Pruritus

Question 1

Define pruritus

Answer 1

Unpleasant sensation that provokes the desire to scratch

Question 2

What are the three mechanisms of pruritus?

Answer 2

• chemical mediators (histamine, prostaglandin, IL12)
• nerve transmission by unmyelinated fibres
• CNS mediators (opiates)

Question 3

Name some mast cell degranulation stimuli

Answer 3

• Codeine
• Anti-IgE
• Allergen
• C5a
• Stem cell factor

Question 4

Name some mast cell degranulation mediators

Answer 4

• Histamine
• Heparin
• Prostaglandin
• Cytokines
• Leukotrienes
• Platelet Activating Factor

Question 5

What are the four main causes of itch?

Answer 5

• pruritoceptive
• neuropathic
• neurogenic
• psychogenic

Question 6

Describe a pruritoceptive cause of itch

Answer 6

something in skin triggers the itch - inflammation/dryness

e.g. eczema, insect bite reactions, lichen planus

Question 7

Describe a neuropathic cause of itch

Answer 7

damage to central or peripheral nerves

Question 8

Describe a neurogenic cause of itch

Answer 8

No evident damage in CNS but itch caused by something acting on CNS e.g. opiates. Associated with systemic diseases.

Question 9

What systemic diseases contribute to a neurogenic cause of an itch?

Answer 9

Paraneoplastic syndrome, haematological disease, kidney/thyroid disease

Question 10

Describe the psychogenic cause of itch

Answer 10

Psychological causes, no CNS damage e.g delusions

Question 11

How is an itch managed?

Answer 11

Find and treat the cause.

• anti-histamines
• emollients
• antidepressants
• phototherapy
• opiate antagonist