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Dermatologic diagnostics: What you can do in clinic (Proceedings)

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Apr 01, 2009

Parasitology

Deep skin scrape: Identifies Demodex mites. Clip hair from area, apply a thin film of mineral oil to site, squeeze skin to extrude mites, scrape area with a dull number 10 scalpel blade or a skin spatula, collect material on blade and transfer to a microscope slide, repeat scraping until capillary bleeding is noted (or your scrape is not deep enough). Make sure you have enough mineral oil on the slide, apply coverslip, then systematically examine area under cover slip for the presence of mites (note life stage- adult versus larva versus nymph versus egg, note if adults are alive or dead). Lower the condenser to increase contrast. Examine on 10X at low light.

Superficial skin scrape: Identifies Demodex mites that live in/on superficial skin layers (Demodex gatoi in cats, short Demodex mite of dogs- may be called Demodex cornei), Sarcoptes scabiei, Notoedres, Otodectes cynotis, Cheyletiella spp., lice, Lynxacarus radovsky (cat fur mite), etc.

Clip hair if needed from a large area, apply a thin film of mineral oil to skin surface, scrape skin surface with a dull number 10 scalpel blade or skin spatula, collect all material and transfer to a microscope slide. Scrape multiple large areas.

Hair plucks for mites: Identifies Demodex mites. Select site, gently grasp base of hairs with hemostats and pull in direction of hair growth, place hairs in mineral oil on slide, place coverslip on slide, and examine under 10X. Mites may be seen at base of hairs in keratin debris.

Tape preps for mites: Identifies skin surface dwelling Demodex mites and other superficial mites (Sarcoptes scabiei, Notoedres cati, Otodectes cynotis, Cheyletiella spp., lice, Lynxacarus radovsky, etc.) Use a small piece of clear packing tape to collect skin surface debris and hairs from multiple sites on the animal. Put a drop of mineral oil on slide, place tape on slide sticky surface down, and examine under 10X.

Ear swabs for mites: Identifies Otodectes cynotis and Demodex mites. Collect debris from ear canal on cotton swab and roll onto slide with a small amount of mineral oil, apply coverslip and examine under 10X.

Fecal flotation: Occasionally identifies Demodex gatoi in cats- they ingest the mites while grooming themselves.

Hand lens examination: can identify lice and Cheyletiella

Flea combing: best way to find fleas and/or flea dirt!

Cytology

Cytology is done primarily to identify infectious organisms, in particular bacteria (cocci versus rods) and yeast (Malassezia).

Tape impressions: Tear off a small piece of clear packing tape (we use 3M super strength mailing tape). Firmly press tape onto affected area and remove, repeating process until the tape is no longer sticky. Attach one end of tape to the bottom edge of a microscope slide and dip the tape into the three solutions that make up diff-quick stain, rinse tape, detach from bottom edge of slide, then place tape sticky surface down onto slide surface, blot on paper towel to dry, then examine microscopically. Tape impressions are good for drier areas or crevices (skin folds, interdigital area). Do not heat fix tape.

Slide impressions: Press slide surface directly onto skin to collect exudates, debris, etc. Good for easily accessible surfaces with moist exudates. Let dry, stain with diff-quick, then examine.

Sticky slide impressions: These are slides that come with a thin layer of adhesive on one side of the slide. Press the sticky side of the slide to the skin surface, diff quick, then examine. Good for drier areas, but difficult to get into crevices.

Superficial skin scrape: If there is a significant amount of greasy surface debris or purulent exudate, this material can be collected with a dull scalpel blade or skin spatula and smeared onto a slide. Heat fix if desired, stain with diff-quick, then examine.

Pustule cytology: Identifies infectious agents (bacteria), inflammatory cells (neutrophils, eosinophils, lymphocytes, macrophages), acantholytic cells (seen most often with Pemphigus foliaceus). Open the surface of the pustule with a 25 gauge needle (held close to parallel with the pustule surface), then either press a slide to the pustule contents or collect the pustule contents with the needle and smear contents on the slide. Stain with diff-quick, then examine. If pustules are not present, but crusts are, do impression smears of the crusts and the raw skin/exudates underneath them.

Ear cytology: Identifies infectious organisms, inflammatory cells, occasionally neoplastic cells. Collect exudates fro canals with a cotton swab, roll onto a slide, heat fix if desired, stain with diff-quick, then examine.