Clinical signs of and approach to pruritus Flashcards
What is pruritus?
‘Unpleasant sensation that elicits the desire or reflex to scratch (rub, lick, chew)’
Classify as
Pruriceptive pruritus – due to stimulation of peripheral receptors in skin (in presence of healthy nervous system). Usually due to skin disease
Neuropathic pruritus – generated in CNS in response to
- circulating pruritogens (eg cholestasis)
- pharmacological mediators (eg intraspinal morphine)
- anatomical lesion of PNS or CNS, eg syringomyelia in CKCS
How important is pruritus?
Pruritus is a physiological self-protective mechanism, designed to remove the agent causing the sensation from the skin (eg parasite, biting insect)
But enormous consequences if inciting agent is not promptly removed…
How do dogs show they have pruritis?
- Scratch
- Rub
- Nibble (may see hair at base of incisors/canines)
- Lick – often not perceived as pruritus by owners
- Temperament changes
How do cats show pruritis?
- Often secretive and not noticed by owners
- May see
- Overgrooming
- Hair plucking
- Vomit hairballs
- Tufts of hair round house
- Hair in faeces
How do horses show pruritis?
- Rub
- Stamp
- Biting
- Scratch
- Buck/kick
- Temperament changes
What are the causes of pruritis?
Why is the signficance of microbial disease so important in treating pruritis?
- Malassezia dermatitis and bacterial pyoderma cause pruritus VERY commonly but are almost always secondary to an underlying cause.
- Need to identify and treat the infection, but also establish the underlying cause.
- To investigate underlying cause, it is important to clear these secondary infections WITHOUT USE OF CORTICOSTEROIDS and assess residual pruritus.
- If pruritus resolves fully: consider underlying immunosuppressive disease, including endocrinopathies
- If pruritus remains: consider esp allergies (and parasites if not controlled)
Draw a schematic that shows approach to dermatitis cases?
Discuss how age can inform signlament?
- Consider not only age now, but age of ONSET of first signs of pruritus (often v minor)
- important – many cases will have started several years ago!
- Most parasites can be present at any age (except Demodex usually old/young animals)
- Atopy usually 6mo-3yo onset
- CAFR onset any age
- Older animals with no prior skin disease consider
- neoplasia
- microbial infection, secondary to immunosuppression/ endocrinopathy
Outline some breed dispositions to pruritic conditions?
Staffordshire bull terrier – demodicosis, atopic dermatitis
Labrador retriever – atopic dermatitis
Bassett hound – Malassezia dermatitis
What is the ‘typical’ presentation of Atopic dermatitis (environmental atopy)?
- Age onset <3yo (usually >6mo)
- Dog lives mostly indoors
- Involvement of feet +/or pinnae
- Frequent involvement of ventrum, face, otitis externa
- Ear-margins/dorsal lumbosacral area unaffected
- History of recurrent bacterial and/or Malassezia infections
- Glucocorticoid-responsive pruritus
- No contagion
What is the ‘typical’ presentation of Cutaneous adverse food reaction (food-induced atopy)?
- Any age of onset
- Involvement of feet +/or pinnae
- Frequent involvement of face, ventrum, otitis externa
- Ear-margins/dorsal lumbosacral area unaffected
- History of recurrent bacterial and/or Malassezia infections
- +/- Glucocorticoid-responsive pruritus
- No contagion
- +/- tendency to GI disturbance, more frequent defaecation
- (NB often clinically indistinguishable from environmental atopy)
What is the ‘typical’ presentation of Sarcoptic mange?
- Any age of onset
- Increased risk if fox contact
- Pruritus, papules, crusts affecting especially (but not exclusively) pinnal margins, hocks, lateral elbows, ventrum
- Potential contagion/zoonosis
What is the ‘typical’ presentation of Canine FAD?
- Esp caudal/dorsal pruritus
- Potential contagion/zoonosis
- NB not all infested animals itch!
- (NB head/face/ventrum also frequently affected in cats)
What is the ‘typical’ presentation of Neotrombicula autumnalis (Harvest mites)?
- Seasonal history (June-Sept)
- Often feet (NB interdigital skin!), head
What are the most likely d/dx for this case:
- Case 1 Ellie
- 2yo NF EB Terrier
- Chewn feet from 9 months old
- Intermittent bilateral otitis externa
- Recent erythema and pruritus of inguinum
D/dx list
- Environmental Atopy
- Food induced atopy
- Mallasezia, dermatitis and pyoderma
- Demodicosis
Result:
This is a dog with environmental atopy with secondary mallassesia and bacterial pyoderma.
What are the most likley d/dx for this case:
Case 3 Bobby
9mo JRT ME
Generalised erythema and pruritus, esp affecting feet, ventrum, axillae, face since owned (8wk old)
No improvement with short course of corticosteroids
Mild temporary improvement with antibiotics
Other dog/owner unaffected
DDx
Demodex
