Pruritus(Itch) Flashcards
what is the definition of an itch
usually unpleasant, poorly localised, non-adapting sensation that provokes the desire to scratch
when does the term pruritus tend to be used
tends to be used to refer to generalised itch without a cause primarily within the skin
where is the itch sensation processed in the brain
parts of the forebrain, and maybe hypothalamus
what chemical mediators of the skin are involved in the mediation of an itch
histamine, PGE2, acetylcholine, serotonin, kallikrein, IL2
what is the nerve transmission involved in mediation of an itch
unmyelinated C fibres
what CNS mediators are involved in the mediation of itch
opiates(exogenous and endogenous)
what role do mast cells have in itch mediation
mast cell degranulation releases chemical mediators of itch(eg histamine)
describe what a pruritoceptive cause of an itch is
something in skin that causes itch(usually inflammation or dryness)
describe what a neuropathic cause of an itch is
damage of any sort to central or peripheral nerves causing itch
describe what a neurogenic cause of an itch is
no evident damage in CNS, but itch caused
eg opiate effects of CNS
describe what a psychogenic cause of an itch is
psychological causes with no(currently detectable) CNS damage
eg itch delusions of infestation
describe what a combination pruritoceptive and neurogenic itch is
a patient with generalised itch due to central effect of endogenous opioids secondary to small bile duct obstruction and who is dermographic
give some examples of causes of pruritoceptive itch
asteatotic eczema, insect bite reactions, lichen planus, psoriasis
why does itching/scratching skin result in skin becoming dermographic
causes excessive mast cell degranulation and release of histamine and other within-skin mediators
give some examples of systemic disease that can be associated with neurogenic itch
liver and bile duct disease(eg primary biliary cirrhosis), kidney disease, thyroid disease, psychogenic
