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Maximizing the use of dermatopathology
In patients with unusual, severe, or nonresponsive dermatologic lesions, histopathology can be an important test to obtain a definitive diagnosis and guide treatment.
Dermatology cases are a common presentation to the general practitioner. Although a vast number of patients have an underlying allergic condition that may present with a secondary pyoderma, other pathology can occur in the skin, including autoimmune diseases, genetic disease, and neoplasia. When cytology, skin scrape, trichogram, and culture have not yielded a diagnosis, biopsy should be considered.
Joya Griffin, DVM, DACVD, of the Animal Dermatology Clinic in Louisville, Kentucky, and star of the Nat Geo Wild television series Pop Goes the Vet With Dr. Joya, discussed tips for maximizing the use of histopathology in dermatology cases during a session at dvm360®’s 2022 Atlantic Coast Veterinary Conference in Atlantic City, New Jersey.
When to consider histopathology
Skin histopathology allows the veterinarian to “know what we are treating, [determine] how to treat it, and let pet parents know what to expect,” said Griffin. Reasons to consider histopathology include cases where lesions are unusual in appearance or distribution, neoplasia is suspected, resolution is not seen with clinically appropriate management, or to obtain a definitive diagnosis prior to starting treatment that carries significant side effects.
Prior to performing histopathology, all patients should have a full dermatologic database performed, including skin scraping, cytology, and skin cultures, if indicated. Secondary infections should be addressed with antibiotic therapy and may require several weeks of treatment prior to biopsy. Ideally, corticosteroid therapy should be withdrawn prior to biopsy, Griffin noted.
Maximizing the yield of histopathology
Griffin reminded clinicians that a typical dermatopathology report will contain a morphologic diagnosis and a list of differential diagnoses. The final diagnosis can be achieved by combining this information with clinical history, lesion distribution, and lesion appearance. Griffin recommends establishing a relationship with a skilled dermatopathologist to maximize results. She noted that sending a detailed clinical history—including previous therapy and responses, a lesion map, and photographs—can be extremely helpful for the pathologist. “[The pathologist] only sees 6 mm of tissue. We are seeing the whole dog,” said Griffin.
Multiple samples should be submitted that are representative of all types of lesions on the patient. “Lesions have lives,” said Griffin. For example, a pustule becomes a crust, which becomes a collarette. Submitting a sample from each type of lesion provides maximal information. Griffin noted that many veterinarians are taught to sample at the edge of the lesion, but she only recommends this in cases of ulcerated lesions, where the center of the lesion may be necrotic and offer no helpful information. In most cases, “your pathologist doesn’t need normal [skin],” said Griffin. When possible, submitting a lesion in its entirety is preferred, especially in cases of solid nodules and small lesions.
Some types of disease processes require special considerations when selecting sample sites. In cases of depigmentation, samples should be collected from gray areas or the margin between pigmented and nonpigmented areas. For patients with alopecia, samples should be collected from fully alopecic areas, areas of thinning haircoat, and areas of normal haircoat to capture the entire disease process.
Tips for sample collection
Histopathology samples can often be obtained under sedation with local anesthesia, though patients with large lesions or abnormalities in sensitive areas such as the paw pads or mucocutaneous junctions may benefit from general anesthesia. Griffin reminded veterinarians that skin biopsies are not sterile. The area should not be surgically prepped as close clipping and scrubbing can result in loss of important information on the skin surface. Hair in the areas of sampling can be trimmed with scissors or a #40 clipper blade.
Samples should be handled gently and placed in formalin quickly to avoid creating artifact. The punch biopsy instrument should only be rotated in one direction with even pressure. Griffin noted that the sample should be handled gently from the base to avoid crushing. Cautery should be avoided. Samples are also at risk of freezing if shipped over a longer period, such as the weekend, in cold temperatures, so timing of submissions can be important.
Finally, Griffin recommended taking large samples. Six- to 8-mm punch biopsies are preferred except in areas prone to scarring or that are difficult to close, such as paw pads and pinnae. Elliptical and wedge biopsies can also be considered, especially in lesions that are deep or fragile.
Ultimately, dermatopathology results are maximized when veterinarians “sample multiple sites, take big samples, and find a dermatopathologist [they] can trust,” said Griffin.
Griffin J. Beyond skin deep: utilizing histopathology as part of your dermatologic work up. Presented at: Atlantic Coast Veterinary Conference; October 10-12, 2022: Atlantic City, NJ.
Kate Boatright, VMD, is a 2013 graduate of the University of Pennsylvania, a practicing veterinarian, a freelance speaker, and an author in western Pennsylvania. She is passionate about mentorship, education, and addressing common sources of stress for veterinary teams and recent graduates. Outside of clinical practice, Boatright is actively involved in organized veterinary medicine at the local, state, and national levels.
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