The itching skin pruritus

It is sometimes very difficult to help a patient with a persistently itching skin, particularly if there is no apparent cause. Pruritus is a general term for itching skin, whatever the reason.

Itching with skin manifestations

Eczema is associated with itching due to the accumulation of fluid between the epidermal cells that are thought to produce stretching of the nerve fibres. As a result of persistent scratching there is often lichenification which conceals the original underlying areas with eczema. Exposure to irritants and persistent allergic reactions can produce intense itching and should always be considered.

"Allergic reactions" due to external agents often cause intense itching. Systemic allergic reactions such as a fixed drug eruption, erythema multiforme, and vasculitis are less likely to cause pruritus.

Psoriasis, which characteristically has hyperkeratotic plaques, usually does not itch but sometimes there can be considerable itching. Occasionally this is due to secondary infection of breaks in the skin surface.

Lichen planus presents with groups of flat-topped papules which often cause an intense itch. Blistering disorders of the skin may itch.

In herpes simplex there is usually burning and itching in the early stages.

Treatment of occupational dermatitis

The exact cause of the dermatitis should be identified as far as possible. It is important to ascertain exactly what an individual's job entails; for example, a worker in a plastics factory had severe hand dermatitis but the only positive result on patch testing was to nickel. On visiting the factory it became clear that the cause was a nickel plated handle that he used several thousand times a day and not the plastic components that the machine was making. It is also important to assess the working environment because exposure to damp and irritants (for example, on an oil rig or in a coal mine) can irritate the skin.

If occupational factors are suspected, then a full assessment and investigation in a dermatology department is important as the patient's future working life may be at stake

Investigations

• Skin scrapings for mycology

• Patch testing for allergies

• Full blood count, erythrocyte sedimentation rate, liver and renal function tests

• Urine analysis

• Stools for blood and parasites

Systemic causes

• Endocrine diseases—diabetes, myxoedema, hyperthyroidism

• Metabolic diseases—hepatic failure, chronic renal failure

• Haematological—polycythaemia, iron deficiency anaemia

• Malignancy—lymphoma, reticulosis, carcinomatosis

• Psychological—anxiety, parasitophobia

• Tropical infection—filariasis, hookworm

In herpes zoster there may be a variable degree of itching, but this is overshadowed by the pain and discomfort of the fully developed lesions.

By contrast, bullous impetigo causes few symptoms, although there may be extensive blisters. Itching is usually not present.

Dermatitis herpetiformis is characterised by intense persistent and severe itching that patients often describe as being unendurable. Usual measures such as topical steroids and antihistamines have little if any effect.

By contrast, the blisters of pemphigoid do not itch although the earlier inflamed lesions can be irritating.

Parasites. Fleas and mites cause pruritic papules in groups. The patient may not realise that they may have been acquired after a walk in the country or encountering a dog or cat. Nodular prurigo may develop after insect bites and is characterised by persistent itching, lichenified papules, and nodules over the trunk and limbs. The patient attacks them vigorously and promotes a persisting "itch-scratch-itch" cycle which is very difficult to break.

Parasitophobia is characterised by the patient reporting the presence of small insects burrowing into the skin which persists despite all forms of treatment. The patient will produce small flakes of skin, fibres of clothing, and pieces of dust, usually in carefully folded pieces of paper, for examination. These should always be examined and the patient gently informed that no insect could be found but this will not be believed. Treatment is therefore very difficult and sometimes recourse has to be had to psychotropic drugs (see page 106).

Infestations with lice cause irritation and a scabies mite can cause widespread persistent pruritus, even though only a dozen or so active scabies burrows are present. It is always acquired by close human contact and the diagnosis may be missed unless an adequate history of personal contacts and a thorough clinical examination is carried out. However, a speculative diagnosis of scabies should be avoided.

Itching with no skin lesions

If no dermatological lesions are present generalised pruritus or itchy skin may indicate an underlying internal cause. In elderly patients, however, the skin may itch simply because it is dry. Hodgkin's disease may present with pruritus as a sign of the internal malignancy long before any other manifestations. A 35 year old ambulance driver attended the dermatology clinic with intense itching but a normal skin and no history of skin disease. His general health was good and both physical examination and all blood tests were normal. However, a chest x ray examination showed a mediastinal shadow that was found to be due to Hodgkin's lymphoma. Fortunately this was easily treated. Other forms of carcinoma rarely cause pruritus.

Metabolic and endocrine disease

Biliary obstruction and chronic renal disease cause intense pruritus. Thyroid disease can be associated with an itching skin. In hyperthyroidism the skin seems normal but in hypothyroidism there is dryness of the skin causing pruritus.

Blood diseases. Polycythaemia and iron deficiency are sometimes associated with itching skin.

Treatment

Treatment of the cause must be carried out when possible. Calamine lotion cools the skin with 0-5% menthol or 1% phenol in aqueous cream. Camphor-containing preparations and crotamiton (Eurax) are also helpful. Topical steroid ointments and occlusive dressings may help to prevent scratching and may help to break the itch-scratch-itch cycle. Emollients should be used for dry skin.

Topical local anaesthetics may give relief but intolerance develops and they can cause allergic reactions. Sedative antihistamines at night may be helpful. In liver failure cholestyramine powder may help to relieve the intense pruritus, as this is thought to be due to bile salts in the skin.

Antihistamines can be helpful both for their antipruritic effect and because many are sedative and enable the itching patient to sleep.

Pruritus ani is a common troublesome condition and the following points may be helpful:

• Advise gentle cleaning once daily and patients should be advised to avoid excessive washing.

• Avoid harsh toilet paper, especially if coloured, because cheap dyes irritate and cause allergies. Olive oil and cotton wool can be used instead.

• Weak topical steroids will help to reduce inflammation, with zinc cream or ointment as a protective layer on top.

• Anal leakage from an incompetent sphincter, skin tags, or haemorrhoids may require surgical treatment.

• There may be an anxiety or depression and prutitus ani itself can lead to irritability and depression.

Pruritus vulvae is a persistent irritation of the vulva which can be most distressing and is most common in postmenopausal women. It is important to eliminate any factors that may be preventing resolution. These include:

• Secondary infection with pyogenic bacteria or yeasts

• Eczema or contact dermatitis

• Lichen sclerosus atrophicus.

The adjacent vaginal mucosa should be examined to exclude an intraepithelial neoplasm or lichen planus. Treatment includes suitable antiseptic preparations such as 2% eosin, regular but not excessive washing, emollients, and topical steroids, bearing in mind the possibility of infection.

Further reading

Adams RM. Occupational skin disease, 2nd ed. Philadelphia: Saunders, 1990

Arndt KA. Manual of dermatological therapeutics, 5th ed. New York: Little, 1995

Atherton DJ. Eczema in childhood. The facts. Oxford: Oxford University Press, 1994

Cronin E. Contact dermatitis. Edinburgh: Churchill Livingstone, 1980

Fisher AA. Contact dermatitis, 3rd ed. Baltimore: Williams and Wilkins, 1986

Foussereau J, Benezra JE, Maibach H. Occupational contact dermatitis. Copenhagen: Munksgaard, 1982

Schwanitz HJ. Atopic palmoplantar eczema. Berlin: Springer-Verlag, 1988

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