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Probability diagnosis

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Chronic dermatitis + ‘itch-scratch’ cycle + stress

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Seborrhoeic dermatitis (esp.), eczema

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Antibiotic treatment

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Contact dermatitis: clothing and perfumed toiletries

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Irritation from excessive moisture and faecal discharge/soiling (esp. elderly)

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Serious disorders not to be missed

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Crohn disease

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Anorectal carcinoma

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Extramammary Paget disease

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Sexually transmitted infections, e.g. syphilis

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Other disorders

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Candidiasis

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Tinea cruris

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Pinworm (threadworm) (esp. children)

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Psoriasis (look for fissures in natal cleft)

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Overzealous hygiene (e.g. OCD)

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Post-diarrhoea esp. chronic or recurrent

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Local anorectal conditions (e.g. piles, fissures, fistulas, skin tags, warts)

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Masquerades checklist

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Depression

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Diabetes

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Drugs (esp. antibiotics)

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Is the patient trying to tell me something?

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Psychological factors: stress and anxiety, fear of cancer.

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Key history

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This includes past history, especially chronic dermatoses (esp. seborrhoeic dermatitis and contact dermatitis), diabetes, chronic diarrhoea (e.g. Crohn disease, coeliac disease) and psychological disorders. Enquire about lifestyle factors such as excessive sweating, sports activity and habit scratching.

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Key examination

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  • General inspection of skin and anorectal area. Skin changes can vary from minimal signs to marked pathology that can show linear ulceration, maceration or lichenification

  • A full anorectal examination is necessary

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Key investigations

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  • Blood glucose

  • Urinalysis

  • Local skin scrapings and microscopy to detect organisms

  • Stool examination (for ova and parasites)

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Diagnostic tips

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  • Pruritus ani is worse at night, during hot weather and after exercise.

  • It is seen typically in adult males with considerable inner drive, often at times of stress and in hot weather when sweating is excessive.

  • In children pinworm infestation should be suspected.

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