Pruritus Flashcards
What is pruritus?
An unpleasant, poorly localised, non-adapting sensation that provokes the desire to scratch
Where on the the body do we experience pruritus?
Predominantly the skin but also conjunctiva and/or mucous membranes
How does the sensation of itch occur?
Unmyelinated C fibres subserving the itch sensation originate in the skin > sensations are conveyed into the lateral spinothalamic tract > sensation is processed in parts of the forebrain and hypothalamus
What are the chemical mediators of itch in the skin?
Histamine, PGE2, acetylcholine, serotonin, IL-2, substance P, tryptase, kallikrein, etc
The same nerve fibres which transmit itch also transmit pain and temperature. T/F
False - different fibres transmit pain
What are the CNS mediators of itch?
Endogenous and exogenous opiates
List some stimuli which cause the degranulation of mast cells
Allergens, anti-IgE, substance P, stem cell factor, codeine, C5a (complement), etc
Mast cell degranulation causes the release of chemicals which cause itch. T/F
True
What are the causes of itch?
Pruritoceptive, neuropathic, neurogenic, psychogenic
What is pruritoceptive itch?
Something within the skin causes itch (dryness, inflammation, etc)
What is neuropathic itch?
Damage to central or peripheral nerves causing itch
What is neurogenic itch?
Itch caused by stimulation of CNS nerves with no evident damage to said nerves (e.g opiates)
What is psychogenic itch?
Psychological causes without (detectable) CNS damage
What is dermographic urticaria? What type of itch does this cause?
Urticarial rash occurs where the skin is stroked/scratched due to mast cell degranulation. Pruritoceptive
A patient with itch due to liver disease has which type of itch?
Neurogenic
What is xerotic/asteatotic eczema? What type of itch does this cause and how?
Eczema caused by dry skin. Pruritoceptive. Unmyelinated C fibres are directly exposed (in the bases of skin microfissures) to inflammatory mediators released in the skin
What type of itch is caused by insect bite reactions?
Pruritoceptive
What is lichen planus? What type of itch does it cause?
A lichen-like disease of the skin/mucous membranes with an unknown aetiology. Pruritoceptive
What other itchy condition is lichen planus associated with? What type of itch does this cause?
Hep C infection. Neurogenic
Which systemic diseases are associated with itch? What type of itch is most commonly associated with these?
Haematological, paraneoplastic, liver & bile duct, kidney disease, thyroid disease. Neurogenic
How can itch be managed?
Treat underlying cause, sedative anti-histamines, emollients (with menthol or cooled), antidepressants (doxipin & SSRIs), phototherapy, opiate antagonists, ondansetron (serotonin antagonist), anti-epileptics (specific neurogenic itch)
