Define pruritus
Unpleasant sensation that provokes the desire to scratch
What are the three mechanisms of pruritus?
- chemical mediators (histamine, prostaglandin, IL12)
- nerve transmission by unmyelinated fibres
- CNS mediators (opiates)
Name some mast cell degranulation stimuli
- Codeine
- Anti-IgE
- Allergen
- C5a
- Stem cell factor
Name some mast cell degranulation mediators
- Histamine
- Heparin
- Prostaglandin
- Cytokines
- Leukotrienes
- Platelet Activating Factor
What are the four main causes of itch?
- pruritoceptive
- neuropathic
- neurogenic
- psychogenic
Describe a pruritoceptive cause of itch
something in skin triggers the itch - inflammation/dryness
e.g. eczema, insect bite reactions, lichen planus
Describe a neuropathic cause of itch
damage to central or peripheral nerves
Describe a neurogenic cause of itch
No evident damage in CNS but itch caused by something acting on CNS e.g. opiates. Associated with systemic diseases.
What systemic diseases contribute to a neurogenic cause of an itch?
Paraneoplastic syndrome, haematological disease, kidney/thyroid disease
Describe the psychogenic cause of itch
Psychological causes, no CNS damage e.g delusions
How is an itch managed?
Find and treat the cause.
- anti-histamines
- emollients
- antidepressants
- phototherapy
- opiate antagonist
