Pruritus & Dermatological Response to Skin Damage

Question 1

• What are the two main types of pruritus?

Answer 1

Pruriceptive pruritus – stimulation of peripheral receptors in skin
Neuropathic pruritus – generated in CNS (pruritogens, pharmacological mediators, lesions)

Question 2

• What does somatosensory activity of the skin involve?

Answer 2

Mechanoreceptors, thermoreceptors & nociceptors

Question 3

• What neuropeptide mediators and receptors involved in pruritus are expressed by keratinocytes?

Answer 3

Opioids, nerve growth factor, substance P, vanilloid receptors, proteinase activated receptor (PAR2), voltage-gated ATP channels

Question 4

• What are the main nociceptors found in the epidermis?

Answer 4

Mainly unmyelinated slow-conducting C-fibres, some Aδ myelinated fibres as well

Question 5

• What factors modify the sensory cortex?

Answer 5

Emotional factors and competing cutaneous sensations

Question 6

• How might scratching inhibit itching?

Answer 6

Scratching stimulates fast conducting Aβ neurons, which activate inhibitory neuronal circuits, causing widespread surround inhibition

Question 7

• What are the actions of pro-inflammatory mediators?

Answer 7

Direct pruritogenic effect, potentiate other pro-inflammatory mediators & stimulate mast cells -> release of pruritogens

Question 8

• What are some of the common mediators of pruritus?

Answer 8

Histamine, substance P, serotonin, tryptase, IL-1 & IL-2

Question 9

• How might sensitisation result in chronic pruritus?

Answer 9

Peripheral sensitisation – scratching increases local inflammation, production of pruritogens by inflammatory cells, increased C-fibre response
Central sensitisation – inflammation of the skin alters the perception of gentle mechanical/other stimuli, perceived as pruritus

Question 10

• What are some of the sources of pruritus?

Answer 10

Allergic concentrations, environmental factors, ectoparasites, stress factors

Question 11

• What are some of the therapeutic approaches to pruritus?

Answer 11

Reduction of skin inflammation, blockage of peripheral inflammatory mediators, moisturisers, topical cooling preparations

Question 12

• List some of the possible causes of damage to the skin

Answer 12

Microbial, ectoparasitic, traumatic, chemical, auto-immune, allergic, endocrine, metabolic, nutritional & environmental

Question 13

• What are the epidermal responses?

Answer 13

Hyperkeratosis (scale & follicular hyperkeratosis), acanthosis, lichenification, vesicle/pustule formation, hyperpigmentation/hypopigmentation & crusting

Question 14

• What is hyperkeratosis?

Answer 14

Increases depth of the cornified layer

Question 15

• What is the difference between scaling and crusting?

Answer 15

Scaling is the production of abnormal or excessive scale, crusting is the formation of dried exudate

Question 16

• What is non-specific secondary keratosis a sign of?

Answer 16

Indicative of increased turnover of epidermis, or imbalance between turnover and desquamation

Question 17

• What is follicular hyperkeratosis?

Answer 17

When keratinaceous collars form around emerging hairs – follicular casts

Question 18

• What is the difference between acanthosis and hyperkeratosis?

Answer 18

Acanthosis is increased depth of epidermis, hyperkeratosis is increased depth of cornified layer

Question 19

• What is lichenification?

Answer 19

Thickening and hardening of the skin

Question 20

• What is the difference between a vesicle and a pustule?

Answer 20

Vesicle is filled with clear fluid, pustule is filled with pus – both are usually associated with infection

Question 21

• Which cells are responsible for hyperpigmentation & hypopigmentation?

Answer 21

Melanocytes in basal layer of epidermis

Question 22

• What are the main causes of crusting?

Answer 22

Multiple exudative and ulcerative diseases including physical damage, infectious processes, sterile inflammatory diseases & ulcerating neoplasms

Question 23

• What are the dermal responses?

Answer 23

Erythema, oedema & thickening

Question 24

• What causes erythema?

Answer 24

Release of pro-inflammatory mediators causing vasodilation of dermal vessels

Question 25

• What causes oedema?

Answer 25

Histamine and other cytokines increase vascular permeability causing leakage of tissue fluid

Question 26

• What is dermal thickening associated with?

Answer 26

Longer-standing allergic reactions & chronic inflammatory conditions

Question 27

• What is alopecia due to?

Answer 27

Failure of hair to grow properly or damage to hair follicles/shafts

Question 28

• List some of the additional diagnostic tests that can be used to diagnose skin diseases?

Answer 28

Skin scrapes, trichograms, cytology, FNA, biopsy, microbial culture, Wood’s lamp examination