Anal itching

Possible causes of pruritus ani (idiopathic if no cause is identified) Colorectal Chronic diarrhoea, chronic constipation, haemorrhoids (fig 1 ), fissures, fistulas, colorectal and anal cancers (including anal intraepithelial neoplasia), rectal prolapse, anal creases, anal warts Dermatological Dermatitis, psoriasis, Bowen's disease, lichen planus, lichen sclerosus (fig 2 ) Infections-condyloma accuminata, HIV, candida, gonorrhoea, threadworm, tinea cruris Bacterial-Corynebacterium minutissimum; squamous cell carcinoma, Paget's disease, hidradenitis suppurativa, perianal Crohn's disease Systemic Diabetes mellitus, thyroid disease, vitamin disorders, uraemia, polycythemia vera, liver disease (hyperbilirubinaemia), psychological Fig 1 Close-up of a thrombosed (clotted) haemorrhoid (pile) projecting from the anus Fig 2 Lichen sclerosis around the anus What you should cover History Ask about: Erythema, scales, plaques, or excoriation marks suggesting dermatological conditions such as contact dermatitis Skin tags, warts (fig 3 ), or any pathology that might make passage of faeces difficult Nodularity and scarring, which are signs of hypertrophic skin denoting chronic disease Syphilitic chancres mimic anal fissures in appearance. Chancres are predominantly associated with itch rather than pain Tinea cruris (fungal groin infection) characterised by well defined, irregularly shaped erythematous plaques Evidence of faecal leakage Lice infestation in pubic hair Fig 3 Anal warts Palpation Perform a digital rectal examination and consider proctoscopy. Patch testing to identify allergens in generalised itching Skin scrapings for microscopy and culture to identify fungal infection Skin biopsies to exclude conditions such as anal intraepithelial neoplasia Selective flexible sigmoidoscopy to exclude inflammatory bowel disease and neoplasms If pinworm infection is suspected offer formal diagnosis.