Pruritis Flashcards
is pruritic localised?
no
poorly localised
where do mites live in a scabies infection?
in the keratin layer
what carries sensation of itch?
unmyelinated C nerve fibres go up into skin transmit sensation/temperature via spinothalmic tract to forebrain where it is processed
what 3 types of mediators mediate itching?
chemical - histamine, PGE2 etc
Nerve transmission - unmyelinated C fibres
CNS mediators - opiates (endogenous and exogenous)
what can cause mast cells to degranulate and release histamine etc causing an itch?
allergen (IgE) Autoimmune - IgG binding to IgE receptors substance P codeine (not allergic) stem cell factor …..……..
what pre-formed mediators are released by mast cells?
Pre-formed:
- histamine
- proteases
- heparin
what are the 4 categories of causes of itch?
pruritoceptive - something within the skin (inflammation or dryness)
neuropathic - damage to central/peripheral nerves (e.g MS)
neurogenic - no damage but itch caused by e.g opiate effects on CNS receptors
Psychogenic - No CNS damage, psychological cause (e.g delusions)
can categories of itch overlap?
yes
pruritoceptive and neurogenic itch - PBC causes neurogenic itch then the scratching causes the pruritoceptive itch
examples of pruritoceptive itch?
insect bite reaction lichen planus asteatotic eczema psoriasis prurigo nodularis
what is the koebner phenomenon seen in?
psoriasis
lichen planus
vitiligo
neurogenic itch examples?
most systemic diseases that are associated with an itch kidney disease liver/bile duct disease haematological paraneoplastic thyroid disease psychogenic
how high does bilirubin need to be before you see jaundice?
around 40
how is itching managed?
determine cause treat cause anti-itch treatments: - antihistamines - emollients - antidepressants - phototherapy - opiate antagonists - anti-epileptics for some neuropathic itches
what newly-formed mediators are released by mast cells?
proastaglandin D2
leukotrienes
platelet activating factor
do mast cells release cytokines?
yes
