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VET 411: Skin > Pruritus > Flashcards

Pruritus Flashcards

1
Q

pruritus

A

sensation that elicits a desire to scratch

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2
Q

clinical signs of pruritus

A
  • excessive scratching, rubbing, self-chewing, or overgrooming
  • alopecia
  • erythema
  • excoriations
  • lichenification
  • hyperpigmentation
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3
Q

sequelae to pruritus

A

secondary infections

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4
Q

atopic dermatitis

A

inflammation of the skin leading to pruritus, erythema, lichenification, discoloration, hyperpigmentation

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5
Q

what is the most common sign of food allergies

A

face and head pruritus

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6
Q

pruritus vs inflammation

A

NOT the same thing

pruritus can be a sequelae or an inducer of inflammation

often seen concurrently

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7
Q

what is the main cell involved in the pruritic pathway

A

mast cells

  • contain more receptors and mediators than any other cell
  • required for wound healing and establishing skin barrier
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8
Q

what is unique about mast cell’s after degranulation

A

able to resynthesize mediators after degranulation to continue to function

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9
Q

histergenic itch

A
  1. antigenic stimulation
  2. antigen binds IgE on mast cell
  3. induces histamine release
  4. histamine interacts with sensory neurons
  5. induces itch sensation
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10
Q

non-histergenic itch

A
  1. antigenic stimulation
  2. antigen binds Mrgprb2 on mast cell
  3. induces tryptase release
  4. tryptase interacts with sensory neuron
  5. induces itch sensation
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11
Q

what is the most abundant mediator stored in mast cell granules

A

tryptase

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12
Q

dermatomes

A

areas of skin that send information to the brain via a spinal nerve

contain large number of sensory nerves that end in FREE NERVE ENDINGS

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13
Q

free nerve endings

A

transmit touch, temperature, pain, and pruritus

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14
Q

how do dermatomes transmit pruritus

A
  1. keratinocytes release inflammatory mediators
  2. binds to receptors on the sensory neurons
  3. carries the itch sensation from free nerve endings to the brain via non-myelinated, slow conducting C fibers
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15
Q

what senses do C fibers transmit

A

pain, pruritus, heat

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16
Q

what spinal tract carries pain and itch (histamine and non-histamine) sensations to the brain

A

contralateral spinothalamic tract

17
Q

effect of pain on pruritus

A

pain inhibits pruritus

animals will scratch to the point of hurting themselves to get the itch to stop

18
Q

scrapie

A

prion disease in sheep and goats

causes damage to the inhibitory gating mechanism for itch in the midbrain

19
Q

what are the three theories of how pain and pruritus are transmitted differently

A
  1. specificity
  2. pattern
  3. central processing
20
Q

specificity

A

different subsets of nociceptors transmit pain vs pruritus

(they each have their own peripheral and central neurons)

21
Q

pattern

A

spatio-temporal pattern (location of the neural activity on the skin) permits distinction

22
Q

central processing

A

the brain differentiates between pain and pruritus

23
Q

why is it difficult to differentiate between pain and pruritus in animals

A

animals will often lick at painful sites as well as itchy sites

24
Q

what are the mediators of pruritus

A
  1. histamine
  2. proteases
  3. interleukins
  4. substance P
  5. leukotrienes
  6. opioid peptides
25
Q

histamine receptors

A

H1 and H4: activating; elicit itch

H3: inhibiting; blocks itch

26
Q

effect of benadryl

A

H1 receptor blocker

not proven effective for canine pruritus

27
Q

proteases & protease receptors

A

endogenous: tryptase
exogenous: mites, bacteria, fungi
- mama animals are allergic to proteolytic enzymes in insect saliva

receptors: PAR-2

28
Q

interleukin pruritus mediators

A

IL-31: bind keratinocytes
IL-4 and 13: atopic dermatitis; stimulate IgE and IgE from B cells
IL-5: insect allergies; stimulate eosinophils

29
Q

cytopoint vs apoquel

A

cytopoint: inhibits IL-31
apoquel: inhibits JAK-1 signaling (further down IL-31 pathway)

30
Q

substance P

A

involved in CNS and sensory neurons

31
Q

what medications affect substance P function

A
  • capsaicin
  • maropitant (cats)
32
Q

leukotrienes

A

LTB4; associated with essential fatty acid metabolism

33
Q

opioid peptides

A

Mu receptors

**do NOT give a pruritic animal opioids

34
Q

what environmental factors worsen pruritus

A

heat and dryness

35
Q

effect of gabapentin & pregabalin on pruritus

A

GABA analogs - used as a last resort for neurologic pruritus

36
Q

effect of corticosteroids on pruritus

A

decrease neutrophil migration, circulation of eosinophils, basophils, monocytes, macrophages, and production of pro-inflammatory cytokines

affect many steps of the pruritic pathway

37
Q

effect of cyclosporine on pruritus

A

inhibits T cell activation

38
Q

threshold phenomenon

A

what happens IN the animal

a certain pruritic load may be tolerated without provoking clinical signs, but increasing that load may push the individual over their threshold and initiate clinical signs

39
Q

summation of effect

A

what happens TO the animal

additive pruritic stimuli from different chemical mediators or coexistent skin diseases may raise an animal above its individual pruritic threshold

VET 411: Skin (16 decks)

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