p.1

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

p.2

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

p.3

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

p.4

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

p.5

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

p.6

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

p.7

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

p.8

If necessary, clip the hair

p.9

Slide, mineral oil, #10 scalpel blade

p.10

Touch the blade to the oil

p.11

Pinch the skin

p.12

For demodicosis, capillary oozing

p.13

For scabies, sample the stratum corneum

p.14

For scabies, sample the stratum corneum

p.15

Wipe the material onto the slide

p.16

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

p.17

Use of clear acetate tape to collect parasites

p.18

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

p.19

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

p.20

Rub the slide on the skin

p.21

Even between the digits

p.22

Or the bottom of the foot

p.23

Sample the ear canal with a cotton - tipped swab

p.24

DiffQuick stain (no need to heat fix)

p.25

Malassezia pachydermatis (OIF)

p.26

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

p.27

Cytology of pustule – neutrophils, intracellular cocci

p.28

Pemphigus foliaceus

p.29

Acantholytic cells – pemphigus
10X
Tzank prep

p.30

4. Wood’s lamp / Ultraviolet light

p.31

4. Wood’s lamp / Ultraviolet light

p.32

Fluorescent positive hairs, M. canis

p.33

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

p.34

Pluck fluorescent positive hairs

p.35

Scrape broken hairs and scales

p.36

Sterile / clean toothbrushes

p.37

Brush non - lesional animals, 5 minutes

p.38

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

p.39

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

p.40

Dermatophytosis – Diagnosis
Saprophyte (contaminant)

p.41

Microsporum canis

p.42

Trichophyton mentagrophytes

p.43

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

p.44

Clear acetate tape

p.45

Tape attached to a stick

p.46

Ribbon of new methylene blue

p.47

Collecting spores on the tape

p.48

Place the tape on the stain

p.49

Microsporum canis , macroconidia

p.50

Microsporum canis , macroconidia

p.51

Microsporum canis , macroconidia
More than 6 divisions

p.52

Trichophyton mentagrophytes , microconidia, spiral hyphae

p.53

Microsporum gypseum , macroconidia

p.54

Microsporum gypseum , macroconidia

6 or fewer divisions

p.55

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

p.56

Intact pustule to be sampled

p.57

Culturette tube

p.58

Gently cleanse the top of the pustule

p.59

Open the pustule with a new 25 ga needle

p.60

Pustule contents wiped onto the culture swab

p.61

Culture swab into the transport media

p.62

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

p.63

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

p.64

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

p.65

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

p.66

Biopsy punch

p.67

Area to biopsy

p.68

Biopsy site marked

p.69

Injecting local anesthetic

p.70

Injecting local anesthetic, close up
Bleb

p.71

Using a biopsy punch

p.72

Using a biopsy punch, close up

p.73

Removal of the punch

p.74

Removal of the sample

p.75

Skin post biopsy

p.76

Sample submission

p.77

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

p.78

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

p.79

Intradermal test for atopy – syringes

p.80

Intradermal test for atopy – shaved

p.81

Intradermal test for atopy – marked

p.82

Intradermal test for atopy – injecting

p.83

Intradermal test for atopy – completed

p.84

Intradermal test for atopy – indirect light

p.85

Intradermal test – weak positive reactor

p.86

Intradermal test – weak positive reactor, close up

p.87

Intradermal test

p.88

Intradermal test

p.89

Intradermal test – indirect light

p.90

Intradermal test – black dog

p.91

Intradermal test – flea antigen

p.92

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

p.93

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

Courtesy of Dr. Peter Hill

p.94

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

p.95

Color Dilution Alopecia

p.96

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

p.97

Trichography – color dilution alopecia

p.98

Trichography of fluorescing hair
Arthroconidia
Courtesy of Dr. Tim Nuttall

p.99

Fungal arthrospores

p.100

DIAGNOSTIC TECHNIQUE

p.101

QUESTIONS ???