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Probability diagnosis

Chronic dermatitis + ‘itch-scratch’ cycle + stress

Seborrhoeic dermatitis (esp.), eczema

Antibiotic treatment

Contact dermatitis: clothing and perfumed toiletries

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

Serious disorders not to be missed

Crohn disease

Anorectal carcinoma

Extramammary Paget disease

Sexually transmitted infections, e.g. syphilis

Other disorders


Tinea cruris

Pinworm (threadworm) (esp. children)

Psoriasis (look for fissures in natal cleft)

Overzealous hygiene (e.g. OCD)

Post-diarrhoea esp. chronic or recurrent

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

Masquerades checklist



Drugs (esp. antibiotics)

Is the patient trying to tell me something?

Psychological factors: stress and anxiety, fear of cancer.

Key history

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.

Key examination

  • 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

Key investigations

  • Blood glucose

  • Urinalysis

  • Local skin scrapings and microscopy to detect organisms

  • Stool examination (for ova and parasites)

Diagnostic tips

  • 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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