Dermpath pearls: Getting the most out of your biopsy submissions

March 12, 2021
Rebecca A. Packer, MS, DVM, DACVIM (Neurology/Neurosurgery)

Dr. Packer is an associate professor of neurology/neurosurgery at Colorado State University College of Veterinary Medicine and Biomedical Sciences in Fort Collins, and is board certified in neurology by the American College of Veterinary Internal Medicine. She is active in clinical and didactic training of veterinary students and residents and has developed a comparative neuro-oncology research program at Colorado State University.

dvm360, dvm360 April 2021, Volume 54,

Pathology is a collaborative process between clinicians and pathologists. Use these tips to increase the likelihood of ascertaining a definitive diagnosis for your patients with skin concerns.

Have you ever been frustrated when a pathology report from a skin biopsy is not as helpful or definitive as you hoped? Karen Trainor, DVM, MS, DACVP, owner of Innovative Vet Path in Leawood, Kansas, equates the biopsy evaluation to a microscopic physical examination. And to get the most information from a physical exam, a thorough and accurate history and knowledge of patient signalment must be gathered first. This helps the pathologist formulate a prioritized differential diagnosis, which is important because there is considerable overlap in the histopathologic appearance of certain diseases, and this ancillary information contributes to the pathologist’s ability to differentiate between diseases with similar pathologic appearances.

During a lecture at the recent Fetch dvm360® virtual conference, Trainor offered an in-depth look at how to get the most out of biopsy submissions. She discussed the role of a detailed history, the types of lesions encountered, and biopsy techniques and strategies to acquire the most diagnostic sample.

Gathering the patient history

Key points that are pertinent with regard to patient history include any systemic signs of illness, such as fever or malaise. Additionally, it is important to describe lesion distribution: whether lesions are symmetrical; whether lesion distribution is diffuse, generalized, focal, multifocal, regional, localized, or patchy; and whether there is a seasonal component to the clinical signs. It is also important to note whether dark or light pigmented areas are affected preferentially, and whether any changes in coat color have occurred. Additional details include standard descriptors such as size, shape, color, consistency, and texture. Photographs of the lesions provide a visual to accompany these descriptions and are essential to help correlate the histopathology findings with the clinical appearance and increase confidence in the diagnosis or ranking of differentials.

Another important element of the patient history is whether pruritis is present. Trainor noted that pruritis can be tricky to assess, as not all animals exhibit frank scratching behavior. In some cases, this manifests as rubbing, chewing, or licking. In the case of cats, excessive grooming may be the only sign of pruritis, and to make things more difficult cats often perform this grooming in secret. Other clinical elements of importance to share with your dermatopathologist include any previous treatments as well as the response to those treatments (no response, partial response, or worsening). These details can be very helpful to the dermatopathologist (Figures 1 and 2).

Much like any examination, it is always helpful to know what your client’s goals are and what they hope to accomplish or learn from the visit. In this case, however, the client is you, and the exam is the biopsy evaluation. It is assumed that the goal is a diagnosis, but if there are any specific questions you wish to have answered or specific differentials ruled in or out, be sure to include those on your submission form so the dermatopathologist can address them in their report.

When and how to biopsy

Trainor offered suggestions for relevant and complete submission information, as well as advice for determining when skin biopsies are appropriate and collection techniques that best preserve important pathological characteristics. In many dermatology cases, these are critical to arriving at a definitive diagnosis.

Indications and timing

Biopsies are indicated for persistent ulcerations, vesicular dermatitis, overt or suspected neoplasia, or when lesions are only partially responding to treatment or not responding at all. At least 3 to 5 biopsy samples should be submitted in an attempt to get various stages of lesion maturity, with a focus on sampling pustules, vesicles, and crusts. Ideally, label each sample regarding its specific location and lesion type.

The timing of biopsy is also important, given that some treatments can interfere with pathologic findings. Treatments such as shampoos, corticosteroids (topical, oral, or injectable), cyclosporine, antihistamines, antibiotics, and nonsteroidal anti-inflammatory drugs all have various washout periods, typically ranging from 1 to 6 weeks (Table). Although it is not always possible to accommodate washout periods in the real world, it is important to be aware of them, and to inform your dermatopathologist if any of these medications have been administered and when the last dose was prior to biopsy collection. This will allow them to interpret the lesions in the most appropriate context.

