Pruritus Flashcards
What is the definition of pruritus?
A usually unpleasant, poorly localised, non-adapting sensation that provokes the desire to scratch
Where can scabies mites usually be found in the skin?
Present in the keratin layer
Where is the itch sensation processed in the brain?
In parts of the forebrain and hypothalamus
What chemical mediators ae involved in itch?
Histamine, PGE2, ACh, serotonin, kallikrein, IL-2, substance P tyryptase
What nerve transmission is involved in itch?
Unmyelinated C fibres
What CNS mediators are involved in itch?
Opiates (endogenous and exogenous)
What are the different types of mast cell degranulating stimuli?
Allergen
Substance P
Stem cell factor
Coedine
What mediators are released by dermal mast cell degranulation?
Tryptase, heparin, histamine
Prostaglanding D2, leukotrines, platelet-activating factor, cytokines (IL-3, 4, 5, 6, 8, 13), TNF-alpha
What are the 4 different types of itch?
Pruritoceptive
Neuropathic
Neurogenic
Psychogenic
What is a pruritoceptive itch?
Something (usually associated with inflammation or dryness) in skin that triggers itch
What is a neuropathic itch?
Damage of any sort to central or peripheral nerves causing itch
What is a neurogenic itch?
No evident damage of CNS, but itch caused by e.g. opiate effects on CNS receptors
What is a psychogenic itch?
Psychologial causes with no (currently detectable) CNS damage e.g. itch in delusions of infestation
What liver disease can lichen planus be associated with?
Hepatiitc C infection (causes neogenic itch)
What systemic diseases can be associated with an itch?
Heamatological Paraneoplastic Liver and bile duct Psychogenic Kidney disease Thyroid disease
