Derm. Misc. 4 - Pruritus

Question 1

What is pruritus?

Answer 1

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

Question 2

Difference between young and adult scabie mites?

Answer 2

Young mite = 6 legs

Adult = 8 legs

Question 3

Major steps in the mediation of an itch? (4)

Answer 3

Chemical mediators in the skin are released due to mast cell degranulation
This causes nerve transmission through C-fibres
Opiates in the CNS = mediators
Itch sensation is then processed in the forebrain and hypothalamus

Question 4

Examples of chemical pre-formed mediators released by mast cell degranulation? (4)

Answer 4

Proteases
Heparin
Histamine
Cytokines

Question 5

Examples of chemical newly-formed mediators released by mast cell degranulation? (4)

Answer 5

Prostaglandin D2
Leukotrienes C4, D4, E4
Platelet-activating factor
Cytokines

Question 6

Mast cell degranulating stimuli? (8)

Answer 6

Allergen
Anti-FceRI
IgE
anti-IgE
substance P
stem cell factor
C5alpha
codeine

Question 7

What are the names of the 4 causes of an itch?

Answer 7

Pruritoceptive
Neuropathic
Neurogenic
Psychogenic

Question 8

What is a pruritoceptive itch?

Answer 8

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

Question 9

What causes a neuropathic itch?

Answer 9

Damage of any sort to central or peripheral nerves causing itch

Question 10

When is an itch classed as neurogenic?

Answer 10

No evident damage in CNS, but itch caused by it e.g. opiate effects on CNS

Question 11

What is a psychogenic itch?

Answer 11

An itch with psychological causes with no (currently detectable) CNS damage

Question 12

Example of a psychogenic itch?

Answer 12

Itch in delusions of infestation

Question 13

What type of itch is a generalised itch due to central effect of endogenous opioids secondary to a small bile duct obstruction?

Answer 13

Pruritoceptive and neurogenic

Question 14

What type of itch is demorgraphism?

Answer 14

Pruritoceptive and neurogenic

Question 15

What is dermographism?

Answer 15

Excessive mast cell degranulation and histamine release caused by stroking the skin

Question 16

What type of itch is asteatotic eczema?

Answer 16

Pruritoceptive

Question 17

What is asteatotic eczema?

Answer 17

Skin is abnormally dry, itchy or cracked = direct exposure of itch-asossicated unmmyelinated C-fribres in bases of micro fissures and inflammation with release of mediators in skin

Question 18

What type of itch is insect bite reactions?

Answer 18

Pruritoceptive

Question 19

What type of itch is lichen planus?

Answer 19

Pruritoceptive

Question 20

What type of itch is psoriasis?

Answer 20

Pruritoceptive

Question 21

What type of itch is prurigo nodularis?

Answer 21

Pruritoceptive

Question 22

What type of itch is MS?

Answer 22

Neuropathic

Question 23

What type of itch is shingles?

Answer 23

Neuropathic

Question 24

What type of itch is caused by drugs such as opiates and tramadol?

Answer 24

Neurogenic

Question 25

What type of itch is caused by haematological conditions e.g. chronic iron deficiency?

Answer 25

Neurogenic

Question 26

What type of itch is caused by paraneoplastic syndrome?

Answer 26

Neurogenic

Question 27

What type of itch is caused by kidney disease?

Answer 27

Neurogenic

Question 28

What type of itch is caused by thyroid disease?

Answer 28

Neurogenic

Question 29

General management of pruritus? (3)

Answer 29

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

Question 30

Examples of anti-itch treatments?

Answer 30

Selective anti-histamines (useless for most itch except where excess histamine is part of mechanism)
Emollients (with menthol or cooled in fridge)
Anti-depressants
(for some types of neuropathic itch, anti-epileptics)
Phototherapy
Opiate antagonists
Odansetron (a serotonin antagonist)

Question 31

Anti-depressant useful for some itches

Answer 31

Doxepin