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Pruritus or itching is a cutaneous sensation leading patients to regularly and severely scratch either because of a skin lesion or in the absence of any skin lesion. Scratch lesions may occur if pruritus is severe. Pruritus can be of moderate intensity and is generally and well tolerated, however it can also be intense involving considerable discomfort for the patient.

Pathophysiology

Many external stimuli (physical or chemical) can provoke pruritus but also endogen stimuli (such as histamine, proteases, prostaglandins or neuropeptides). On the skin, pruritus is sensed by nociceptive unmyelinated fibres C (free endings) quite different from myelinated A fibres which transmit pain sensation. The influx conduction is relatively slow. Endogeneous pruritus is less characterised for its nervous conduction system.

Pain and pruritus do pass through the same neurological networks. At medullar level, opioids generally provoke a pruritus sensation whereas naloxone (opioid antagonist) has an anti-pruritic effect. Pruritus related to cholostasis is well controlled with anti-5HT3 treatment.

Pruritus classification

Primary pruritus

Primary pruritus is pruritus for which dermatological disease has been excluded. The main causes are:

biliary hepatic or pancreatic disease (in association with cholostasis)

renal insufficiency and uraemia,

various drugs (opioids, amphetamine, cocaine, aspirin, etc..),

endocrine disease (diabetes, hyperparathyroidism, thyroid disease),

haematopoietic diseases (Hodgkin's lymphoma, non Hodgkin's lymphoma, fungoid mycosis, mastocytosis, multiple myeloma, polycythaemia vera),

malignant tumours (breast, stomach, lung, carcinoid syndrom),

infectious diseases (syphilis, parasitic infection, HIV, candidiasis),

neurological disorders (distal small fibre neuropathy, tabes dorsalis, multiple sclerosis, psychosis, etc..).

In theses diseases, a liberation of mediators (such as proteases or histamine) leads to generalised and intense itching.

Secondary pruritus

Is associated with dermatological diseases

Treatment

Topical treatment

Topical treatments should be applied in case of localised pruritus or a localised region with accentuated itching. A number of preparations are active although generally for a short period of time (phenol, menthol, camphor, diphenhydramine, lidocaine, isothipendyl, local anti-inflammatory drugs).

Daily skin care is important in order to avoid scratch lesions: nails should be cut short, cool baths should be taken, soothing milky ointments should be applied, light clothes (no wool or synthetic) should be worn, including possibly humid cotton clothes which can be changed several times per day.

General medications

Among the various drugs proposed:

non-sedative antihistaminic (non anticholinergic) or sedative drug,

opioid antagonists (naloxone),

serotonin antagonists (ondansetron, granisetron),

thalidomide,

anaesthetic agents (propofol),

rifampicine is used during severe cholostasis.

Icteric pruritus (for example in pancreas cancer) is rapidly relieved by internal biliary diversion.