Pruritis Flashcards

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1
Q

is pruritic localised?

A

no

poorly localised

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2
Q

where do mites live in a scabies infection?

A

in the keratin layer

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3
Q

what carries sensation of itch?

A

unmyelinated C nerve fibres go up into skin transmit sensation/temperature via spinothalmic tract to forebrain where it is processed

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4
Q

what 3 types of mediators mediate itching?

A

chemical - histamine, PGE2 etc
Nerve transmission - unmyelinated C fibres
CNS mediators - opiates (endogenous and exogenous)

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5
Q

what can cause mast cells to degranulate and release histamine etc causing an itch?

A
allergen (IgE)
Autoimmune - IgG binding to IgE receptors
substance P
codeine (not allergic)
stem cell factor
…..……..
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6
Q

what pre-formed mediators are released by mast cells?

A

Pre-formed:

  • histamine
  • proteases
  • heparin
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7
Q

what are the 4 categories of causes of itch?

A

pruritoceptive - something within the skin (inflammation or dryness)
neuropathic - damage to central/peripheral nerves (e.g MS)
neurogenic - no damage but itch caused by e.g opiate effects on CNS receptors
Psychogenic - No CNS damage, psychological cause (e.g delusions)

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8
Q

can categories of itch overlap?

A

yes

pruritoceptive and neurogenic itch - PBC causes neurogenic itch then the scratching causes the pruritoceptive itch

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9
Q

examples of pruritoceptive itch?

A
insect bite reaction
lichen planus
asteatotic eczema
psoriasis
prurigo nodularis
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10
Q

what is the koebner phenomenon seen in?

A

psoriasis
lichen planus
vitiligo

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11
Q

neurogenic itch examples?

A
most systemic diseases that are associated with an itch
kidney disease
liver/bile duct disease
haematological
paraneoplastic
thyroid disease
psychogenic
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12
Q

how high does bilirubin need to be before you see jaundice?

A

around 40

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13
Q

how is itching managed?

A
determine cause
treat cause
anti-itch treatments:
- antihistamines
- emollients
- antidepressants
- phototherapy
- opiate antagonists
- anti-epileptics for some neuropathic itches
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14
Q

what newly-formed mediators are released by mast cells?

A

proastaglandin D2
leukotrienes
platelet activating factor

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15
Q

do mast cells release cytokines?

A

yes

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16
Q

what is prurigo nodularis?

A

small itchy nodules secondary to chronic itch (e.g from renal failure, PBC etc)