6: Mechanisms of pruritus Flashcards
What is pruritus?
Unpleasant, poorly localised sensation that makes you want to scratch
What is a possible advantage of pruritus and subsequent scratching?
Removal of parasites e.g scabies
Which parts of the brain are thought to be responsible for pruritus?
Forebrain
Hypothalamus
Name a chemical mediator for pruritus.
Histamine
amongst many others
Apart from histamine, what other types of signal can trigger pruritus?
Nerve transmission
CNS mediators (i.e opiates)
Which immune cells contain histamine and are triggered to degranulate by IgE (in complexes with allergens) and IgG?
Mast cells
Apart from histamine, what else do mast cells contain?
Heparin
Proteases
Prostaglandins
Leukotrienes
Which immune cells look similar to mast cells and share some of the same functions?
Basophils
What are the four general causes of itch?
Pruritoceptive
Neuropathic
Neurogenic
Psychogenic
What causes a pruritoceptive itch?
Something pathogenic in the skin e.g inflammation / dryness
What causes a neuropathic itch?
Damage to central or peripheral nerves
What causes a neurogenic itch?
CNS mediators e.g opiates
What causes a psychogenic itch?
Psychological issues e.g delusions of infestations
CRAWLING IN MY SKIIIIN
What is dermographism?
Minor stroking causes mast cell degranulation and an inflammatory rash
also known as “skin writing”
What is asteatotic eczema?
Where is it usually found?
What type of pruritus is it associated with?
Eczema due to dry skin
Shins
Pruritoceptive
Give two examples of pruritoceptive itches.
Asteatotic eczema
Insect bites
Dermographism
Lichen planus
Give two GI diseases which cause a neurogenic itch.
Primary biliary cirrhosis
Chronic hepatitis
What is the first thing that should be done in the treatment of pruritus?
Treat the underlying cause if you know what it is
What are some non-specific therapies a patient can try to resolve their pruritus?
Antihistamines
Emollients
Antidepressants
Phototherapy
Opiate antagonists
