Pruritis Flashcards
What parts of the brain process the sensation of itching?
parts of forebrain and hypothalamus
What factors can mediate itch?
Chemical mediators in skin
Nerve transmission
Central nervous system mediators
Give examples of chemical mediators in the skin which induce itching
histamine PGE2 acetylcholine serotonin kallikrein interleukin 2 substance P tryptase
What type of nerve fibres mediate itch?
unmyelinated C fibres
different ones transmit itch and temperature from those that transmit pain
Give an example of CNS mediators which cause itch
opiates
What factors are responsible for degranulation of mast cells?
Anti IgE Allergens Substance P C5a Codeine
What mediators are released during dermal mast cell degranulation?
PRE-FORMED:
- Proteases
- Heparin
- Histamine
NEWLY FORMED:
- Prostaglandin D2
- Leukotrienes C4 D4 E4
- Platelet activating factorq
ALSO CYTOKINES
What are the four types of itch?
Pruritoceptive
Neuropathic
Neurogenic
Psychogenic
What is a pruritoceptive itch?
something in skin that triggers the itch
usually associated with inflammation or dryness
What is a neuropathic itch?
damage of any sort to central or peripheral nerves causing itch
What is neurogenic pain?
no evident damage in CNS, but itch caused by e.g. opiate effects on CNS receptors
What is psychogenic pain?
psychological causes with no (currently detectable) CNS damage e.g. itch in delusions of infestation
What systemic diseases are associated with itch?
Haematological Paraneoplastic Liver and bile duct Psychogenic Kidney disease Thyroid disease
What treatments can be used for anti-itching
Sedative anti-histamines Emollients Antidepressants anti-epileptics (for neuropathic itch) Phototherapy Opiate antagonists, ondansetron
