Approach to pruritus Flashcards
Pruritus overview
= unpleasant sensation that elicits the desire or reflex to scratch (rub, lick, chew)
- most common dermatological presentation in dogs, 2nd most common in cats
- important welfare and economic concern
Pruritus clinical presentation
- scratching, chewing
- licking feet (dogs)
- Scratching, chewing
- licking feet (dogs)
- Feather-plucking (birds)
- Overgrooming (=‘self-induced alopecia’) (cats)
- Also tufts of hair in house, vomiting furballs, hair in faeces
- One of the four feline reaction patterns
What are the 3 main groups of causes for pruritus?
- Hypersensitivies
- Parasites
- Microbial infections
(- others: e.g. contact irritant, autoimmune (PF), neoplasia [e.g. epitheliotropic lymphoma, MCT])
Causes of pruritus - hypersensitivities
- Environmental AD / FASS*
- Food-induced AD / FFA*
- Parasite-induced hypersensitivities (esp fleas in dogs & cats)*
- microbial hypersensitivity
- contact allergy
- drug reaction
Causes of pruritic - parasites
- Endoparasites (e.g. hookworm in dogs)*
- insects*
- fleas*
- flies
- lice
- arachnids*
- mites (burrowing, surface, demodex [variably pruritic])
Causes of pruritus - microbial infections
- bacterial pyoderma
- malassezia dermatitis
- Dermatophytosis (variably pruritic)
Approach to pruritic pt
- formulate initial ranked ddx list (from signalment, history, CE (general and dermatological)
- eliminate ectoparasites and microbial dysbiosis/infections
- distinguish between environment and food-induced AD
What species is Sarcoptic mange in?
- dogs
What species is pyoderma/malassezia dermatitis more common in?
- dogs
Age of onset for demodicosis
- young (<1y) and old -> immunocompromise
Age of onset for other ectoparasites
- any age
Age of onset for environmental AD
- 6m-3y
Age of onset for food induced AD
- any age but 30-50% <1y
Age of onset for endocriopathies (& why they cause pruritus)
- middle-aged-older
- secondary infection due to immunocompromise -> pruritus
Age of onset for neoplasia
- older
Breed predisposition for demodicosis
- Staffies
- Shar pei
Breed predisposition for canine AD
- Terriers
- Labs
- Frenchies
History questions
- Current ectoparasite regime (remember to ask about all aspects: drug, frequency, which animalstreated, environmental treatment)
- Disease progression
– Which area first affected?
– Which came first – pruritus or lesions?
-> Allergic disease – pruritus commonly precedes obvious lesions
-> Immunosuppression/endocrinopathies – no pruritus until secondary pyoderma lesions develop - How has the disease progressed?
- Evidence of contagion/zoonosis?
– Contagion: consider esp dermatophytosis, fleas, sarcoptic mange, cheyletiellosis, lice
NB care re diseases with hereditary component in related dogs, e.g. CAD, demodicosis!
– Zoonosis – as above but not lice - Evidence systemic disease?
- Seasonal?
General exam
- Evidence of systemic disease?
– Dog with dull coat, lethargy and bradycardia? -> hypothyroidism
Dog with diffuse thinning of coat, PUPD, polyphagia? -> hyperadrenocorticism
With what diseases do you see pustules?
- Usually: superficial pyoderma (staphylococcal folliculitis)
- Uncommonly: demodicosis, dermatophytosis, pemphigus foliaceus (PF)
- Rarely: other sterile pustular diseases
With what diseases do you see epidermal collarettes and crusts?
- Usually: superficial pyoderma
- Occasionally: PF
What is your top ddx for lesions affecting the caudal and dorsal regions in the dog?
- FAD
How to rule out parasites
- coat brushing/combing
- trichogram
- skin scrape
- acetate tape strips
NB investigations for fleas, Sarcoptes, Cheyletiella has low sensitivity – don’t believe a negative test -> thorough treatment trial if not on good (ideally isoxazoline) regime already
How to rule out microbial dysbiosis/infection
- cytology
- Wood’s lamp
- dermatophyte direct microscopy/culture
After eliminating ectoparasites & infection, if pruritic resolves fully what does it imply? Give examples
- implies non-pruritic underlying cause
- e.g. immunosuppressive disease (including endocrinopathy), therefore investigate as appropriate
- e.g. ectoparasites, if not previously on good ectoparasite control, therefore continue ectoparasite control
If unsure which has occurred and client/you don’t wish to investigate underlying health without further justification, continue ectoparasite control and investigate underlying health if problem recurs
After eliminating ectoparasites & infection, if pruritic remains what does it imply? Give examples
- implies other pruritic underlying disease
- usually atopic dermatitis (environmental or food-induced)
How to distinguish between environmental and food-induced AD
- Exclusion diet trial i.e. rule out food as the cause
- Exclusion diet needs to be fed for 8 weeks minimum but:
–use of prednisolone or oclacitinib can shorten time to diagnosis
–Treat for initial 2-3 week, then stop to observe response:
if pruritus recurs -> resume prednisolone/oclacitinib -> repeat cycles of treatment/observation to end of trial
if no pruritus for 2 weeks -> rechallenge with old diet
Environmental atopic dermatitis diagnosed by exclusion, what next?
- always: symptomatic control
- sometimes: identify allergens: intradermal tests/IgE serology
What is more common: food induced AD or environmental AD?
- Environmental AD
