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Diagnostic Techniques in Veterinary Dermatology

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Candace A. Sousa, DVM, Dipl. ABVP, Dipl. ACVD VetScope 2021-09-01

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Diagnostic Techniques in
Veterinary Dermatology

Candace A. Sousa, DVM
Diplomate (Emeritus) American Board of Veterinary Practitioners,
Canine and Feline Practice
Diplomate (Emeritus) American College of Veterinary Dermatology

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In-Clinic Dermatology Tests
Dermatology is easy as there are only 9 tests that we do
- 8 1⁄2 can be done by technicians, and we only need 2 power tools!
1. Skin scraping
‒ Superficial for S. scabiei, Notoedres, D. gatoi
‒ Deep for Demodex spp
2. Acetate tape preparation
‒ Cheyletiella
‒ Lice

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In-Clinic Dermatology Tests
3. Cytologic examination
‒ Pustule
‒ Surface debris
‒ Ears

4. Wood’s lamp examination
‒ M. canis; hairs

5. Fungal culture (DTM)

6. Bacterial culture +/- susceptibility

7. Skin biopsy

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In-Clinic Dermatology Tests
8. Intradermal test or allergen-specific IgE serology
‒ Fleas only
‒ Complete panel

9. Trichogram
‒ Blunted or chewed hairs
‒ Color dilute dogs
‒ Dermatophytes (?)
• CBC / chemistry profile (including T4) / UA / fecal

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Make a “Derm Box” for each exam room, treatment area and
include:
• No. 10 dull scalpel blades
• Spatula
• Mineral oil
• Flea comb
• Glass slides
• Double-sided tape
• Cotton swabs
• 25 gauge needles
• Culturettes
• Caliper/ ruler

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Skin Scraping
• Demodex canis
• Sarcoptes scabiei
• Notoedres cati
• Cheyletiella sp
• Other

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1. Skin Scraping

• Superficial for S. scabiei, Notoedres, D. gatoi
• Deep for Demodex spp

• All dogs and cats with alopecia
• All dogs and cats with comedones
• All dogs and cats with crusts
• All dogs and cats prior to the use of corticosteroids

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If necessary, clip the hair

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Slide, mineral oil, #10 scalpel blade

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Touch the blade to the oil

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Pinch the skin

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For demodicosis, capillary oozing

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For scabies, sample the stratum corneum

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For scabies, sample the stratum corneum

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Wipe the material onto the slide

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2. Acetate tape to collect “bugs”
• Cheyletiella
• Lice

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Use of clear acetate tape to collect parasites

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3. Cutaneous Cytology
• Should be performed in almost every case
‒ Pustule
‒ Surface debris
‒ Ears
‒ Draining tracts
• Identification of bacteria and yeast

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Cutaneous Cytology
• Various collection methods
‒ Direct touch prep
‒ Spatula
‒ Cotton-tipped swab
‒ Clear acetate tape
‒ Sticky slides
– DuraTak
– Double-sided tape

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Rub the slide on the skin

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Even between the digits

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Or the bottom of the foot

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Sample the ear canal with a cotton - tipped swab

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DiffQuick stain (no need to heat fix)

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Malassezia pachydermatis (OIF)

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Otic cytology
100X 100X
Bacteria - Cocci Bacteria - Rods

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Cytology of pustule – neutrophils, intracellular cocci

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Pemphigus foliaceus

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Acantholytic cells – pemphigus
10X
Tzank prep

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4. Wood’s lamp / Ultraviolet light

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4. Wood’s lamp / Ultraviolet light

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Fluorescent positive hairs, M. canis

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5. Fungal Culture
• Gently wipe or cleanse
• Collect fine scales and broken hairs
‒ Those that fluoresce
‒ Sterile toothbrush, about 30 strokes
• Material pressed onto, not into, the agar
• Room temperature or warmer
• Needs air
• Examine daily

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Pluck fluorescent positive hairs

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Scrape broken hairs and scales

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Sterile / clean toothbrushes

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Brush non - lesional animals, 5 minutes

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Fungal culture
• RED COLOR CHANGE WITH THE FIRST SIGN OF COLONY GROWTH
• Colonies are white or cream-colored
• Dermatophytes usually grow within 10 days
• Keep cultures for 21 days

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Derm - Duet; color change with the first sign of colony growth

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Dermatophytosis – Diagnosis
Saprophyte (contaminant)

