteria and whether they are intracellular or extracellular should be noted. The most common bacteria seen are cocci Staphylococcus, Streptococcus, and rods such as Escherichia coli and Pseudomonas. Malassezia spp, with their characteristic bowling pin shapes, should be evaluated for numbers per field.

Tzanck preparations (named for French hematologist Arnault Tzanck, MD) are cytology of material aspirated from an intact pustule or from under a moist crust. They are helpful in diagnosing pemphigus diseases with their hyper-segmented neutrophils devoid of bacteria and positive for acantholytic cells.

TRUFORMA can accurately check canine and feline thyroxine, free thyroxine, thyrotropin, and canine cortisol and corticotropin (ACTH) levels.

Bacterial cultures and dermatophyte cultures must be properly implemented when working up difficult clinical dermatology cases. Dermatophyte cultures can be routinely done in-house. Dermatophytes preferentially metabolize protein in the culture medium and their alkaline metabolites turn the media red. Scale and hair plucks are inoculated into the media. A sterile toothbrush can be used to comb an entire cat (especially a suspected carrier) to obtain samples. The colonies are usually white or tan when mature. Identification of the species is recommended using lactophenol cotton blue stain to look at the macroconidia/ microconidia of the fungal species. The author recommends sending fungal cultures to a reference laboratory for more accurate diagnosis and speciation. The newer polymerase chain reaction (PCR) panel detects Microsporum and Trichophyton with greater than 95% sensitivity and 99% specificity, respectively. A positive PCR test can be the result of active infection, fomite carriage, or nonviable fungal organisms from a successfully treated infection.¹

In clinic hematology, serum chemistry and urinalysis are now commonly utilized in small animal practices. Dermatologic cases may show changes seen with analyzers including anemia of chronic disease, eosinophilia, hypoalbuminemia, hyperglobulinemia, and proteinuria. Many cases will have elevated alanine aminotransferase/alkaline phosphatase levels with many medications, especially corticosteroids.

An exciting new addition to small animal practice is Zomedica’s Truforma for point-of-care endocrine assays. Truforma can accurately check canine and feline thyroxine, free thyroxine, thyrotropin, and canine cortisol and corticotropin (ACTH) levels. This can be especially helpful in differentiating between sick euthyroid syndrome and hypothyroidism in canine patients. This is the first analyzer that will provide accurate, in-house measurement of canine ACTH levels. This is an excellent screening test for hyperadrenocorticism that can be accomplished in less than 1 hour.

There is an art and science of taking good samples for dermatopathology. It is always preferable to take non-traumatized primary lesions such as papules and pustules. Always try to give the dermatopathologist more than one sample. The sample should never be scrubbed prior to biopsy, and always grasp the biopsy plug from the base to avoid crushing artifacts.

Proper use of your clinical laboratory is essential for the accurate diagnosis and treatment of canine and feline dermatoses. Many new diagnostic tools have become available in recent years that can aid in your efforts to make the pet and owner happy and healthy.

Reference

Moriello KA, Coyner K, Paterson S, Mignon B. Diagnosis and treatment of dermatophytosis in dogs and cats.: Clinical Consensus Guidelines of the World Association for Veterinary Dermatology. Vet Dermatol. 2017;28(3):266- e68. doi:10.1111/vde.12440

Robert O. Schick, DVM, DACVD, has practiced veterinary dermatology since 1986 and he became the first board-certified veterinary dermatologist in Atlanta, Georgia. Schick completed both his bachelor’s degree and DVM at the University of Florida. He completed a small animal internship at Oradell Animal Hospital and his residency at The University of Pennsylvania. Schick has practiced in multiple locations recognizing the extreme needs of dermatologic care across the country. He began serving the needs of the Florida panhandle in 2015. Schick, who is also a commercial pilot, volunteers his time with the Veteran’s Airlift Command to help transport military personnel in times of special need. Schick is very passionate about Gator Sports and loves to scuba dive in his spare time, taking special interest in under water photography.