An irritating sensation that compels the patient to scratch. It can lead to an itch-scratch-itch cycle and lichenification.
Commonly without a definite cause. Likely cause if any depends on location of itch! A general guide for diagnosis is to distinguish between itching all over (which hints at a systemic cause) and itching confined to particular locations (more likely discrete lesions).
Pruritus can be mediated by stimulation of opioid receptors, histamine receptors and endothelin-1 receptors. It may be necessary to go outside the classic opioid and histamine blocking agents with chronic pruritus and a number of drugs licensed for other indications, that act by other mechanisms, perhaps ill understood, have been shown in clinical trials to be effective in unresponsive pruritus. There is some evidence for a central nervous system itching centre mediated via opioid pathways because of problematical itching with intrathecal narcotics and baclofen withdrawal.
- Obstructive jaundice -c holestatic pruritus
- Renal failure, mainly chronic renal failure - uremic pruritus
- Lymphoma, esp. Hodgkin's lymphoma
- Other malignancies
- Can also be psychogenic in certain cases
- Opiate-induced histamine release - ?kappa opioid receptor activating 5-HT3 receptors
- Other drug related causes:
- Rifampicin - can also be used in treating cholestatic pruritus
- Intrathecal baclofen withdrawal
- Insect bites
- Skin lesions including malignancies such as melanoma
- Allergic reaction, e.g. urticaria
- Other rashes, e.g. eczema
- Specific infections, e.g genito-urinary
- Pruritus ani
- Transdermal drug delivery systems
- Endothelin-1 - well this is predictable and has been done in man to prove the point !
Robert Willan (1757-1812) classified skin diseases on morphological grounds, and it has been suggested that his name be applied to this. It may be as useful to avoid appearing to have diagnosed a cause for it, and revisit the problem from time to time.
Lots have been tried, with individual case reports of success, that fail to be replicated. Most of those specified below have randomised controlled trial evidence, some quite strong such as paroxetine in refractory pruritus.
- Treat underlying cause
- Antihistamines : The older, more sedating ones seem more effective but may lead to other problems.
- Opioid-induced pruritus
- Strontium nitrate
Inconsistent drugs tried include 5-HT3-receptor antagonists such as ondansetron.
- ↑ Ajayi AA, Kolawole BA, Udoh SJ. Endogenous opioids, mu-opiate receptors and chloroquine-induced pruritus: a double-blind comparison of naltrexone and promethazine in patients with malaria fever who have an established history of generalized chloroquine-induced itching. International journal of dermatology. 2004 Dec; 43(12):972-7.(Link to article – subscription may be required.)
- ↑ Wenzel RR, Zbinden S, Noll G, Meier B, Lüscher TF. Endothelin-1 induces vasodilation in human skin by nociceptor fibres and release of nitric oxide. British journal of clinical pharmacology. 1998 May; 45(5):441-6.
- ↑ Katugampola R, Church MK, Clough GF. The neurogenic vasodilator response to endothelin-1: a study in human skin in vivo. Experimental physiology. 2000 Nov; 85(6):839-46.
- ↑ Kjellberg F, Tramèr MR. Pharmacological control of opioid-induced pruritus: a quantitative systematic review of randomized trials. European journal of anaesthesiology. 2001 Jun; 18(6):346-57.