Pruritus Flashcards
Definition of itch
A usually unpleasant, poorly localised, non-adapting sensation that provokes the desire to scratch
True or false: information on itch and pain is conveyed centrally in the same system
False - information in itch and pain is conveyed centrally in 2 separate systems
Which tract do both itch and pain systems use?
Lateral spinothalamic tract
Where is itch sensation processed?
Parts of the forebrain
Things that mediate itch
Chemical mediators in skin
Nerve transmission
CNS mediators
Chemical mediators of itch
Histamine PGE2 Acetylcholine Serotonin Kallikrein IL-2 Substance P tryptase
Example of CNS mediator of itch
Opiates
What may itch be caused by?
Too many mast cells or mast cells degranulating more than usual
Types of causes of itch
Pruritoceptive Neuropathic Neurogenic Psychogenic Multifactorial
Pruritoceptive cause of itch:
- What is it?
- Examples
Something (usually associated with inflammation or dryness in the skin) triggers itch
Examples - asteototic eczema, insect bites, lichen planus, psoriasis
Neuropathic cause of itch:
- What is it?
- Examples
Damage to any sort of central or peripheral nerves causing itch
Examples - after shingles, in multiple sclerosis
Neurogenic cause of itch
No evident damage in CNS but itch caused by e.g. opiate effects on CNS receptors. Mediated by CNS
Psychogenic cause of itch:
- What is it?
- Example
Psychological causes with no (currently detectable) CNS damage
Example - itch in the delusions of infestation
Systemic diseases associated with itch (mostly neurogenic)
Haematological Paraneoplastic Liver and bile duct Psychogenic Kidney disease Thyroid disease
Management of itch
Determine the cause if possible
Treat the cause
Anti-itch treatments
