Synonym: pruritus

Itch has many similarities to pain. They are both unpleasant sensory experiences, but pain elicits a reflex withdrawal and itch leads to a scratch reflex. However, both can lead to serious impairment of quality of life. Pruritus is defined as the desire to scratch. It can be peripheral, due to stimuli occurring in the skin, or central, when itching is perceived as occurring in the skin although it originates in the central nervous system.¹ Itching may be associated with skin disease or have a systemic cause.²

Presentation

• This will depend on the underlying cause.
• Although itching is common and the vast majority of cases have an obvious and benign cause, it is essential to consider possible less common but serious causes.³ Examination should therefore include careful assessment of the abdomen and lymph nodes.
• Examination of the skin in the itchy patient can help to elucidate the aetiology of the itch. A thorough examination may reveal lesions that the patient has not altered by scratching and therefore help in the diagnosis.

Differential diagnosis

Skin causes

• Contact dermatitis.
• Urticaria.
• Skin infestations: scabies, other pediculoses, insect bites.
• Atopic eczema.
• Pityriasis rosea.
• Psoriasis.
• Dermatitis herpetiformis.
• Lichen planus.
• Senile atrophy.
• Prickly heat.

Systemic causes

• Hepatic: cholestasis, especially primary biliary cirrhosis and drug-induced cholestasis.⁴
• Pregnancy.
• Endocrine: diabetes mellitus, thyrotoxicosis, hypothyroidism, hyperparathyroidism.
• Renal: chronic renal failure.
• Haematological: polycythaemia vera rubra, iron deficiency, leukaemia, myeloproliferative disorders.
• Malignancy: Hodgkin's disease, carcinoma (especially of the lung, prostate or stomach).
• Drug allergies or side-effects (e.g. opioid analgesics).
• Psychological: obsessive states, schizophrenia, dermatitis artefacta.

Investigations

Any suspicion of systemic cause, lack of obvious cause for itching or any patient with pruritus that does not respond to conservative therapy should be evaluated for underlying systemic disease.

• FBC, ESR, serum ferritin: iron deficiency anaemia, polycythaemia, raised eosinophils in allergy. Raised white cell count in leukaemia and raised ESR in malignancy.
• Fasting blood glucose.
• LFTs.
• Renal function and electrolytes.
• Calcium, phosphate, alkaline phosphatase.
• TFTs: hypothyroidism or hyperthyroidism.

Management

• The treatment of pruritus is aimed at identifying and treating the underlying cause as well as symptomatic treatment for the itch.
• Symptomatic treatment is primarily aimed at keeping the skin moist and cool.

General measures⁵

• Advise the patient to avoid scratching the skin and to keep their fingernails short. Wearing gloves at night and tapping the skin or drumming the fingers on the skin rather than scratching may be helpful.
• Cooling: simple measures to create a cooler environment, such as wearing light clothing and keeping cool in bed, may help. Avoid use of vasodilators (caffeine, alcohol, spices, hot water) and excessive sweating.
• Vibration: in localised pruritus the use of transcutaneous electrical nerve stimulation (TENS) may help in the short term.
• Acupuncture: may be of benefit in localised pruritus.
• Phototherapy: particularly ultraviolet B (UVB) and topical psoralen combined with UVA (PUVA) therapy; these have been shown to be of benefit in uraemic pruritus and urticaria pigmentosa.

Pharmacological

• Simple emollients may be effective when itching is associated with dry skin or in otherwise healthy elderly people.
• Preparations containing crotamiton are sometimes used but are of uncertain value.⁵
• Oral colestyramine is the treatment of choice for pruritus due to biliary obstruction but its effect may be temporary and it is only effective if biliary obstruction is incomplete.⁶
• Topical antihistamines and local anaesthetics are only marginally effective and may occasionally cause sensitisation.
• Oral antihistamines may be effective, but mainly in urticaria and insect bites. They are ineffective in most dermatoses and systemic causes. Sedating antihistamines may be useful for night-time use.
• Other drug treatments for itch include rifampicin, colestyramine and 17-alpha alkyl androgens (cholestasis), thalidomide (uraemia), cimetidine and corticosteroids (Hodgkin's lymphoma), paroxetine (paraneoplastic itch), aspirin and paroxetine (polycythaemia vera) and indometacin (some HIV-positive patients).⁷
• If these specific remedies fail, paroxetine and mirtazapine can be effective.
• UVB therapy may be more effective than drug treatment for itch in uraemia.
• Topical or systemic application of specific agonists such as cannabinoids or calcineurin inhibitors can influence neuroreceptors on sensory nerve fibres of the skin and suppress pruritus.⁸
• Itch-selective neurons in the dorsal horn of the spinal cord can be targeted to inhibit the transmission of pruritus to the somatosensory cortex. Anticonvulsants, antidepressants and micro-opioid receptor antagonists interfere with the sensation of pruritus in the central nervous system.

Complications

• Itch is a distressing, subjective symptom that may interfere significantly with the quality of a patient's life.

Document references

1. Greaves MW, Khalifa N; Itch: more than skin deep. Int Arch Allergy Immunol. 2004 Oct;135(2):166-72. Epub 2004 Sep 16. [abstract]
2. Pruritus, American Family Physician, 2003
3. Hiramanek N; Itch: a symptom of occult disease. Aust Fam Physician. 2004 Jul;33(7):495-9. [abstract]
4. Bosonnet L; Pruritis: scratching the surface; Eur J Cancer Care (Engl). 2003 Jun;12(2):162-5. [abstract]
5. Itch - widespread, Prodigy (February 2010)
6. Bergasa NV; Treatment of the Pruritus of Cholestasis. Curr Treat Options Gastroenterol. 2004 Dec;7(6):501-508. [abstract]
7. Twycross R, Greaves MW, Handwerker H, et al; Itch: scratching more than the surface. QJM. 2003 Jan;96(1):7-26. [abstract]
8. Pogatzki-Zahn E, Marziniak M, Schneider G, et al; Chronic pruritus: targets, mechanisms and future therapies. Drug News Perspect. 2008 Dec;21(10):541-51. [abstract]

Internet and further reading

• Yosipovitch G, Greaves MW, Schmelz M; Itch. Lancet. 2003 Feb 22;361(9358):690-4. [abstract]
• Cowdell F; Care and management of patients with pruritus. Nurs Older People. 2009 Sep;21(7):35-41. [abstract]