what is the definition of pruritus?
a usually unpleasant, poorly localised, non-adapting sensation that provokes the desire to scratch
how many legs does an adult scabies mite have?
8
where is the itch sensation processed in the brain?
the forebrain & the hypothalamus
name the 3 types of mediators of itch
- chemical mediators in the skin
- nerve transmission
- CNS mediators
give some examples of chemical mediators of itch in the skin
- histamine
- PGE2
- acetylcholine
- serotonin
- Il 2
- substance P tryptase
give an example of the nerves involved in mediating itch
unmyelinated C fibres
give an example of the CNS mediators
opiates
what are the 4 different types of causes of itch?
- prutitoceptive
- neuropathic
- neurogenic
- psychogenic
what is a pruritoceptive cause of itch?
something in the skin that triggers itch, usually assoc. with inflammation/dryness
what is a neuropathic cause of itch?
damage of any sort to central or peripheral nerves causing itch
what is a neurogenic cause of itch?
no evident damage in CNS but itch caused by e.g. opiate effects on CNS receptors
what is a psychogenic cause of itch?
psychological causes with no (currently detectable) CNS damage e.g. itch in delusions of infestations
name some systemic diseases assoc. with itch
mostly, not all, neurogenic itch:
- haemotological
- paraneoplastic
- liver & bile duct
- psychogenic
- kidney disease
- thyroid disease
how is itch managed?
- treat the cause
- anti-itch treatments
name some anti-itch treatments
- sedative anti-histamines
- emollients
- anti-depressants
- phototherapy
- opiate antagonists
- for some types of neuropathic itch, anti-epileptics
