diagnostic sampling

Question 1

when searching for mites, what power do you use on the microscope

Answer 1

4x

Question 2

where should you examine the hair for nits when looking for lice

Answer 2

hair shaft

Question 3

describe the process of using unstained acetate tape to search for surface mites

Answer 3

• tape is pressed over multiple sites of scaling and dragged across the hairshafts
• tape placed directly on slide with no oil or staining
• viewed on low lower (4x) with light beam diaphragm partially closed

Question 4

what is the difference in finding in a superficial skin scrape vs a deep skin scrap

q

Answer 4

superficial for surface parasites
deep for burrowing parasites as it sloughs off the epidermis

Question 5

discuss how to choose the best site for skin scraping

Answer 5

• scrape non-traunmatised primary lesions where possible
• if looking for sarcoptes: look for lesions on pinnal margin, elbows, hocks or ventrum
• if demodex: incude areas of alopecia, comedones, hyperpigmentation

Question 6

describe the process of taking a good quality skin scrape sample

Answer 6

• clip hair from samping area (do no disturb scale or skin surface if superficial)
• place mineral oil onto scalpel blade and a few drops directly onto skin
• squeeze skin prior to scraping if suspect demodex
• scrape with the balde at 90 degrees to the skin surface in the direction of hair growth
• if deep: scrape until starts to ooze blood. if superficial, no need to draw blood
• put material on 1 or more slides in mieral oil and cover with coverslip
• partially close light beam diaphargm on the microscope to improve contrast
• scan whole slide systematically using 4x or 10x objective

Question 7

name some common pitfalls of skin scrapings

Answer 7

• inadequate liquid parafin
• no coverslip
• light intensity too great
• too few scrapings (take at least 6 if possible)
• sample obscured by blood
• sample too thick

Question 8

describe the process of hair plucking to make trichograms

Answer 8

• pluck small group of hairs near base with fine forceps in direction of hair growth
• ensure all hairs in the area are removed
• lay 20-30 hairs, well aligned, in mineral oil on slide
• examine under coverslip
• look at hair root, hair shaft and distal tips

Question 9

describe the microscopic appearance of a telogen bulb

Answer 9

• spear shaped
• rough
• no pigment

Question 10

describe the microscopic appearance of an anagen bulb

Answer 10

• rounded
• smooth
• pigmented centre +/-
• bulb may fold around shaft when plucked

Question 11

what is a follicular cast

Answer 11

“collars” f keratin around the shaft of hair
seen in many diseases where increased keratin produced in the hair follicle

Question 12

describe the appearance of normal hair tips and what is indicated abnormal shafts

Answer 12

normal = smooth pointed tips
angular broken ends indicate self inflicted hair loss and probable pruritus

Question 13

what is a woods lamp examination and when do you use it

Answer 13

• used in any suspected case of ringworm
  1. preheat the lamp for 5 minutes before using, illuminate the area of interest in a darkened room. positive result will show green fluorescenes along the hair shaft

Question 14

what equipment is needed for skin surface cytology sampling

Answer 14

• miroscope slides
• adhesive acetate tape
• cotton buds
• needles
• syringes
• diff quick (romanowsky stain)
• immersion oil
• lens tissue
• pencil/permanent marker for labelling
• microscope with oil immersion (100x) objective

Question 15

describe the process of taking a direct impression smear, when you would choose this sampling method and what information is given

Answer 15

• press glass slide directly on surface of lesion, air dry and stain
• useful for moist exudative and ulcerated lesions in accessible areas
• gives info on surface only, not deeper tissue

Question 16

describe the process of doing an impression smear on a pustule. why is this helpful

Answer 16

1. insert fine (25-27G) needle into pustule (parallel to skin so not puncuring tissue below pustule)
2. impress a microscope slide directly onto the pustule contents. air dry and stain

helps differentiate bacteria vs sterile pustules and can be used to detect acantholytic keratinocytes

Question 17

describe the process of taking a cotton bud swab sample and where you would use this method

Answer 17

for ear canal cytology and dryer skin surface (especially in inaccessible for direct impression smear)
1. insert swab into ear canal to appropriate depth to sample exudate OR roll cotton bud on the skin surface (moisten swab with sterile saline if necessary first)
2. roll sample onto microscope slide, heat fix/air dry and stain

Question 18

describe the process of acetate tape strip and when it is useful (stained)

Answer 18

used for dry, scaly skin or to sample folds (interdigital area)
1. press sticky surface of tape onto the area to be sampled, will collect surface cells and microorganisms
2. stick tape on edge of microscope slide so can dip tape into stain, using slide as handle
3. DO NOT use fixative for tape and makes it brittle/cloudy. sample is fixed already on tape
4. dip in eosin and methylene blue then fold over so adhesive side of tape sticks to slide and blot (rinse optional)
5. label slide
6. view through tape (no need for coverslip

tape goes cloudy if kept, if plannin on sending to lab better to do impression smear

Question 19

when should you use skin surface swabs (sterile)? what scan be sampled

Answer 19

• if need to know precise identity of bacterium or antibiotic susceptibility pattern
• can sample exudate from ears, contents from fresh pustule/bulla, skin under margin or epidermal collarette or under crust, surface microorganisms if appropriate

send to lab in transport medium

Question 20

when do you use a dermatophyte culture and how is it done

Answer 20

used in any patient with suspected dermatophyte infection
- if no clearly circumscribed lesion or suspect asymptomatic carrier, use McKenzie brush technique: brush coat with sterile toothbrush
- if discrete lesion present, sample edge of lesion with sterile hemostats and a scalpel blade (without oil) to collect hairs and scale (try to collect smaples that fluoresce under woods lamp if possible)
- package whole sample in PAPER envelope to submit to external lab for culture OR
- carefully place hairs and scale into dermatophyte test medium if culturing in house using sterile needle

Question 21

if a pet is on antibiotics and a sample is needed for bacterial culture, what must be done?

Answer 21

remove patient from antibiotics 5-7 days prior to sampling

Question 22

what medium should a tissue sample be placed in if sending for bacterial culture

Answer 22

sterile saline or sterile saline soaked swab
NOT formalin as will kill organisms

Question 23

when is the 4x objective used

Answer 23

to examine coat brushings, hair plucks, skin scrapes, flea dirt or hair structure

Question 24

when is the 10x objective used

Answer 24

to identify parasites and look more closely

Question 25

when is the 100x objective sued

Answer 25

to examine cytology samples, pus, FNAs, on this power you should be able to identify cell types and organisms