Intro to Dermatology and Diagnostic methods

Question 1

1. Pruritus and causes.
2. With what disorders can scale be seen?
3. What is alopecia?
4. What is a bulla?

Answer 1

1. Itching - allergy, parasites, microbial infection/overgrowth, otitis.
2. Keratinisation disorders.
3. Hair loss - can be secondary.
4. Localised collection of fluid >1cm in diameter and larger than a vesicle.

Question 2

1. What is erythema?
2. What is a macule?

Answer 2

1. A diffuse or localised redness of the skin which disappears with diascopy.
2. A flat circumscribed skin discolouration <1cm in diameter without surface elevation or depression.

Question 3

1. 2 main causes of skin being red?
2. How can these be differentiated?

Answer 3

1. Erythema = blood in blood vessels. Haemorrhage = blood outside of blood vessels.
2. Diascopy - place glass slide over the area of redness.
   Erythema will blanch as vessels are compressed, haemorrhage will not blanch.

Question 4

1. What is a nodule?
2. What is a papule?

Answer 4

1. Circumscribed solid elevation greater than 1cm usually extending into the dermis, large nodules may be referred to as masses.
2. A small solid elevation of the skin up to 1cm in diameter, feels solid and is due to the infiltration of inflammatory cells, fluid or foreign material, w/ oedema and epidermal hyperplasia.

Question 5

1. What is a patch?
2. What is a plaque?
3. What is a pustule?

Answer 5

1. A localised flat change in the skin pigmentation larger than 1cm in diameter (big macule).
2. Flat topped elevation of the skin >0.5cm formed by a coalition of papules; flatter than a nodule.
3. A small circumscribed elevation of the epidermis filled w/ purulent material.

Question 6

1. What is a vesicle?
2. What is a wheal?

Answer 6

1. Small circumscribed elevation of the epidermis fille with a clear fluid <1cm in diameter.
2. A sharply circumscribed raised lesion consisting of oedema; usually appears and disappears w/in minutes to hours.

Question 7

Causes of secondary lesions.

Answer 7

Scratching, chewing, other trauma.
- as a result of infections or may evolve from regressing primary lesions.

Question 8

1. What is a comedone?
2. What is crust?
3. What is an epidermal collarette?

Answer 8

1. Dilated hair follicle filled w/ cornified cells and sebaceous material. Blackheads.
2. Dried exudate, cells, pus and scale adherent to the surface.
3. A circular lesion w/ a marginal rim of scale.

Question 9

1. Excoriation/ erosion?
2. Fissure?
3. Hyperpigmentation.
4. Hypopigmentation.

Answer 9

1. Superficial damage to the epidermis.
2. Linear cleavage into the epidermis.
3. Too much pigment.
4. Too little pigment.

Question 10

1. Hyperkeratosis?
2. Lichenification?

Answer 10

1. Increase in thickness of the cornified layer of the skin.
2. Thickening of the skin as a whole resulting in cobblestone appearance.

Question 11

1. What is scale?
2. Scar?
3. Ulcer / ulceration?

Answer 11

1. Accumulation of loose fragments of cornified layer of the skin.
2. Fibrous replacement tissue formed when there has been trauma.
3. Full thickness loss of epidermis, exposing the dermis.

Question 12

Diagnostic approach of a dermatological case.

Answer 12

General history:
- other body systems affected.
- concurrent disease.
- lifestyle and exposure:
– environment.
– contagion.
- in-contact people and animals.
– contagion and zoonosis.
- diet.
Ectoparasite control.
Identify primary problem.
First sign?
Progression?
- lesion development.
- severity.
Chronic disease.
- seasonal.
- wax and wane.
Response to Tx.
- used appropriately?

Question 13

Diagnostic techniques in dermatology.

Answer 13

Acetate tape:
- Malassezia, bacteria, inflammatory cells.
Skin scraping:
- Deep – demodex mites.
- Superficial – Cheyletiella, Sarcoptes, Chorioptes, Psoroptes (livestock).
Cytology.
Flea comb - fleas, Cheyletiella.
Trichogram (hair pluck) - demodex, anagen, telogen, mite and lice eggs, evidence of pruritus, dermatophytosis (ringworm), hair shaft abnormalities.

Question 14

Advantages of cytology.

Answer 14

Quick, easy, cheap.
Gives a lot of info about what dealing with.

Question 15

How would a skin scrape be taken from a larger animal e.g. horse w/ itchy distal limb.

Answer 15

Wooden tongue depressors to scrape material from skin surface into a petri dish.

Question 16

Indications for allergen testing.

Answer 16

Identify the allergens for potential clinical significance in canine atopic dermatitis or cats w/ feline atopic skin syndrome or horses with allergic skin disease - NOT a diagnostic test.
Provide allergen specific immunotherapy:
- Allergy vaccine / desensitisation / immunotherapy.
- Only use allergen tests w/ high compliant owners who understand limitations of the test and ASIT.
- Need to correlate with history e.g. seasonal or consistent.
Testing younger animals may give a narrower repertoire of allergens than they will have as some hypersensitivities take longer to develop.
Intradermal test.

Question 17

1. Intradermal test positive control.
2. Intradermal test negative control.

Answer 17

1. Histamine.
2. Saline.

Question 18

Allergen specific IgE serology testing in dogs.

Answer 18

Heska Allercept test is based on the capture of IgE antibody by the Fc epsilon RI receptor:
- receptor normally binds IgE to a mast cell in vivo.
- binding highly specific for IgE antibody.

ELISA that measures serum IgE using a panel of monoclonal (polyclonal) antibodies specific for dog IgE.
- antigens coated on the ELISA plate.

Tests use a variety of allergen panels including indoor and pollen allergens and fleas.
Only a guide.
“Screening” tests are poorly validated.
Only clinically significant if history relevant.

Question 19

Allergen serology tests that are available.

Answer 19

Malassezia - dubious benefit, no proof that positive dogs are hypersensitive or that they will respond well to ASIT.
Staphylococci - again dubious clinical benefit.
Other tests incl. cytology and culture should be used to explore importance of microbial antigens as a cause of pruritus.
Food serology NOT recommended for selecting diets for trialling or diagnosis if “food allergy”.

Question 20

Other dermatological diagnostic testing.

Answer 20

Culture:
- bacterial.
- fungal.
- Mycobacteria.
- Susceptibility testing - only helpful for systemic, not topical treatment.
PCR e.g. dermatophyte.
Dermatopathology - biopsy and microscopy.