Pruritus

Question 1

pruritus

Answer 1

sensation that elicits a desire to scratch

Question 2

clinical signs of pruritus

Answer 2

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

Question 3

sequelae to pruritus

Answer 3

secondary infections

Question 4

atopic dermatitis

Answer 4

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

Question 5

what is the most common sign of food allergies

Answer 5

face and head pruritus

Question 6

pruritus vs inflammation

Answer 6

NOT the same thing

pruritus can be a sequelae or an inducer of inflammation

often seen concurrently

Question 7

what is the main cell involved in the pruritic pathway

Answer 7

mast cells

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

Question 8

what is unique about mast cell’s after degranulation

Answer 8

able to resynthesize mediators after degranulation to continue to function

Question 9

histergenic itch

Answer 9

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

Question 10

non-histergenic itch

Answer 10

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

Question 11

what is the most abundant mediator stored in mast cell granules

Answer 11

tryptase

Question 12

dermatomes

Answer 12

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

Question 13

free nerve endings

Answer 13

transmit touch, temperature, pain, and pruritus

Question 14

how do dermatomes transmit pruritus

Answer 14

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

Question 15

what senses do C fibers transmit

Answer 15

pain, pruritus, heat

Question 16

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

Answer 16

contralateral spinothalamic tract

Question 17

effect of pain on pruritus

Answer 17

pain inhibits pruritus

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

Question 18

scrapie

Answer 18

prion disease in sheep and goats

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

Question 19

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

Answer 19

1. specificity
2. pattern
3. central processing

Question 20

specificity

Answer 20

different subsets of nociceptors transmit pain vs pruritus

(they each have their own peripheral and central neurons)

Question 21

pattern

Answer 21

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

Question 22

central processing

Answer 22

the brain differentiates between pain and pruritus

Question 23

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

Answer 23

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

Question 24

what are the mediators of pruritus

Answer 24

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

Question 25

histamine receptors

Answer 25

H1 and H4: activating; elicit itch H3: inhibiting; blocks itch

Question 26

effect of benadryl

Answer 26

H1 receptor blocker not proven effective for canine pruritus

Question 27

proteases & protease receptors

Answer 27

endogenous: tryptase exogenous: mites, bacteria, fungi - mama animals are allergic to proteolytic enzymes in insect saliva receptors: PAR-2

Question 28

interleukin pruritus mediators

Answer 28

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

Question 29

cytopoint vs apoquel

Answer 29

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

Question 30

substance P

Answer 30

involved in CNS and sensory neurons

Question 31

what medications affect substance P function

Answer 31

- capsaicin - maropitant (cats)

Question 32

leukotrienes

Answer 32

LTB4; associated with essential fatty acid metabolism

Question 33

opioid peptides

Answer 33

Mu receptors **do NOT give a pruritic animal opioids

Question 34

what environmental factors worsen pruritus

Answer 34

heat and dryness

Question 35

effect of gabapentin & pregabalin on pruritus

Answer 35

GABA analogs - used as a last resort for neurologic pruritus

Question 36

effect of corticosteroids on pruritus

Answer 36

decrease neutrophil migration, circulation of eosinophils, basophils, monocytes, macrophages, and production of pro-inflammatory cytokines affect many steps of the pruritic pathway

Question 37

effect of cyclosporine on pruritus

Answer 37

inhibits T cell activation

Question 38

threshold phenomenon

Answer 38

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

Question 39

summation of effect

Answer 39

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