Pruritus

Question 1

What is pruritus

Answer 1

Itch - A usually unpleasant, poorly localised, non-adapting sensation that provokes the desire to scratch

Question 2

What are the 3 subtypes of mediators of itch

Answer 2

Chemical mediators of skin e.g. histamine, IL2
Nerve transmission - unmyelinated (pruriceptive) C fibres
CNS mediators e.g. opiates

Question 3

Where is an itch processed in the brain

Answer 3

Forebrain & hypothalamus

Question 4

Name & describe the 4 causes of itch

Answer 4

• Pruritoceptive: something, usually inflammation or dryness, coming from within the skin triggers itch. Can include mast cells & unmyelinated C fibres
• Neuropathic: damage to central or peripheral nerves triggers itch (e.g. MS, shingles)
• Neurogenic: no evident damage in CNS, but itch mediated by CNS. It usually involves endogenous (PBC) or exogenous opiates
• Psychogenic: psychological causes with no CNS damage e.g. itch in delusions of infestation

=> usually multifactorial!

Question 5

Why do opiates cause itch

Answer 5

• CNS effects &
• Codeine induced mast cell degranulation

Question 6

Name 6 systemic diseases associated with itch

Answer 6

Haematological
paraneoplastic
Liver & bile duct disease/ obstruction
Psychogenic
Kidney disease
Thyroid disease

=> usually neurogenic itch

Question 7

Pruritus treatment

Answer 7

• Determine and treat cause if possible
• Anti-itch treatments (non-specific)
  
  • Sedative anti-histamines
  • Emollients (with menthol, or cooled in fridge)
  • Antidepressants
  • Phototherapy
  • Opiate antagonists, serotonin antagonists etc.
  • anti-epileptics for some neuropathic itches