Pruritus Flashcards

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1
Q

Definition of itch

A

A usually unpleasant, poorly localised, non-adapting sensation that provokes the desire to scratch

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2
Q

True or false: information on itch and pain is conveyed centrally in the same system

A

False - information in itch and pain is conveyed centrally in 2 separate systems

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3
Q

Which tract do both itch and pain systems use?

A

Lateral spinothalamic tract

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4
Q

Where is itch sensation processed?

A

Parts of the forebrain

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5
Q

Things that mediate itch

A

Chemical mediators in skin
Nerve transmission
CNS mediators

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6
Q

Chemical mediators of itch

A
Histamine
PGE2
Acetylcholine
Serotonin
Kallikrein
IL-2
Substance P tryptase
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7
Q

Example of CNS mediator of itch

A

Opiates

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8
Q

What may itch be caused by?

A

Too many mast cells or mast cells degranulating more than usual

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9
Q

Types of causes of itch

A
Pruritoceptive
Neuropathic
Neurogenic
Psychogenic
Multifactorial
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10
Q

Pruritoceptive cause of itch:

  • What is it?
  • Examples
A

Something (usually associated with inflammation or dryness in the skin) triggers itch
Examples - asteototic eczema, insect bites, lichen planus, psoriasis

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11
Q

Neuropathic cause of itch:

  • What is it?
  • Examples
A

Damage to any sort of central or peripheral nerves causing itch
Examples - after shingles, in multiple sclerosis

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12
Q

Neurogenic cause of itch

A

No evident damage in CNS but itch caused by e.g. opiate effects on CNS receptors. Mediated by CNS

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13
Q

Psychogenic cause of itch:

  • What is it?
  • Example
A

Psychological causes with no (currently detectable) CNS damage
Example - itch in the delusions of infestation

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14
Q

Systemic diseases associated with itch (mostly neurogenic)

A
Haematological
Paraneoplastic
Liver and bile duct
Psychogenic
Kidney disease
Thyroid disease
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15
Q

Management of itch

A

Determine the cause if possible
Treat the cause
Anti-itch treatments

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16
Q

Which type of itch is generally easiest to treat?

A

Pruritoceptive due to inflammatory skin diseases

17
Q

Anti-itch treatments

A

Sedative anti-histamines
Emollients (with menthol or cooled in the fridge)
Antidepressants
Phototherapy
Opiate antagonists
Anti-epileptics for some types of neuropathic itch