Shared article

Itch

"An unpleasant sensation that provokes the desire to scratch"

Overview of the article

  • Causes of itch
  • Relevant history and examination
  • Further investigations
  • Management
  • The mechanism and physiology of itch
  • Take home message
  • Useful references

Causes

History

Further questions to ask:

  • Worse at night + others affected - Scabies
  • Worsened by a hot bath - Polycythaemia
  • Recent exposure to animals/plants
  • Exposure to new chemicals
  • Associated with weals - urticaria

 

Past medical history:

  • Diabetes
  • Liver disease 
  • Thyroid disease

 

Drug history

  • Morphine/other opiates
  • Chloroquine

Examination

Further investigations

Blood tests

  • Full blood count
  • Urea and electrolytes
  • Erythrocyte Sedimantation Rate
  • Glucose (random/fasting)
  • Liver function tests
  • Ferrritin
  • Thyroid function tests

Management

Manage underlying condition

Topicals (First-line: Aimed at restoring and preserving the skin's barrier function)

  1. Emollients
  2. Low pH cleansers and moisterizer: Preserves normal acidic condition of the skin. High pH has been noted in xerosis, uraemia and dermatitis
  3. Antihistamines: Blocks H1 receptors; useful for urticaria and insect bites
  4. Corticosteroids: Indirect relief of itch through its anti-inflammatory properties. Side effects need to be considered.
  5. Capsaicin: Useful for intractable pruritus at localised site. This desensitizes fibers associated with pain and itch
  6. Anaesthetics: EMLA (Eutectic Mixture of Local Anaesthetics) is useful for mild to moderate pruritus

Additional notes: The mechanism and physiology of pruritus

*This section is by no means essential for exam revision, but it makes things more interesting!*

 

The sensation of itchiness is transmitted through unmyelinated C-polymodal fibers, with free nerve endings on the skin surface. These neurons may be sensitive to pruritogenic substances and lie more superficially than pain fibers. Triggers include histamine, neuropeptide substance P, bradykinin, serotonin and endothelin. Stimulation of opioid mu receptors accentuates pain, and suppression has the opposite effect. From the peripheral receptors, the sensation is transmitted to the dorsal root ganglion to the spinothalamic tract.

 

Individuals with congenital loss of sensitivity to pain also loses sensitivity to itch.

Take home message

1. Important questions to ask:

  • Factors that worsen the itch
  • Occupation/recent exposure
  • Associated features (jaundice, weight loss)

 

2. Remember to take a detailed past medical history (diabetes milletus; thyroid disease) and drug history

3. Rule out sinister pathology (haematological malignancies; organ failure)

4. Carry out a thorough examination of relevant systems which may contribute towards the symptoms

5. Itch, in finals exams, is commonly raised in context with the following conditions:

  • Dermatological conditions (scabies, psoriasis)
  • Renal failure
  • Liver disease

 

Useful References

http://www.iasp-pain.org/AM/Template.cfm?Section=Home&Template=/CM/ContentDisplay.cfm&ContentID=2200

http://www.medscape.com/viewarticle/488914_4

http://emedicine.medscape.com/article/1098029-overview

 

Advertisement

Fastbleep © 2019.