Pruritus is defined as itching of the skin, especially without visible eruption (The Oxford English Dictionary). When this is confined to the perianal area it is known as pruritus ani (Fig. 1) 1159. Individuals vary in their capacity to feel itching; some hardly notice an extensive dermatitis while others suffer greatly from an eruption that does not usually cause itching. Within a single individual the threshold of itching also varies with the state of concentration, tiredness, or boredom.

Generalized itching is a common complaint. In the initial investigation, parasitic diseases such as scabies and infestation with body lice must be excluded. A number of organic diseases, including anaemia, uraemia, diabetes, liver disease, and reticuloses, may present with itching. Normal results of biochemical examination of urine and serum and full blood counts will exclude most of these conditions. In the absence of organic disease or local skin disorders a diagnosis of psychogenic irritation may be made. The most common site for intractable localized itching is the anogenital region.

Eczema, psoriasis, lichen planus, seborrhoeic intertrigo, and allergic eruptions are encountered most frequently in patients with pruritus ani.

On inspection of the perineum, the anal lesions responsible for pain, discharge, and difficulty in cleaning the perineum may be seen.

Local applications, particularly local anaesthetic ointments, are a common cause of contact dermatitis. This may be exacerbated by excessive trauma caused by toilet paper (bottom polishing!), or contact with perfumes in tissues, soaps, and biological detergents.

Fungal infection may occur on its own or complicate other anal pathology. Recent treatment with broad spectrum antibiotics may encourage growth of Monilia. Ringworm should be suspected if there are active lesions between the toes, which must always be inspected. Threadworm infestation is often found in children.

Sexually transmitted disease such as herpes, anal warts, and HIV infection, must be excluded, particularly in the male with poor anal tone, a finding which suggests the possibility of homosexuality and the risk of HIV infection.

Sphincter incompetence will be seen in a small group of patients for whom a sphincter repair may be appropriate.

The patient must be undressed completely for a full examination and inspection of the skin. The perineum should be examined carefully for moisture and soiling, skin maceration and excoriation, a skin eruption, perianal lesions, and prolapse. Separation of the buttocks will demonstrate the presence of a gaping anus due to poor anal tone, and digital examination will confirm this. Digital examination together with sigmoidoscopy and proctoscopy will also identify sphincter incompetence, fistulae, haemorrhoids, and rectal lesions.

If fungal infection is suspected, skin scrapings should be taken for microbiological examination. Serological tests must be requested if sexually transmitted disease is suspected. Microscopy and culture are necessary to exclude specific infections by agents responsible for diarrhoea. Worm infestation can be diagnosed by the presence of ova on microscopic examination of a swab from the perianal skin. Rectal lesions should be biopsied and anorectal physiology studied in patients with sphincter incompetence. Table 1 350

In severe pruritus a vicious circle becomes established whereby the pruritus causes scratching which leads to secondary bacterial or fungal infections, which are treated by a multitude of topical applications, often containing local anaesthetic, which in turn produces more sensitization and more scratching, making the pruritus ani worse (Fig. 3) 1161.

The first step is to control infection and then to stop all topical applications. A cream containing low-dose hydrocortisone (1 per cent) combined with an antifungal agent (miconazole nitrate 2 per cent) should be applied to the perianal area. If severe inflammation and infection are present, a stronger steroid is used, for example a cream containing triamcinolone acetonide 0.1 per cent, gramicidin 0.025 per cent, neomycin 0.25 per cent, and nystatin 100000 units/g. These creams should be used for approximately 2 weeks, and sparingly thereafter. In the long term a patient with very dry skin may be helped by moisturizing cream or lotion (Johnson's Baby Lotion® for example); conversely, a powder will dry excessively moist skin.

Despite the topical application of medications, itch at night may continue to be a major problem. An antihistamine (promethazine hydrochloride 10–25 mg) will control this, although it may cause drowsiness. Anal lesions which require surgery should be excised after the pruritus has improved. Using this approach the majority of patients with pruritus will be cured, although most understand that a lasting cure requires a great deal of effort on their own behalf. At the end of the first consultation, the patient should be given general advice on anal hygiene, which is reinforced by a leaflet giving a list of ‘do's and don'ts’. This leaflet is a good way of ending the consultation and providing the obsessional patient with a well defined strategy.