Pruritus Flashcards

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1
Q

Define pruritus

A

A usually unpleasant, poorly localised, non-adapting sensation that provokes the desire to scratch (i.e. itch)

Tends to refer to a generalised itch rather than localised

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2
Q

Describe the mechanism of pruritus

A
  • Unmyelinated C fibres originating in the skin subserve (further/promote) Itch sensation and pain. Info on both itch and pain is then conveyed in two separate systems that both use the lateral spinothalamic tract.
  • Itch sensation is then processed in parts of forebrain and hypothalamus
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3
Q

What are the different mediators of itch?

i.e. what they travel along, their chemical and CNS mediators

A
  • Chemical mediators causing itch - e.g. Histamine, PGE2, acetylcholine, serotonin, kallikrein, IL-2, substance P tryptase, etc
  • Nerve transmission: unmyelinated C fibres
  • CNS mediators: opiates (endogenous and exogenous)
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4
Q

Appreciate some of the stimuli of mast cell degranulation

A
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5
Q

Appreciate some of the mediators released by mast cell degranulation

A
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6
Q

Define what is meant by a pruritoceptive cause of pruritus (itch)

A

Pruritoceptive - something (usually associated with inflammation or dryness) in skin that triggers itch

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7
Q

Define what is meant by a neuropathic cause of pruritus (itch)

A

Neuropathic - damage of any sort to central or peripheral nerves causing itch

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8
Q

Define what is meant by a neurogenic cause of pruritus (itch)

A

Neurogenic - no evident damage in CNS, but itch caused by, e.g., opiate effects on CNS receptors

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9
Q

Define what is meant by a psychogenic cause of pruritus (itch)

A

Psychogenic - psychological causes with no (currently detectable) CNS damage, e.g. itch in delusions of infestation

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10
Q

What type of nerve fibres does itch sensation travel across ?

A

Unmyelinated C fibres

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11
Q

What tract is info on itch sensation conveyed in ?

A

Spinthalamic tract

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12
Q

Give some examples of the systemic diseases associated with itch and what type of pruritus are they generally defined as ?

A

Most but not all neurogenic pruritus

Some of the systemic diseases associated with pruritus:

  • Haematological
  • Paraneoplastic
  • Liver and bile duct e.g. primary billary cirrhosis
  • Psychogenic
  • Kidney disease
  • Thyroid disease
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13
Q

What are the main points of the management of pruritus

A

Determine and treat the cause if possible

Anti-itch treatments:

  • Sedative anti-histamines (non-sedative only useful if excess histamine in the skin i.e. urticaria & insect bites)
  • Antidepressants, e.g. doxepin
  • Opiate antagonists, e.g. ondansetron (a serotonin antagonist)
  • Phototherapy
  • Anti-eplieptics
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