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Jorge ENI > Pruritus > Flashcards

Pruritus Flashcards

1
Q

Define pruritus

A

Unpleasant sensation that elicits the desire or reflex to scratch

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2
Q

What does pruritus look like in a dog?

A

Scratch
Rub
Nibble
Lick
Temperament changes

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3
Q

What does pruritus look like in a cat?

A

Often secretive
Overgrooming
Hair plucking (vomit hairballs, tufts of hair around house, hair in faeces)

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4
Q

What does pruritus look like in a horse?

A

rubbing
Stamping (itchy feet)
biting
scratching
bucking/kicking
temperament changes

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5
Q

What does pruritus look like in livestock

A

Rubbing

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6
Q

What does pruritus look like in birds

A

Feather plucking

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7
Q

What does pruritus look like in small furries?

A

Scratching/barbering

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8
Q

What are the welfare issues linked with pruritus

A

Distress
Discomfort
Effect on appetite
Quality of life

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9
Q

What are the economic considerations linked with pruritus

A

loss of body condition
damage to hide/fleece

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10
Q

What is pruriceptive pruritus

A

pruritus due to stimulation of peripheral receptors in skin (health nervous system) - usually due to skin disease

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11
Q

What is neuropathic pruritus

A

Pruritus generated in the CNS in response to:
- anatomical lesions of PNS or CNS
- circulating pruritogens (stimulate nerves)
- pharmacological mediators

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12
Q

What type of fibres mediates pruritus

A

unmyelinated slow-conducting C-fibres and A-delta fibres

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13
Q

What acts as the main itch receptor in skin (pruriceptors)

A

Epidermis with free C-neuron receptors

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14
Q

What are the main chemical mediators of cutaneous itch

A

various proteases/leukotrienes/neutropins
Peptides
Prostaglandins
Cytokines e.g., IL31
histamine

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15
Q

Where do chemical mediators for cutaneous pruritus originate?

A

keratinocytes
Mast cells
Skin leucocytes: T cell (IL31), eosinophils

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16
Q

How do chemical mediators of cutaneous pruritus act?

A

Direct stimulation of intraepidermal nerve fibres (IL31)
Stimulate mast cells
Stimulate other mediators/transduction cascades

17
Q

Why is IL-31 an important chemical mediator for cutaneous pruritus

A

It is the basis of main therapeutic intervention of pruritis
Drugs to block JAK1 pathway (oclacitinib)
Monoclonal antibody therapy against IL-31 (lokivetmab)

18
Q

Why do antihistamines not work very well in dogs to treat pruritus?

A

Histamine is only one of the mediators of acute inflammatory itch in allergic dogs and it is only present for a short time at the start of allergic pruritus

19
Q

How does IL-31 cause pruritus

A

produced by activated T cells in allergic skin disease
Binds to receptors on surface of neurons in skin -> activation of Janus kinase (JAK) enzymes -> stimulate pruritic nerve impulse to brain

20
Q

What is the neural pathway that causes pruritus?

A

Sensory afferent from C-neurones in skin
Dorsal nerve root to spinal cord
Dorsal horn - synapse with spinal interneurones
Cross and ascend in lateral spinothalamic tract
Thalamus -> internal capsule
Sensory cortex

21
Q

What factors can suppress/exacerbate pruritus

A

Physical factors
Mechanical factors (rubbing, scratching causes brief suppression)
Distraction

22
Q

How can the behaviour of a dog with pruritus display the severity of the case?

A

A dog that stops eating to scratch or scratches in the practice is a serious case

23
Q

How does scratching suppress pruritus?

A

Scratch -> fast conducting A-beta neurons -> activation of inhibitory neuronal circuits -> widespread surround inhibition

24
Q

How does distraction inhibit pruritus?

A

Distraction -> increased activity in descending pathways from reticular formation -> activation of inhibitory circuits in dorsal horns of spinal cord -> closes gated mechanism -> diminishes afferent itch messages

25
Q

Explain how peripheral sensitisation changes in chronic pruritus

A

Scratching -> increased local inflammation -> production of pruritogens by inflammatory cells -> increased C-fibre responsiveness

26
Q

Explain how central sensitisation changes in chronic pruritus

A

chronic inflammation of skin -> altered perception of gentle mechanical/other stimuli -> perceives as pruritus (allokinesis) -> pruritus incited by only minor stimuli

27
Q

How does heat enhance pruritus?

A

lowers threshold of receptors to pruritus

28
Q

Explain the relevance of the pruritic threshold

A

Multiple sources of pruritus summate to exceed the pruritic threshold which lead to clinical pruritus

29
Q

What are some therapeutic interventions for pruritus?

A

Reduction of skin inflammation - corticosteroids
Blocking peripheral inflammatory mediators - lokivetmab block IL-31, antihistamines
Moisturisers
Topical cooling preparations

30
Q
A

Jorge ENI (81 decks)

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