Pruritus Flashcards
Define pruritus
A usually unpleasant, poorly localised, non-adapting sensation that provokes the desire to scratch (i.e. itch)
Tends to refer to a generalised itch rather than localised
Describe the mechanism of pruritus
- Unmyelinated C fibres originating in the skin subserve (further/promote) Itch sensation and pain. Info on both itch and pain is then conveyed in two separate systems that both use the lateral spinothalamic tract.
- Itch sensation is then processed in parts of forebrain and hypothalamus
What are the different mediators of itch?
i.e. what they travel along, their chemical and CNS mediators
- Chemical mediators causing itch - e.g. Histamine, PGE2, acetylcholine, serotonin, kallikrein, IL-2, substance P tryptase, etc
- Nerve transmission: unmyelinated C fibres
- CNS mediators: opiates (endogenous and exogenous)
Appreciate some of the stimuli of mast cell degranulation
Appreciate some of the mediators released by mast cell degranulation
Define what is meant by a pruritoceptive cause of pruritus (itch)
Pruritoceptive - something (usually associated with inflammation or dryness) in skin that triggers itch
Define what is meant by a neuropathic cause of pruritus (itch)
Neuropathic - damage of any sort to central or peripheral nerves causing itch
Define what is meant by a neurogenic cause of pruritus (itch)
Neurogenic - no evident damage in CNS, but itch caused by, e.g., opiate effects on CNS receptors
Define what is meant by a psychogenic cause of pruritus (itch)
Psychogenic - psychological causes with no (currently detectable) CNS damage, e.g. itch in delusions of infestation
What type of nerve fibres does itch sensation travel across ?
Unmyelinated C fibres
What tract is info on itch sensation conveyed in ?
Spinthalamic tract
Give some examples of the systemic diseases associated with itch and what type of pruritus are they generally defined as ?
Most but not all neurogenic pruritus
Some of the systemic diseases associated with pruritus:
- Haematological
- Paraneoplastic
- Liver and bile duct e.g. primary billary cirrhosis
- Psychogenic
- Kidney disease
- Thyroid disease
What are the main points of the management of pruritus
Determine and treat the cause if possible
Anti-itch treatments:
- Sedative anti-histamines (non-sedative only useful if excess histamine in the skin i.e. urticaria & insect bites)
- Antidepressants, e.g. doxepin
- Opiate antagonists, e.g. ondansetron (a serotonin antagonist)
- Phototherapy
- Anti-eplieptics