The approach to pruritus Flashcards
What is pruritis?
Unpleasant sensation that elicits the desire or reflex to: scratch, Rub, Lick, Chew, Rolling
How do dogs show signs of pruritis?
- Scratch
- Rub
- Nibble
- Lick (often not perceived as pruritus by owners)
- Temperament changes
How do cats show signs of pruritis?
- Often secretive and not noticed by owners
- Alopecia due to overgrooming
- Hair plucking resulting in vomiting hairballs and hair in faeces
- Tufts around the house
What is primary pruritis?
- Itch is principal initial sign
- Other lesions such as alopecia, excoriations and secondary infection follow
What is secondary pruritis?
- Lesions such as pustules, nodules, scale or crusts precede the onset of pruritus
- 2˚ ~ most commonly due to superficial bacterial pyoderma or Malassezia
What are some manifestation of pruritis in dogs?
- Recurrent pyoderma
- Recurrent otitis
- Scale, dryness and grease -> smell
- Alopecia
- Behaviour changes
What are some manifestation of pruritis in cats?
Reaction patterns
- Alopecia
- Head and neck pruritis
- Eosinophilic granuloma complex
- Behaviour changes
- Self trauma
Why is interpretation of skin disease due to primary pruritus is complicated by secondary skin lesions?
- Due to trauma
- Due to secondary infection
- So many skin diseases end up looking similar
How can pruritis be identified during the clinical exam?
Direct observation:
- Whilst taking history, let the dog free in the room if appropriate
- Owners may bring itch charts and videos
Look for secondary signs:
- Broken hair
- Saliva staining
Which two laboratory tests can be useful in identifying pruritis?
- Trichography
- Cytology
Hair plucks (trichography) allow examination of the…?
- State of growth e.g. anagen and telogen
- Structure of the melanosomes
- Pathological changes
- Attached/associated organisms and parasites
Which pathological changes to the hair may be seen using trichography?
- Bulb e.g. alopecia areata
- Shaft e.g. dermatophytosis
- Tip e.g. damage through self trauma or clipping
- External surface e.g. Follicular casts
How do you differentiate primary and secondary pruritis?
- Is it a rash that itches or an itch that rashes?
- Does the itch resolve with treatments for infections?
- Is there is pruritus only where this is infection, but marked lesions elsewhere?
Give some examples of skin infections that cause pruritis
- Superficial bacterial pyoderma
- Malassezia dermatitis
- Malassezia, Staphylococcal and Pseudomonas otitis
Give some examples of ectoparasites that cause pruritis
- Sarcoptes scabei var canis / Notoedres cati
- Demodex gatoi
- Cheyletiella spp
- Fleas
- Lice
- Otodectes cyanotis
How does superficial pyoderma present?
Spots, crusts and patchy hair loss
What are the 4 main clinical signs of Malassezia dermatitis
- Erythema
- Pruritus: often severe facial irritation
- Malodour
- Dark coloured exudate
What is the genus and species of the main flea associated with infestation and disease in the UK?
Ctenocephalides felis
What is the reaction associated with fleas?
Flea allergic dermatitis
- Type I and Type IV hypersensitivity reactions
What are the primary signs of Ctenocephalides felis?
Pruritis
Papules
Erythema
What are the secondary signs of Ctenocephalides felis?
Excoriation
Alopecia
Crusts
Pyoderma
In which part of the fur does alopecia secondary to a flea infestation occur?
Caudodorsally
How is Ctenocephalides felis diagnosed - 3 methods?
- Direct observation – good in severe infestation, but unreliable
- Wet paper test – brush and comb coat onto damp paper and observe digested blood in faeces
- Coat brushings / sellotapes – direct microscopy may reveal coiled faeces or occasional find fleas
How are fleas managed and treated?
- Early environmental control: cleaning, vacuuming, environmental sprays
- Adulticide to all animals
Sarcoptic mange is caused by which parasite?
Sarcoptes scabei var canis
Which species are affected by sarcoptic mange?
Dogs and immunosuppressed cats
Describe the pathogenesis of sarcoptic mange
- Induce marked type I hypersensitivity reaction
- Pruritus starts 3-4 weeks after infestation
- Female mites make tunnels in the stratum corneum, feeding and lay eggs. Males more commonly on surface
What are the primary signs of sarcoptic mange?
Pruritis
Papules
Erythema
What are the secondary signs of sarcoptic mange?
Excoriation, alopecia, crusts, pyoderma signs
Where on the body is most affected by sarcoptic mange?
Ears, ventral chest, elbows and hocks
How is sarcoptic mange diagnosed?
- Skin scrapes: high specificity (100%) & low sensitivity (50%)
- Serology: variable sensitivity and susceptibility
How is sarcoptic mange treated?
Common topical and oral treatments are useful:
- Moxidectin
- Selamectin
- Isoxazolines
Environmental control using cleaning, vacuuming and sprays
Which 2 Demodex species are associated with primary pruritis?
Demodex injai - dog
Demodex gatoi - cat
Most species of Demodex are associated with which signs?
Alopecia
Comedone formation
Secondary infection
Which dogs species are most commonly affected by Demodex injai?
Terriers - border, welsh, west highland
- early adulthood age of onset
What are the clinical signs of Demodex injai?
- Greasiness
- Truncal pruritus and alopecia (2˚)
- Variable 2˚ bacterial infection
How is Demodex injai diagnosed?
Deep skin scrapes and biopsy
- mites live deep in follicles and sebaceous glands
What is the genus and species of harvest mites?
Neotrombicula autumnalis
What are the clinical features of a harvest mite infection?
- Localised pruritis at the site of larval attachment
- Orange dots on skin
- Seen seasonally from mid June to the end of September
How are harvest mites treated?
Fipronil spray for the legs is often recommended (not licenced)
What is the name given to ear mites?
Otodectes cyanotis
How is Otodectes cyanotis diagnosed?
- Direct observation of photophobic mites using otoscope
- Ear wax examination
- Take wax using a swab or curette and mix gently with liquid paraffin to avoid bubbles
- Mites and elongated eggs are diagnostic
What are the signs of Cheyletiella infection?
- Scale affecting the trunk and sometimes around the head
- Miliary dermatitis in the cat
- Variable pruritus
- Alopecia
- Marked self trauma
How is a Cheyletiella infection diagnosed?
- Coat brushings – crawling dandruff
- Skin scraping from scaly areas
- Faecal flotation has been used in cats where excessive grooming is present
What are the features of food hypersensitivity reactions?
- young age of onset
- pruritis
- resembles atopic dermatitis
- 2 or more cutaneous reaction patterns in cats
How are food hypersensitivity reactions diagnosed?
Strict food trial
What are the features of atopic dermatitis and where on the body is affected?
- young age of onset
- bilateral symmetrical pruritus affecting the ventral abdomen, axillae, feet, face and ears initially, often complicated by 2˚ infection
Describe pemphigus foliaceus and its characteristics
- Disease of adult dogs and cats
- Characterised by sterile pustule/crusts affecting the face, nose and feet particularly
- Can be very pruritic
Describe epitheliotropic lymphoma, its signs and presentation
- Disease of older dogs
- Lymphocyte invasion of epidermis causes depigmentation, ulceration and plaques
- Can be pruritic
- Variable presentation means that dogs may look like atopic dermatitis (but age is a big flag that cAD is not likely)
