Logical approach to skin diseases

Question 1

What does caudo-dorsal pruritis suggest?

Answer 1

Fleas (flea allergic dermatitis)

Question 2

Distribution of pruritis in feline atopic syndrome (food allergy)

Answer 2

Intense on head, also on neck and caudal ventrum

Question 3

Distribution of pruritis in flea bit hypersensitivity in cats

Answer 3

Head
Caudal ventrum
Caudal dorsum
Tail

Question 4

Primary skin lesions

Answer 4

Initial eruption / change that develops as direct reflection of underlying disease

Question 5

Examples of primary skin lesions

Answer 5

Papule, plaque, pustule, wheal, nodule, tumour, cyst, vesicle, bulla.

Question 6

Follicular vs non-follicular primary skin lesions

Answer 6

Non-follicular example is superficial pyoderma, ‘puppy’ pyoderma.

Follicular needs more aggressive treatment.

Question 7

Secondary skin lesions

Answer 7

Evolve from primary lesion or are artefacts induced by the patient.

Epidermal collarette, scar, excoriation, ulcer, fissure, callus, lichenification.

Question 8

Seborrhoea sicca

Answer 8

Moth eaten, patches of alopecia with hyperpigmentation – follicitis characteristic.

Erythema.

Demodex, bacterial folliculitis, dermatophytosis.

Question 9

Wet paper test

Answer 9

For parasites

Brush debris from coat on to wet paper.

Dark charcoal flea dirt -> red provides evidence of flea infestation.

Question 10

Coat brushings

Answer 10

Coat brushings dry onto slide (walking dandruff).

Good for finding Cheyletiella.
□ Dogs – C. yasguri.
□ Cats – C. blakei.
□ Rabbit – C. parasitivorax.

Question 11

Accetate tape impressions

Answer 11

Useful for harvest mite – pruritis.

Acetate strip into lateral pouch of cat.

Question 12

Sellotape and Scotch tape preparations

Answer 12

Used to pick up surface mites e.g. Cheyletiella.

Attach to glass slide and examine.

Particularly useful for “small furries” and Neotrombicula autumnalis.

Scotch-tape Diff-Quick stained surface preps are really helpful for cytology and Malassezia/bacteria.

Question 13

Skin scrapes

Answer 13

Can do superficial or deep.

Superficial just epidermis.
□ Choose area carefully, free from self-inflicted trauma and medication.
□ Clip hair and apply liquid paraffin.
□ Scrape gently.

Multiple surface scrapes often required for Sarcoptes.
□ Eggs and darker faeces present.

Deep.
□ Clip, squeeze, scrape, squeeze.
□ Must go deep enough to cause capillary haemorrhage if you are looking for Demodex.

Question 14

Diascopy

Answer 14

useful for differentiating between inflammatory erythema or bleeding

Question 15

Trichogram / hair plucking

Answer 15

Useful for demodex

Question 16

Direct skin smear

Answer 16

Squeeze skin and wipe gently across a clean glass slide.

Good for Demodex

Question 17

Subcutaneous Dirofilariosis

Answer 17

Dirofilarial repens – transmitted by mosquito (many different species).

Nematode – lifecycle under the skin.

Subcut nodules, facial nodular dermatitis, pruritic popular dermatitis.

Intensely pruritic facial nodules.

Question 18

Diagnosis of dermatophytes

Answer 18

Plucked hairs from periphery of lesion.
□ Examine in potassium hydroxide or stained with ink or lactophenol cotton blue.

Woods lamp examination.
□ Useful for diagnosis, obtaining material for culture and to assess treatment.
□ Ultra-violet light filtered through cobalt glass must be warmed-up.
□ Use in darkened room.
□ Hairs invaded by Microsporum canis may fluoresce apple-green.

Culture on Sabouraud’s dextrose agar or Dermatophyte Test Medium (DTM).
□ Growth is slow, but is essential for the proper identification of fungi.

Question 19

Malassezia diagnosis

Answer 19

Scotch tape preparation from the skin stuck to a glass slide, fixed and stained for cytology.

Culture on Sabouraud’s dextrose agar.

Question 20

Diagnosis of bacterial skin infections

Answer 20

Cytology including Gram stained smear.

Culture.
§ Usually Staphylococcus pseudintermedius.

Antibacterial sensitivity test.

Therapeutic trial but must ensure suitable antibiotic is given at the full dose rate for a sufficient length of time.

Question 21

Exclusion diet for allergy testing

Answer 21

Diet of a pure source of protein and carbohydrate and no tit-bits.

Give for a minimum of four weeks.

Use foodstuffs not given previously, e.g. venison and sweet potato.

Changing from one brand to another is not satisfactory.

Commercial hypoallergenic diets may be used for the management of food allergy eg HillsD/D, RCW anallegenic, Purina HA, Eukanuba Dermatosis FP.

Question 22

Intradermal skin testing for food allergy

Answer 22

Intradermal test is thought to be superior to the prick test, but false-positive and false-negative results may occur.

Requires experience to obtain reproducible results.

Patient must be off steroid or cyclosporine medication for a minimum of 4 weeks but Apoquel and Cytopoint do NOT affect skin testing so may be used.

Question 23

Methods of allergy testing (skin disease)

Answer 23

Exclusion diet

Intradermal skin testing

Serological allergy testing

Removal from home environment

Patch testing

Question 24

Patch allergy testing

Answer 24

Suspect allergen applied to skin for 48 hours.

Test sites observed for following 3 - 5 days. C

Check on normal animals that substances are not irritant.