Page 1457 - Clinical Small Animal Internal Medicine

157 Approach to the Patient with Dermatologic Disease 1395

a life‐threatening dermatosis, autoimmune or metabolic filled vials are readily available in a number of sizes and
VetBooks.ir disease, or the suspicion of neoplasia, biopsy should be volumes, respectively.
The biopsy sites must remain perfectly intact and be
immediately undertaken. Finally, skin biopsies are par-
ticularly indicated when a specific condition is suspected
and the histopathology is recognized to be diagnostic of handled carefully. A scissors or clippers can be used if
necessary to gently shorten the overlying hair and
that disease. Other less critical reasons for pursuing improve visualization of the area to be biopsied, taking
biopsy include when other tests have not resulted in extreme care not to touch the skin surface or disturb the
identification of the condition and when treatment has lesion itself, including crusts. Preliminary scrubbing
not resolved the problem. It is important to remember should never be performed, except in the case of dermal
that performing a skin biopsy is never useless. In the best or subcutaneous nodules, where a light prep with 70%
case scenario, it provides a definitive diagnosis, and in alcohol should suffice. An indelible marker is used to cir-
the worst case it can rule out other dermatoses and nar- cle the lesion and a local anesthetic, such as 2% lidocaine,
row down the category of diseases to be considered. is injected subcutaneously using a 25 gauge needle and
Inform the owner that a precise diagnosis may not be fanning it under the area of the circle. The needle is
reached but in any case the information obtained will be inserted at the periphery of the site to be biopsied so as
useful. not to disturb the lesion itself. Typically 0.5–2.0 mL of
In order to maximize results, biopsies must be taken anesthetic per site should suffice. The maximum dose of
that are representative of the entire disease process. This lidocaine that may be administered is 5 mg/kg in dogs
entails the procurement of spontaneous, primary lesions and 2.5 mg/kg in cats to avoid adverse effects, such as
which generally occur earlier in the course of the disease, cardiac arrhythmias. Wait at least five minutes prior to
along with secondary, more chronic lesions. Therefore, biopsy to allow for optimal analgesic effect.
in almost all cases, multiple biopsies should be taken in Center the lesion within the punch biopsy tool and
order to capture the clinical spectrum and evolution of choose a size that minimizes the amount of normal skin
the disease. It is prudent to select lesions that have not margin. However, for vesicles, bullae and pustules, which
been altered by scratching or infection. For depigment- are fragile and can easily rupture with biopsy, use the
ing diseases (e.g., discoid lupus erythematosus), newly largest punch possible or perform an excisional or wedge
depigmented areas are ideal sites for biopsy (e.g., the biopsy. If the procurement of subcutaneous fat is essen-
slate gray areas of the nasal planum rather than the more tial to establishing an underlying diagnosis, it may also
chronic white/pink or ulcerated areas). When ulcerated be pertinent to use an excisional or wedge biopsy tech-
areas need to be sampled, biopsy the advancing edge to nique, and anesthetize the area using a ring block to min-
include some of the epidermis rather than the center of imize distortion of the subcutaneous tissue due to local
the ulcer. For diseases characterized by alopecia, biopsies lidocaine infiltration. Rotate the punch biopsy tool in
should be obtained from the most chronic area of com- one direction to minimize damaging shearing forces and
plete alopecia as well as from the junctional and normal apply even, continuous pressure until an adequate depth
areas. has been obtained to free the tissue down to the subcuta-
If possible, glucocorticoid therapy should be discon- neous fat layer, which should be included in the speci-
tinued 2–3 weeks prior to biopsy. If a long‐acting inject- men as it may be important for the accurate assessment
able corticosteroid was administered to the patient, it is and diagnosis of many inflammatory processes. An edge
best to postpone the biopsy for 6–8 weeks, when feasi- of the subcutaneous fat is gently grasped using an atrau-
ble. Generally, 3–5 biopsies are an acceptable average. matic tissue forceps to elevate the specimen. The epider-
When possible, a 6 or 8 mm punch biopsy tool is used. A mis or dermis should not be grasped, as this could result
3 or 4 mm instrument is used only for difficult‐to‐biopsy in a crushing artifact and lead to a nondiagnostic sample.
areas (e.g., periocular region, pinnae, nasal planum or The subcutaneous attachment is then cut. The author
footpad). In many cases, punch biopsies can be per- prefers a straight or curved iris scissors in most cases.
formed using local anesthesia with 2% lidocaine, with or The biopsy sample is then gently blotted to remove
without sedation. However, when biopsying challenging excess artefactual blood from the surface.
areas, general anesthesia may be best. The sample should be immediately placed in 10% for-
It is helpful to create a small dermatology surgery pack malin, with a minimum of 10 parts formalin to 1 part
so that all necessary instruments and materials are tissue required for adequate fixation. Thin samples
readily available. Include a No. 10 scalpel blade and han- should be placed, panniculus down, on a small piece of
dle, straight and curved iris scissors, gauze, Mayo and tongue depressor before placement into the fixative to
Metzenbaum scissors, needle and suture, an atraumatic prevent rolling of the specimen, which can make histo-
forceps such as a Debakey tissue forceps, and a needle pathologic evaluation more challenging. Affixed sam-
holder. Disposable biopsy punches and 10% formalin‐ ples must be placed face down into the formalin jar. The