Dermatological Sampling And Practical Techniques Notes

Dermatological sampling and practical techniques

1. Coat brushing/combing

Place debris from coat brushings onto moistened paper to examine

• Flea dirt.

Examine coat combings in liquid paraffin under a coverslip under the microscope.

• Cheyletiella mites or eggs

2. Acetate tape strip (unstained)

Used to sample for Cheyletiella or for lice.

The tape is pressed over multiple sites of scaling and dragged across the hairshafts. It is then placed directly on the slide without staining.

3. Skin scrapings

Skin scrapes may be deep or superficial

Superficial skin scrapes are diagnostic for surface parasites such as Cheyletiella, Neotrombicula and Otodectes, and for dermatophyte spore infection of hair shafts.

Deep skin scrapes are required for deeper parasites such as Demodex and Sarcoptes.

The hair should be clipped from around the area to be sampled. Mineral oil is placed onto a scalpel blade and a few drops placed on the skin. The skin should be squeezed prior to sampling. The blade is scraped over the skin surface at a 90 degree angle to the skin in the direction of the hair growth.

For a superficial scrape, there is no need to draw blood. For a deep skin scrape, keep going until blood is seen.

The material is deposited on one or more slides in mineral oil and covered with a coverslip.

4. Trichograms

Trichogram involves plucking hair. The hairs are suspended in liquid paraffin and examined under a coverslip.

The hairs should be plucked near their base with fine forceps in the direction of hair growth.

Telogen bulbs are spear shaped and rough. These are inactive hairs and are normally present in around 80-90%. In endocrinopathies, 100% of hairs will be in telogen.

Anagen bulbs are rounded and smooth. They are actively growing hairs and usually account for 10-20%.

There are many breed and seasonal variations of distribution of anagen and telogen.

Trichograms are also useful for assessing dermatophytosis. These hairs should be stained with lactophenol cotton blue to show hyphae and arthrospores on the hair.

Clumps of melanin are seen in the hairs of dogs with colour dilution alopecia.

Follicular casts are collars of keratin seen around the hair shaft. These are seen in diseases where increased keratin is produced in the fair follicle. This include sebaceous adenitis, demodicosis, dermatophytosis, endocrinopathies and vitamin A associated dermatosis.

Angular and broken hair tips indicate self-inflicted hair loss.

5. Skin biopsies

Skin biopsies are useful for scarred and chronic lesions.

Sedation and local anaesthesia or general anaesthesia may be required depending on the animal.

The aim should be to take a fully developed primary lesion where possible, avoiding traumatised skin.

• For alopecia – biopsy the area of maximum hair loss, the margin of the alopecic area and normal haired skin

• For ulcerated skin – biopsy the ulcerated area, area just adjacent to the ulcer and where the epidermis is still intact.

• For pustules, vesicles or bullae – remove the whole lesion without disruption.

The site should be clipped using scissors. A circle should be draw around the lesion in indelible marker, as well as an orientation line along the line of hairgrowth.

Punch biopsies are commonly used. They should be help perpendicular to the skin surface and rotated in one direction.

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