Collecting the biopsy

When preparing for the biopsy, avoid scrubbing any crusts on the skin because this is where key histopathologic features are often found, particularly in suspected cases of pemphigus foliaceus. Take care to preserve crusts when the prep includes trimming of hair as well. When sampling skin with hypotrichosis or alopecia, proper orientation of the biopsy specimen is critical. To aid the lab with optimum orientation during histologic process, Trainor recommends drawing a line on the skin using a Sharpie to denote the normal direction of hair growth prior to collecting the biopsies.

During biopsy collection, avoid pinching the specimen with forceps to prevent crush artifact as this can impede interpretation. Judicious use of electrocautery is recommended because it can cause significant coagulation artifact at the margins of skin biopsies, particularly for small samples or where measured margins are needed for neoplastic lesions (Figure 3). Similarly, where tissue cultures are submitted, Trainor noted that preservatives used in lidocaine from local blocks can inhibit growth of some bacteria, so use ring blocks in lieu of direct blocks in these circumstances.

The preferred collection technique depends on lesion type. Excisional biopsies are best for mass removal. Lesions of suspected vasculitis or lymphangitis require deeper tissue sampling than a typical punch biopsy can provide, so consider a deeper wedge or double punch technique. Elliptical techniques are most effective for biopsy of ulcers or bullae, and should include the edge of the lesion. A shave technique is commonly used on the nasal planum of cats with suspected squamous cell carcinoma. A shave technique also may be optimal for collecting intact pustules on the inner surface of the pinna because it helps to keep the pustule intact without causing damage to the underlying cartilage plate.

When using the punch biopsy technique, Trainor reiterated the importance of using a fresh biopsy punch and rotating the punch in a single direction (clockwise or counterclockwise) rather than oscillating back and forth. Other than biopsies obtained near the eye, pinnae, nasal planum, or foot pad of small dogs and cats (in which a 4-mm punch may be most feasible), a 6- to 8-mm punch should be used to provide a sufficient number of follicles and enough surface area to be informative. Punch biopsies 2 mm in diameter are of negligible diagnostic value.

Location also matters. Trainor said that often it is the periphery of lesions that are most diagnostic, rather than the center, which may be more necrotic. It is the edge of ulcers that tend to include crusts (Figure 4). Other areas of focus would be samples that include the loss of cobblestone appearance of the nose, and areas of deep pigmentation where there is still some gray coloration. When sampling paw pads, the carpal pad is a good choice as it is non-weight bearing.

Shipping the sample

Trainor also presented some tips for shipping samples. When shipping in cold temperatures where freezing is a concern, add 1 part isopropyl alcohol to 9 parts 10% neutral buffered formalin to prevent freezing and its associated artifact. In some instances, freeze-artifact can render a sample uninterpretable.

Collaboration is key

Be sure to reach out to your dermatopathologist if you have any questions about how to best approach the biopsy procedure. Remember that this is a collaborative effort, and pathologists are there to support you and help you help your patients. Because dermatopathology is a fairly nuanced subspecialty, submitting samples to pathologists with a specific expertise in dermatopathology will be an asset, particularly in those cases where there is overlap in the histopathologic appearance of competing diagnostic differentials.

Karen Trainor, DVM, MS, DACVP, is a Dermpath Detective at Innovative Vet Path (innovativevetpath.com) who helps veterinarians and dermatologists around the world diagnose skin conditions in animals. She is a dermatopathology VIN consultant, teaches dermatopathology to clinical dermatology residents, enjoys lecturing about all things dermpath, and is the founder of the educational Facebook group Veterinary Derm Path Forum. Trainor can be reached at Hello@innovativevetpath.com or by calling 913-303-7717.

Rebecca A. Packer, DVM, MS, DACVIM (Neurology/Neurosurgery), is an associate professor at Colorado State University College of Veterinary Medicine and Biomedical Sciences in Fort Collins. She is active in clinical and didactic training of veterinary students and residents and has developed a comparative neuro-oncology research program at Colorado State University.

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