Derm. Misc. 4 - Pruritus Flashcards
What is pruritus?
An unpleasant, poorly localised, non-adapting sensation that provokes the desire to scratch
Difference between young and adult scabie mites?
Young mite = 6 legs
Adult = 8 legs
Major steps in the mediation of an itch? (4)
Chemical mediators in the skin are released due to mast cell degranulation
This causes nerve transmission through C-fibres
Opiates in the CNS = mediators
Itch sensation is then processed in the forebrain and hypothalamus
Examples of chemical pre-formed mediators released by mast cell degranulation? (4)
Proteases
Heparin
Histamine
Cytokines
Examples of chemical newly-formed mediators released by mast cell degranulation? (4)
Prostaglandin D2
Leukotrienes C4, D4, E4
Platelet-activating factor
Cytokines
Mast cell degranulating stimuli? (8)
Allergen Anti-FceRI IgE anti-IgE substance P stem cell factor C5alpha codeine
What are the names of the 4 causes of an itch?
Pruritoceptive
Neuropathic
Neurogenic
Psychogenic
What is a pruritoceptive itch?
something (usually associated with inflammation or dryness) in the skin that triggers the itch
What causes a neuropathic itch?
Damage of any sort to central or peripheral nerves causing itch
When is an itch classed as neurogenic?
No evident damage in CNS, but itch caused by it e.g. opiate effects on CNS
What is a psychogenic itch?
An itch with psychological causes with no (currently detectable) CNS damage
Example of a psychogenic itch?
Itch in delusions of infestation
What type of itch is a generalised itch due to central effect of endogenous opioids secondary to a small bile duct obstruction?
Pruritoceptive and neurogenic
What type of itch is demorgraphism?
Pruritoceptive and neurogenic
What is dermographism?
Excessive mast cell degranulation and histamine release caused by stroking the skin
What type of itch is asteatotic eczema?
Pruritoceptive
What is asteatotic eczema?
Skin is abnormally dry, itchy or cracked = direct exposure of itch-asossicated unmmyelinated C-fribres in bases of micro fissures and inflammation with release of mediators in skin
What type of itch is insect bite reactions?
Pruritoceptive
What type of itch is lichen planus?
Pruritoceptive
What type of itch is psoriasis?
Pruritoceptive
What type of itch is prurigo nodularis?
Pruritoceptive
What type of itch is MS?
Neuropathic
What type of itch is shingles?
Neuropathic
What type of itch is caused by drugs such as opiates and tramadol?
Neurogenic
What type of itch is caused by haematological conditions e.g. chronic iron deficiency?
Neurogenic
What type of itch is caused by paraneoplastic syndrome?
Neurogenic
What type of itch is caused by kidney disease?
Neurogenic
What type of itch is caused by thyroid disease?
Neurogenic
General management of pruritus? (3)
Determine cause if possible
Treat cause if possible
Anti-itch treatments
Examples of anti-itch treatments?
Selective anti-histamines (useless for most itch except where excess histamine is part of mechanism)
Emollients (with menthol or cooled in fridge)
Anti-depressants
(for some types of neuropathic itch, anti-epileptics)
Phototherapy
Opiate antagonists
Odansetron (a serotonin antagonist)
Anti-depressant useful for some itches
Doxepin
