Page 1454 - Clinical Small Animal Internal Medicine

1392 Section 12 Skin and Ear Diseases

microscopic evaluation at ×10 and then ×100 magnifica- magnification. When aberrant hairs are identified, they
VetBooks.ir tion. The evaluation of otic cytology is discussed in more can be examined more closely with ×40 magnification.
detail in Chapter 167.

In general, surface‐dwelling mites such as Sarcoptes,
Fine Needle Aspirate Skin Scrapes
Fine needle aspirates are best utilized for evaluation of Notoedres, Cheyletiella, D. cornei, and D. gatoi are best
nodular to tumorous lesions. A 20–25 gauge needle procured via superficial skin scrapes, whereas follicular
attached to a 6–12 cc syringe is used to aspirate the mites, including D. canis, D. cati, and D. injai, require
lesion. It is important to release the pressure on the deep skin scrapes for diagnosis.
syringe before the needle is withdrawn from the lesion. The superficial skin scrape is performed by applying
Once the needle and syringe are removed from the several drops of mineral oil onto the area to be scraped
lesion, the needle is detached and the plunger of or onto the chosen skin scraping tool. If necessary, the
the syringe is pulled back to draw air into the barrel. The overlying hair can be shortened with a No. 40 clipper
syringe is then reattached to the needle and the contents blade to facilitate the scraping procedure, but the clipper
are expressed onto a slide, gently smeared using a sepa- blade should not touch the skin surface or any lesions, if
rate clean slide and allowed to air‐dry. Alternatively, the present. A No. 10 scalpel blade is used to scrape a large,
fine needle capillary technique can be used. A 22–25 broad area approximately 10–15 times. Alternatively, a
gauge needle is introduced into the lesion by holding skin scraping spatula (Jorgensen Laboratories, Loveland,
onto the hub. Several quick, back‐and‐forth movements CO) can be used. Obtaining capillary bleeding is not
are then made in multiple directions within the lesion, necessary, as it is more important to scrape broad, large
without completely withdrawing the needle, to ensure a areas to increase the chances of procuring these difficult‐
representative sample is obtained. The needle is then to‐find surface‐dwelling mites. For scabies, preferred
withdrawn and attached to a syringe (6–12 cc) into which sampling sites include the margins of the pinnae, elbows,
air was already drawn. The plunger is then depressed to and tibiotarsal areas, as these are the most commonly
expel the material within the needle onto a clean glass afflicted sites, even if one only identifies mild, subtle
slide, spread, and allowed to air‐dry. lesions. Papules, if present, should also be scraped. The
Following the use of either technique, the slide is material is then transferred to a glass slide and a cover
then stained with Diff‐Quik. Other staining options slip is applied. The sample is then evaluated microscopi-
include gram stain or new methylene blue. Evaluation cally with either ×4 (scanning objective) or ×10 magnifi-
for microorganisms, such as bacteria, yeast and deep cation in a systematic fashion. The condenser should be
fungal species, and for the overall cell type (i.e., inflam- lowered to increase contrast and facilitate the finding of
matory or neoplastic) is performed by first evaluating mites. Look for all parasitic life stages. The observation
the specimen using the ×10 objective and finally with of just one egg is considered a positive finding; however,
the high‐power objective (×40). The oil immersion a negative skin scrape does not rule out surface mites. In
objective can also be utilized to evaluate the sample in these cases, when the aforementioned mites are sus-
greater detail. pected but cannot be confirmed with superficial skin
scrapings, a treatment trial may be needed to verify the
Trichography (Hair Examination) presence (or absence) of these mites (see Diagnostic
Trichography is used for a number of indications. It Treatment Trials below and see also Chapter 165).
can be used to detect the presence of parasitic or infec- Deep skin scrapes differ from the superficial version in
tious organisms, such as Demodex and dermatophyte that the sample will be procured from a focal, localized
arthrospores. Traumatic hair loss due to pruritic behav- area, squeezing the skin prior to the scrape (and during
iors can be confirmed by the presence of hair shafts with the scrape if possible) to facilitate extrusion of the mites
blunted tips. When hairs are predominantly found to be from the follicles. Several drops of mineral oil are applied
in telogen (i.e., resting phase), this may be an indication either directly to the sample area or to the No. 10 scalpel
that an underlying endocrinopathy or follicular arrest blade or skin scraping spatula and the skin is scraped in
may be present. Finally, a presumptive diagnosis of vari- the direction of hair growth until capillary bleeding is
ous follicular dysplasias can be made when, for example, evident. Lesions that should be scraped include areas
marked melanin clumping is present within the hair where comedones, erythema, scaling, papules, and pus-
shafts. The author prefers to gently pluck the hairs using tules are evident. The author finds that comedones are
the fingertips so as not to create iatrogenic trauma. The especially important lesions to scrape when follicular
hairs are then placed onto a slide with a drop of mineral demodicosis is suspected. The collected material is then
oil in an orderly array. A cover slip is placed atop the transferred to a glass slide and a cover slip applied and
sample and evaluation is initially performed using ×10 evaluated as described above. If properly performed with