Itch

Question 1

Define pruritus

Answer 1

Itch (pruritus) definition = a usually unpleasant, poorly localised, non-adapting sensation that provokes the desire to scratch.

Question 2

What are the four groups of classification of itch?

Answer 2

1. Pruritoceptive: something (usually associated with inflammation or dryness) in skin that triggers itch
2. Neuropathic: damage of any sort to central or peripheral nerves causing itch
3. Neurogenic: no evident damage in CNS, but itch caused by, e.g., opiate effects on CNS receptors
4. Psychogenic: psychological causes with no (currently detectable) CNS damage, e.g. itch in delusions of infestation

Question 3

Which two types of itch tend to occur together?

Answer 3

Pruritoceptive and neurogenic itch: a patient with generalised itch due to central effect of endogenous opiods secondary to small bile duct obstruction (autoimmune disease – primary biliary cirrhosis) and who is dermographic (stroking skin causes excessive mast cell degranulation and release of histamine and other within-skin mediators).

Question 4

What are the treatment options for managing itch?

Answer 4

• Sedative anti-histamines (non-sedative antihistamines useless for most itch except where excess histamine in the skin is part of the mechanism)
• Emollients (with menthol, or cooled in fridge – counter-irritant effects)
• Antidepressants, e.g. doxepin and some of the newer ones including SSRIs
• (For some types of neuropathic itch, anti-epileptics)
• Phototherapy
• Opiate antagonists, ondansetron (a serotonin antagonist), etc