Generalised pruritus

CAUSES:

• Uraemic pruritus
  • arises in patients undergoing dialysis is due to a combination of
    • xerosis (dry skin)
    • secondary hyperparathyroidism
    • peripheral neuropathy (nerve changes)
    • inflammation.
• Secondary hyperparathyroidism
  • also occurs in dialysis patients leads to microprecipitation (deposition) of calcium and magnesium salts in the skin, triggering mast cell degeneration, releasing serotonin and histamine.
  • Once chronic pruritus has occurred, there may be secondary changes in the nerves in the skin and central nervous system which heighten the sensation of itch.
• Hepatogenic pruritus
  • in intrahepatic than extrahepatic cholestasis.
    • chronic viral hepatitis
    • primary biliary cirrhosis
    • pregnancy-related cholestasis.
  • Extra-hepatic cholestasis is associated with pressure on the bile ducts
    • eg from pancreatic tumours or pseudocysts.
  • Cholestasis
    • is thought to release toxic substances from the liver, which stimulates neural itch fibres in the skin.
    • Characteristically, cholestatic pruritus is most severe at night; it tends to affect the hands, feet and areas where clothes are rubbing on the skin.

• Haematological disorders
  • iron deficiency anaemia
    • glossitis (tongue inflammation)
    • angular cheilitis (inflammation of mouth corners)
  • polycythaemia vera
    • the itch is usually precipitated by contact with water (aquagenic pruritus)
    • is thought to be mediated by the effect of platelets, serotonin and prostaglandins.

• Endocrine disorders include thyroid disease and diabetes mellitus.
  • Graves’ disease (thyrotoxicosis)
    • increased blood flow, skin temperature and decreased itch threshold mediated by the increase in thyroid hormones, lead to the itch. Pruritus associated with myxoedema and hypothyroidism is rare, and if present, is more likely the result of xerosis (dry skin).
  • diabetes mellitus
    • localised itch tends to occur in the perianal/genital region usually due to Candida albicans or dermatophyte infections. 
    • It is unclear if metabolic abnormalities such as renal impairment, autonomic failure or diabetic neuropathy contribute to this.

• Paraneoplastic itch
  • associated with lymphoma, especially
    • Hodgkin lymphoma
    • Leukaemia
    • solid organ tumour (eg lung, colon, brain).

• Infections
  • human immunodeficiency virus infection (HIV) 
  • hepatitis C virus.

History

1. nature
2. distribution of itching
3. drug history
4. associated general symptoms:  fever.

Key examination

• General examination of the skin, abdomen and lymphopoietic systems
• Examine for dermographism by firmly drawing a line in the patient’s skin with a tongue depressor and observe for an urticarial response

Key investigations to consider

• Urinalysis
• Pregnancy test
• FBE
• Iron studies
• Kidney function tests
• Liver function tests
• Thyroid function tests
• Random blood sugar
• Stool examination (ova and cysts)
• Chest X-ray
• Skin biopsy
• Allergy patch testing
• Lymph node biopsy (if present)
• Immunological tests for primary biliary cirrhosis (e.g. anti-mitochondrial antibodies)

Treatment

• The basic principle of treatment is to determine the cause of the itch and treat it accordingly. 
• Itch of psychogenic origin responds to appropriate therapy, such as amitriptyline for depression 
• If no cause is found:
  • apply cooling measures (e.g. air-conditioning, cool swims)
  • avoid rough clothes; wear light clothing, avoid known irritants , overheating
  • avoid vasodilatation (e.g. alcohol, hot baths/showers keep showers short and not too hot)
  • treat dry skin with appropriate moisturisers (e.g. propylene glycol in aqueous cream)
• topical treatment
  • emollients to lubricate skin
  • local soothing lotion such as calamine, including menthol or phenol (avoid topical antihistamines)
  • pine tar preparations (e.g. Pinetarsol)
  • crotamiton cream
  • consider topical corticosteroids
• sedative antihistamines (not very effective for systemic pruritus)
• non-sedating antihistamines during day
• antidepressants (e.g. doxepin) or tranquillisers (if psychological cause and counselling ineffective)
• phototherapy