Logical approach to skin diseases Flashcards
What does caudo-dorsal pruritis suggest?
Fleas (flea allergic dermatitis)
Distribution of pruritis in feline atopic syndrome (food allergy)
Intense on head, also on neck and caudal ventrum
Distribution of pruritis in flea bit hypersensitivity in cats
Head
Caudal ventrum
Caudal dorsum
Tail
Primary skin lesions
Initial eruption / change that develops as direct reflection of underlying disease
Examples of primary skin lesions
Papule, plaque, pustule, wheal, nodule, tumour, cyst, vesicle, bulla.
Follicular vs non-follicular primary skin lesions
Non-follicular example is superficial pyoderma, ‘puppy’ pyoderma.
Follicular needs more aggressive treatment.
Secondary skin lesions
Evolve from primary lesion or are artefacts induced by the patient.
Epidermal collarette, scar, excoriation, ulcer, fissure, callus, lichenification.
Seborrhoea sicca
Moth eaten, patches of alopecia with hyperpigmentation – follicitis characteristic.
Erythema.
Demodex, bacterial folliculitis, dermatophytosis.
Wet paper test
For parasites
Brush debris from coat on to wet paper.
Dark charcoal flea dirt -> red provides evidence of flea infestation.
Coat brushings
Coat brushings dry onto slide (walking dandruff).
Good for finding Cheyletiella.
□ Dogs – C. yasguri.
□ Cats – C. blakei.
□ Rabbit – C. parasitivorax.
Accetate tape impressions
Useful for harvest mite – pruritis.
Acetate strip into lateral pouch of cat.
Sellotape and Scotch tape preparations
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.
Skin scrapes
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.
Diascopy
useful for differentiating between inflammatory erythema or bleeding
Trichogram / hair plucking
Useful for demodex
Direct skin smear
Squeeze skin and wipe gently across a clean glass slide.
Good for Demodex
Subcutaneous Dirofilariosis
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.
Diagnosis of dermatophytes
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.
Malassezia diagnosis
Scotch tape preparation from the skin stuck to a glass slide, fixed and stained for cytology.
Culture on Sabouraud’s dextrose agar.
Diagnosis of bacterial skin infections
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.
Exclusion diet for allergy testing
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.
Intradermal skin testing for food allergy
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.
Methods of allergy testing (skin disease)
Exclusion diet
Intradermal skin testing
Serological allergy testing
Removal from home environment
Patch testing
Patch allergy testing
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.
