TABLE 785 Pruritus

In Iable78:5 "anorectal disease" includes the various categories that have been discussed in this chapter. The pruritus that accompanies such conditions as fissures, fistulas, hemorrhoids, and prolapses occurs as a result of the perianal skin's being exposed to and macerated by constant mucous and purulent discharge. It is probably the increased perianal moisture caused by these conditions that results in itching. The itching triggers a vicious cycle of scratching, excoriation, and more itching.

Numerous dietary factors have been implicated and are associated with secondary pruritus ani, although proof of cause is lacking for most of them. Those dietary factors most commonly listed include excessive consumption of caffeine-containing liquids, such as coffee, tea, or colas, and beer, although one recent study failed to demonstrate any correlation between pruritus ani and alcohol consumption. Milk, chocolate, tomatoes, and citrus fruits are other food products that allegedly contribute to pruritus ani. Likewise, certain drugs, such as colchicine and mineral oil, have been associated with pruritus ani. Ingestion of these products can result in increased liquidity and seepage of fecal material, which in itself is a probable cause of pruritus ani.

Infectious agents that have to be considered as causes of pruritus ani include bacteria, viruses, fungi, spirochetes, and parasites. More common bacterial infections, such as staphylococci and streptococci, in addition to all sexually transmitted organisms, will cause pruritus, if not actual pain. Pinworms ( enterobius/vermicularis) are the most common cause of anal pruritus in children. Candida/albicans is commonly found on the perianal skin but is not usually associated with pruritus; the Trichophyton species, on the other hand, are always associated with pruritus.

Local irritants, if not the initial cause, commonly contribute to the incidence of pruritus. Fecal contamination, resulting from poor anal hygiene, is by far the most common irritant to the perianal skin. Lysozyme from intestinal mucous secretions, acting together with bacterial exotoxins to raise the stool and skin pH, will cause pruritus. Ironically, patients who compulsively clean their anus, particularly if they use perfumed toilet tissue, soaps, or detergents or hygiene sprays, cause pruritic reactions. Also, wearing of synthetic, tight-fitting underwear retains moisture that normally occurs in the perianal area, another leading cause of pruritus.

Dermatologic conditions contributing to this symptom complex include atopic dermatitis, lichen planus, psoriasis, and seborrheic dermatitis. Any of the anal margin neoplasms, particularly Bowen's disease and extramammary Paget's disease, may initially manifest itself as pruritus.

Finally, certain systemic conditions, such as diabetes mellitus, lymphoma, and certain vitamin deficiencies (vitamins A and D and niacin), because of their secondary effect on the perianal skin, will cause pruritus.

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