Dermatology Lecture 4

Question 1

Define the term pruritis:

Answer 1

Unpleasant sensation that provokes the desire for an animal to scratch

Question 2

Describe the path of sesnory nerve fibres of pruritis:

Answer 2

1. Primary nerve fibre endings are in dermoepidermal junction - activated by a number of pruritogenic mediators - e.g. histamine (some of these are capable of inducing sensation of pain)
2. Sensation of pain transmitted through slow conducting unmyelinated C fibres + thinly myelinated type A delta nociceptive neurons
3. Enter via afferent dorsal root ganglion neurons
4. Ascend to the brain via spinothalamic tract to the thalamus

Question 3

Explain the concept of the threshold phenomenon:

Answer 3

Certain prurutic load may be tolerated without clinical signs - small increase in stimuli may push animal over leading to clinical signs

Question 4

Breifly describe the effect of summation on pruritis:

Answer 4

Pruritic stimuli from different skin diseases can add together - producing moderate to severe pruritis - individual factor produces mild or no effect

Question 5

What are the main clinical signs of pruritis in a dog:

Answer 5

• Chewing, scratching, biting, licking, head shaking
• Roll onto back/roll against furniture

Question 6

Provide some examples of primary and secondary lesions that are associated with pruritis:

Answer 6

Question 7

Name the condition that is shown below:

Answer 7

Otitis externa

Question 8

What are the clinical signs that typically mannifest as a result of pruritis in cats?

Answer 8

Cats tend to overgroom as a result of pruritis - includes licking and rubbing - self-induced alopecia, head and neck pruritis, miliary pruritis, eosinophilic granuloma complex

Question 9

Name the reaction pattern that is shown below:

Answer 9

Miliary dermatitis

Question 10

Name the reaction pattern that is shown below:

Answer 10

Non-inflammatory alopecia

Question 11

Name the reaction pattern that is shown below:

Answer 11

Eosinophillic dermatosis

Question 12

Name the pattern that is shown below:

Answer 12

Neck and face erosion pattern

Question 13

How is pruritis often observed in horses?

Answer 13

Mannifested by rubbing, stomping, head shaking or tossing

Question 14

What are the five differentials for pruritis in a dog - ranked from most likely to least likely?

Answer 14

1. Ectoparasites (primary)
2. Infections (secondary)
3. Allergies (primary)
4. Neoplasia (primary)
5. Immune mediated (primary)