Page 267 - WSAVA2017
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C. Pucheu-Haston1
1Louisiana State University School of Veterinary Medicine, Veterinary Clinical Sciences, Baton Rouge, USA
CM Pucheu-Haston, DVM, PhD, DACVD
Department of Veterinary Clinical Sciences, School of Veterinary Medicine
Louisiana State University, Baton Rouge, LA, USA
Tip #3:
Know how to select sites for biopsy. Some clinical lesions are more likely to yield diagnostic samples than other ones. As a general rule, primary lesions (plaques, pustules, vesicles, nodules and the edges of eroded or ulcerated lesions) tend to yield better diagnostic results. In contrast, biopsies of lichenified skin, excoriated skin, scars and the center of ulcers are unlikely to provide useful information.
Tip #4:
Don’t be afraid to take multiple biopsies. There are
a number of dermatologic conditions in which the “diagnostic lesion” can be very difficult to find. The likelihood of finding this diagnostic lesion increases
with every sample provided. It increases even more when the samples represent a spectrum of the disease process, including older lesions (or the center of lesions), developing lesions (or the edge of spreading lesions) and sometimes even “normal skin” immediately adjacent to the affected area. Similarly, the biopsy must include the affected area. If the lesion to be sampled appears to
be subcutaneous in location (as might be the case for some tumors or panniculitis / cellulitis cases), samples that only include the overlying skin may not include the information that the pathologist needs. In this case, an excisional wedge biopsy may be appropriate. Alternately, deep tissue can sometimes be sampled by first taking an 8mm punch biopsy, then a 6mm biopsy punch taken through the primary biopsy site. Inform the pathologist if this technique is used.
Tip #5:
Know how to prepare for a biopsy. As a general rule, less disruption is better. If the area to be biopsied is
in haired skin, the hair should be carefully clipped no shorter than 4-8mm in length to avoid disturbing surface scales and crusts. The skin to be biopsied should NOT be scrubbed or soaked in antiseptic unless the biopsy
is to be used only for culture. The area should be blocked by subcutaneous (not intradermal) injection of lidocaine, with or without bicarbonate. In some cases, it may be preferable to perform a line or ring block a few centimeters away from the site itself. Examples where this would be appropriate include biopsies to be taken for culture (the preservative in the lidocaine may kill microbes) or lesions that appear to extend to the deep dermis or subcutis. Topical application of anesthetic creams may cause distortion of the epidermis and should be avoided.
An Urban Experience
  Skin biopsies can provide the skilled clinician with a detailed image of the pathologic processes occurring in diseased skin. Unfortunately, all too often the clinician receives a histologic description and interpretation that may not be clinically helpful. While bad biopsies can certainly happen to good clinicians, there are a few techniques that you can use to maximize the likelihood of obtaining a diagnostic sample.
Tip #1:
Understand what you can and cannot reasonably expect from a biopsy. Unfortunately, many dermatologic conditions do not have a pathognomonic histologic appearance. For example, most hypersensitivity disorders can be impossible to distinguish histologically. In these cases, a biopsy will be useful to distinguish
a possible hypersensitivity from a non-allergic cause
of pruritus (e.g., infection, neoplasia), but cannot be expected to identify the specific hypersensitivity involved (e.g., food allergy).
Tip #2:
Know when to biopsy. Biopsies are most useful when secondary infections and self-trauma are resolved. Often, clients delay in presenting a pet for veterinary care until
the problem becomes almost unbearable. As a result,
the underlying problem is often overwhelmed or masked by damage/scarring due to self-trauma or by secondary infections with bacteria and/or yeast. It is often prudent
to initiate antibiotic / antifungal therapy and place the patient in a restraining cone to prevent self-trauma for 1-2 weeks prior to taking the biopsy. Whenever possible, anti- inflammatory medication (such as glucocorticoids) should be avoided for a couple of weeks prior to a biopsy to avoid artifactual alteration of the histologic pattern.

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