Pruritus

Question 1

What is pruritic?

Answer 1

A usually unpleasant, poorly localised, non-adapting sensation that provokes the desire to scratch, tends to be used describe a generalised itch without a cause (primarily within the skin)

Question 2

Where is the sensation of pruritic processed in the brain?

Answer 2

Parts of the forebrain and possibly the hypothalamus

Question 3

What are some chemical mediators of itching in the skin?

Answer 3

Histamine, PGE2, acetylcholine, serotonin, kallikrein, IL-2, substance P tryptase

Question 4

What nerves are involved in the transmission of the itch sensation?

Answer 4

Unmyelinated C fibres (different ones transmit itch and temperature from those that transmit pain)

Question 5

What are the CNS mediators of itching?

Answer 5

Opiates (exogenous and endogenous)

Question 6

What are some mediators of itching released by mast cells?

Answer 6

Proteases, heparin, histamine, cytokines, prostaglandin D2, leukotriene C4/D4/E4, platelet activating factor

Question 7

What are the causes of itching?

Answer 7

Pruritoceptive, Neuropathic, Neurogenic, Psychogenic

Question 8

What causes pruritoceptive itching?

Answer 8

Something (usually associated with inflammation or dryness) in the skin that triggers an itch

Question 9

What causes neuropathic itching?

Answer 9

Damage of any sort to central/peripheral nerves

Question 10

What causes neurogenic itching?

Answer 10

No evident damage in CNS, but itch caused (e.g by opiate effects on CNS receptors)

Question 11

What causes psychogenic itching?

Answer 11

Psychological causes with no (currently detectable) CNS damage

Question 12

What are some examples of pruritoceptive itch?

Answer 12

Asteatotic eczema, insect bite reactions, lichen planus

Question 13

What is asteatotic eczema?

Answer 13

Direct exposure of itch, associated unmyelinated C fibres in bases of microfissures and inflammation with release of mediators in skin

Question 14

What virus is lichen planus associated with?

Answer 14

Hepatitis C (which causes a neurogenic itch)

Question 15

What are some systemic diseases that cause itching, and what type of itch do they mostly cause?

Answer 15

Haematological, paraneoplastic, liver/bile duct (primary biliary cirrhosis), psychogenic, kidney disease, thyroid disease; neurogenic itch

Question 16

What are some anti-itch treatments?

Answer 16

Sedative antihistamines (non-sedatives useless for most itch except where excess histamine is part of mechanism), emollients (with menthol or cooled in fridge), antidepressants (doxepine, SSRIs), phototherapy, opiate antagonists, ondansetron (serotonin anatagonist)