Approach to pruritis

What is pruritus?

Unpleasant sensation that elicits the desire or reflex to scratch

Why is it hard to notice pruritis in cats?

May be secretive

What does pruritis look like in dogs vs cats?

• Dogs —> scratching, rubbing (along furniture), chewing, licking, rolling, temperament changes

• Cats —> scratching, chewing, licking

What is being shown here?

Marked excoriation associated with scratching + alopecia secondary to chronic skin inflam

What is being shown here?

• Alopecia due to excessive licking

• Often symmetrical

What is being shown here?

Excoriations as a result of severe scratching in very pruritic cat

What history information would you try to gather from a patient with pruritis?

• Observe dog in consult room / cat in basket

• Videos of animal at home

• Hair in environment or faeces, vomiting hairballs

What do we do in a physical examination?

• See saliva staining, excoriations, hair embedded in gingival sulci/tongue

• Feel broken hair

• Itch-scratch reflex —> under ventrum (backleg will begin to try and scratch)

How can you diagnose pruritis?

Trichography —> broken hair tips

Cytology —> oropharyngeal bacteria

What is being show here

Conchiformbius bacteria —> if found on animals feet it is a sign that they have been licking (oral comensal)

What are the animal welfare concerns of pruritis?

Chronic unpleasant sensation, lack of sleep

What are the different types of pruritis?

• Primary

  • Pruritus is the initial sign

  • Other lesions (alopecia, excoriations, pustules, crusts) follow

• Secondary

  • Lesions such as pustules, nodules, scale or crusts precede pruritus

What are the ddx for pruritis?

• Hypersensitivity (allergic skin disease)

  • Canine atopic dermatitis

  • Feline atopic skin syndrome

• Parasitic infection

• Microbial infection (secondary to other skin disease)

• Some disease have variable pruritis

What are causes of primary pruritis?

• All forms of HSR (type I and/or IV)

• canine atopic dermatitis /feline atopic skin syndrome, parasite hypersensitivity (including Demodex gatoi & injai)

What can cause secondary pruritis?

• Microbial infection —> pruritus usually present with other lesions

• Demodex canis/cati, dermatophytosis, PF and Epitheliotophic lymphoma: present with another major sign +/- pruritus

What are some examples of diseases that occur at specific ages?

• canine atopic dermatitis/feline atopic skin syndrome onset <3yrs

• Epitheliotropic lymphoma in seniors

• pemphigus foliaceus in middle aged

What diseases are contagious?

• Parasites (Sarcoptes, Cheyletiella, Demodex gatoi, fleas)

• Dermatophytosis

In what disease is pruritis often very severe?

Sarcoptic mange

Which conditions cause pustules?

• Bacterial infection —> superficial pyoderma

• Pemphigus foliaceus (Akitas predisposed to)

What is the pruritis visual analogue scale useful for?

Pruritis severity:

assesses tx response & important for dogs with multiple handlers / owners

not helpful in narrowing differentials

What is a characteristic sign of epitheliotropic lymphoma?

Depigmentation of the skin in the mucous membranes of an old animal

What is the distribution of the lesions of epitheliotropic lymphoma, pemphigus foliaceus and canine atopic dermatitis?

CAD = feet, ears, chin, eyes, perianal, ventrum

PF = ears, nose, eyes, digits and flank

EL = nose, chin, digits and flank

What is the lesion distribution of sarcoptic mange, Cheyletiellosis & pediculosis, trombiculiasis and flea bite hypersensitivity / infestation?

What area does otodectic mange effect?

• ear canals

• ‘coffee granules’ wax

• Skin around ears and tail in cats rarely

What is Favrot’s criteria for diagnosis of canine atopic dermatitis?

• Age at onset < 3 years

• Mostly indoor

• “Alesional” pruritus at onset

• Affected front feet

• Affected ear pinnae

• Non-affected ear margins

• Non-affected dorso-lumber area

for dogs

What is the first thing we do in a pruritic case?

• Cytology to rule out secondary microbial overgrowth/infection

• Direct impression smear —> exudative lesions, ruptured pustules

• Indirect impression smear —> ear canals, skin folds

• Acetate tape impression (stained) —> glabrous skin, interdigital skin

What are the different ways we can identify parasites?

