Pruritus ani(Perianal itching)

What is pruritus ani?

Pruritus ani is a chronic perianal itching that may result in disruption in quality of life, irritability and depression. Itching may persist for weeks or even years. Two main types of pruritus ani are defined; primary (idiopathic) type in which there is no underlying cause or condition and the secondary type in which anorectal cause, dermatological or colonic disorder could be addressed. Primary(idiopathic) pruritus ani is responsible for 50–90% of all cases of pruritus ani and it is more common than secondary cases.

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Causes of secondary pruritus ani include

• Skin inflammatory diseases
  • Contact dermatitis.
  • Atopic dermatitis.
  • Seborrheic dermatitis.
  • Psoriasis.
  • Lichen planus.
  • Lichen sclerosus in females.
  • Urticaria.
  • Hidradenitis suppurativa.

• Infections
  • Bacterial
    • Staphylococcus aureus, β‐haemolytic streptococci.
    • Erythrasma (Corynebacterium minutissimum).
    • Gonorrhoea, syphillis.
  • Fungal
    • Candidiasis.
    • Dermatophytes infection.
  • Viral
    • HPV.
    • HSV.
    • HIV.
  • Paraisitic
    • Enterobius vermicularis (Pinworms).
      • Multiple family members may be affected.
    • Phthiriasis pubis (pubic lice).
• Ano-rectal diseases
  • Inflammatory bowel disease.
  • Haemorrhoids.
  • Anal fissure.
  • Perianal fstula,or abscess.
• Malignant or premalignant perianal diseases
  • Extramammary Paget disease.
  • Anal intraepithelial neoplasia, anal carcinoma.
• Neuropathic : due to compression or irritation of lumbosacral nerves from
  • Prolapsed intervertebral discs.
  • Vertebral body fractures.
  • Osteophytic processes.
• Systemic diseases
  • Diabetes, renal, thyroid and liver disease.
  • Iron defciency anaemia.
  • Leukaemia and lymphoma.

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How idiopathic pruritus ani occurs ?

The corner stone of idiopathic type is fecal contamination (fecal soiling). Feces contains irritants and allergens that may cause itching and inflammation, but what are the predisposing factors of fecal contamination. The following factors may be involved:

• Unclean perianal area
  • Anatomical abnormality
    • Funnel anus ( deeply seated anus is difficult to be completley cleaned).
    • Hirsuitism.
  • Obesity : obese patients may have poor ventilated perianal area.
• Anal incontinence may be caused by
  • Local causes
    • Haemorrhoids.
    • Perianal tags.
    • Fissures.
  • Anal sphincter dysfunction
    • Excessive coffe intake. Caffiene can lower anal resting pressure.
• Frequent loose stool
  • e.g cases of irritable bowel syndrome.
• Others
  • Foods and drinks (uncertain)
    • coffee, tea, cola, beer, chocolate, tomatoes, spices and citrus fruits.
  • Psychological factors
    • Stress and anxiety.
    • Everyday problems in tense indididuals can induce a profound colonic reflex, resulting in defecation and fecal soiling.

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History taking in pruritus ani(Perianal itching)

• The patient usually complains of itching, stinging or soreness.
• History of any bowel diseases e.g IBS.
• Ask about the cleaning routine used by the patient
  • Frequent wiping the skin with toilet papers may induce itching.
• History of anorectal operations
  • Anorectal surgery may alter the morphology and physiology of the ano-rectal region that may lead to fecal soiling and hence pruritus ani.
• Ask about the consistency of stool
  • Frequent loose stool may result in fecal soiling.
• Exclude haemorrhoids or anal fissures, ask about bleeding per rectum or pain during and after defaction.
• The use of irritant or allergic topical products on the perianal area should be excluded.
• Ask about the commonly consumed foods and drinks.
• History of any systemic diseases.

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Skin examination

• The aim of examination is to decide whether you are facing a case of idiopathic or secondary pruritus ani. Dermatological inflammatory diseases, infections, and tumors should be excluded.
• Complete skin examination should be done.
• Perianal skin examination.
• Sometimes the skin appears normal at the time of examination.
• Mild perianal erythema may be seen in some cases.
• Secondary skin changes may appear due to rubbing or scratching such as crusting, lichenifcation, lichen simplex and erosion or ulceration.
• Ulcers or masses should be investigated and biopsy may be required.
• Secondary infection or contact dermatitis may be present.
  • Contact dermatitis may be due overwashing or using of irritant skin products.

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• In pediatric patients, pinworms should be excluded by stool examination.
• Skin patch testing to exclude allergic contact dermatitis.
• Bacterial swab.
• Fungal microscopy and culture.
• Skin biopsy.
• GIT investigaations : Rectosigmoidoscopy and/or colonoscopy in resistant cases.

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Prognosis of pruritus ani is generally good and itching can be improved on proper treatment. Some cases may be challenging due to the idioapthic nature of the condition.

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Read more : How to treat pruritus ani(anal itching)?

• Griffiths, C., Barker, J., Bleiker, T. O., Chalmers, R., & Creamer, D. (Eds.). (2016). Rook’s textbook of dermatology. John Wiley & Sons.
• Pruritus Ani.