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Microsporum canis

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Trichophyton mentagrophytes

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Identification of the colony
• Wet mount or acetate tape preparation
• Lactophenol cotton blue, new methylene blue or blue from the Diff- Quik stain

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Clear acetate tape

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Tape attached to a stick

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Ribbon of new methylene blue

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Collecting spores on the tape

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Place the tape on the stain

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Microsporum canis , macroconidia

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Microsporum canis , macroconidia

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Microsporum canis , macroconidia
More than 6 divisions

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Trichophyton mentagrophytes , microconidia, spiral hyphae

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Microsporum gypseum , macroconidia

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Microsporum gypseum , macroconidia

6 or fewer divisions

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6. Bacterial Culture and Susceptibility

• For those cases where a mixed population of bacteria is seen with cytology
• For those cases that don’t respond to empirical choice of an antibiotic
‒ Confirm it’s a bacterial infection
‒ Identify resistant bacteria
• For those cases where therapy may be have side effects, be difficult to administer, or be expensive

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Intact pustule to be sampled

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Culturette tube

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Gently cleanse the top of the pustule

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Open the pustule with a new 25 ga needle

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Pustule contents wiped onto the culture swab

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Culture swab into the transport media

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7. Skin Biopsy

• Cases that should be biopsied
‒ A patient who is systemically ill
‒ If there is no response to therapy within 3 weeks
‒ Any suspected neoplastic disorder
‒ If there is a persistent ulcer
‒ If the possible therapy will be expensive, dangerous, or time-consuming

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Anesthesia
• In most cases a local anesthesia can be used
‒ Epinephrine 1:1000 into the hub of the syringe
‒ Lidocaine 1 - 2% or bupivacaine 0.25
– 0.5%, 2.5ml
‒ Sodium bicarbonate 8.4%, 0.25ml
‒ Use a 25 gauge needle if possible
‒ 0.5 – 1.0 ml subcutaneously / site

• If the animal is intractable or you need to biopsy a sensitive area such as the nasal planum, mucous membrane, pinnae, or foot pad, can sedate or even use general anesthesia

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Biopsy sampling
• Mark sites with a permanent marker pen
• Minimum of 3 samples; 5 is ideal
• Shave hair if necessary but do not wash
• 6mm disposable punch biopsy; occasionally a 4mm punch
• Elliptical excision of an ulcer or vesicle

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Biopsy sampling
• Gentle removal of the sample
• Blot if necessary
• Site closed with a simple interrupted or cruciate suture

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Biopsy punch

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Area to biopsy

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Biopsy site marked

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Injecting local anesthetic

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Injecting local anesthetic, close up
Bleb

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Using a biopsy punch

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Using a biopsy punch, close up

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Removal of the punch

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Removal of the sample

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Skin post biopsy

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Sample submission

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What to do with the samples
• Preserve in 10% formalin
• Send the samples to a veterinary pathologist with experience with dermatohistopathology
• Best to request a microscopic description
• Give a good history or tentative diagnosis
• Suture removal in 7-10 days and discuss results with the owner

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8. Intradermal test
• A way to identify relevant allergens for immunotherapy after diagnosing atopic dermatitis
• A way to identify flea allergic dogs

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Intradermal test for atopy – syringes

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Intradermal test for atopy – shaved

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Intradermal test for atopy – marked

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Intradermal test for atopy – injecting

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Intradermal test for atopy – completed

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Intradermal test for atopy – indirect light

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Intradermal test – weak positive reactor

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Intradermal test – weak positive reactor, close up

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Intradermal test

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Intradermal test

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Intradermal test – indirect light

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Intradermal test – black dog

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Intradermal test – flea antigen

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9. Trichography
• Examination of hair roots
• Examination of hair tips
‒ Self-induced alopecia
• Examination of hair shaft
‒ Macromelanosomes in the cortex of color dilute hairs
‒ Fungal arthrospores

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Trichography (examination of hairs)
Fractured tip - chewing Tapered tip - normal

Courtesy of Dr. Peter Hill

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Telogen (resting) Anagen (growing)
40X PH VM PH
Courtesy of Drs. Peter Hill, William Miller

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Color Dilution Alopecia

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Trichography – color dilution alopecia
Clumped melanin / macromelanosome
40X
Courtesy of Dr. William Miller

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Trichography – color dilution alopecia

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Trichography of fluorescing hair
Arthroconidia
Courtesy of Dr. Tim Nuttall

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Fungal arthrospores

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DIAGNOSTIC TECHNIQUE

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QUESTIONS ???

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