• Direct observation —> harvest mites, lice, fleas (cats readily remove), Otodectes (via otoscope)

• Coat brushing and wet paper test —> fleas, cheyletiella

• Acetate tape impression (unstained) —> Demodex gatoi, Cheyletiella

• Skin scraping

• Hair plucks and trickography —> Demodex injai (less invasive)

What is being shown here?

Harvest mites

• Orange clusters on skin

• 6 legs = juvenile (larval) form of the mite

What is being shown here?

Sarcoptes scabei —> diagnostic of sarcoptic mange

L = adult mites

R = faecal pellets + eggs

How do you rule out ectoparasites?

Ectoparasite treatment trial

How do you rule out food-induced canine atopic dermatitis?

Elimination diet

When would you carry out a skin biopsy?

If history and lesions consistent with pemphigus foliaceus / epitheliotropic lymphoma

What is causing this?

Fleas

erythema, excoriation, pruritis, caudal dorsum + HLs

What is causing this?

Sarcoptes scabei → sarcoptic mange

elbows crusty, erythema, pinnal margins affected

only seen in older, dehbilitated cats

What is causing this?

Notoedres cati —> feline form of sarcoptic mange (not in UK)

affects head & ears mostly (rare in rest of body), zoonotic

Cheyletiellosis vs pediculosis

Pediculosis on the left

Sarcoptes vs notoedres

Sarcoptes = right

notoedres = smaller, bum hole dorsal

Cheyletiella vs Otodectes

Otodectes = right —> long strands on legs

cheyletiella = left —> waisted body, long legs, hooked palps

Ear mites vs harvest mites

harvest mites = left

ear mites = right

Cheyletiellosis vs pediculosis

cheyletiella = right —> causes bigger hypersens reaction = lots of scale (walking dandruff)

pediculosis = left (lice)

Cheyletiella vs louse egg

Louse egg = right = cemented to hair + operculated

cheyletiella = left = not operculated, loosely attached to hair

What are the different types of lice?

• Chewing lice —> Felicola subrostratus, Trichodectes canis (broad heads)

• Sucking louse —> Linognathus setosus (narrow heads)

What species of demodex affect which species?

• Cats

  • Demodex gatoi (very pruritic + alopecia)

  • D. cati (just hair loss due to inflam of hair follicles)

• Dogs

  • D. canis (follicular, patchy to widespread alopecia)

  • D. injai (terrier breeds pruritis i.e. wirey coated breeds —> affects dorsum of shoulders)

What do we use to treat fleas?

Adulticide (correctly administered) to ALL in contact animals for 6-8 weeks —> fipronil, isoxazolines (end in laner), imidacloprid

How would we treat the environment when there are fleas present?

• Vacuuming plus combined adulticide & insect growth regulator sprays e.g. permethrin

• Lufenuron (Program) injection for cats (does not kill adult fleas) —> IGR

  inform owners that adult fleas may still emerge from pupae

• Nitenpyram / spinosad / isoxazolines —> limitt egg production

What do we use to treat harvest mites and cheyletiella?

Fipronil spray (not licenced)

How do we treat hypersensitivity reactions?

• Prednisolone 0.5-1 mg/kg pruritus & skin inflammation

• Oclacitinib/lokivetmab if just pruritus (>12m old for oclacitinib)

What can heavy flea infestation of puppies and kittens cause?

Iron deficiency anaemia

What are some vector-borne diseases?

Bartonella henselae —> bartonellosis (cat-scratch fever) in humans

Dipylidum caninum (tapeworm of cats & dogs)

What are the features of the gross lesions of Epitheliotropic lymphoma?

• Lichenificaton

• Mucosal lesions

How do you diagnose Epitheliotropic lymphoma?

Skin biopsy & histopathology

What causes Epitheliotropic lymphoma and what causes the pruritis?

• Lymphocyte invasion of epidermis

• T-cells produce IL-31 → pruritis

What can damage to basement membrane often cause?

Depigmentation