Pruritus ani

What is pruritus ani?

This is the sensation of persistent perianal itching, resulting in a desire to scratch the anus. It is a symptom and NOT a diagnosis.

How common is pruritus ani? (Epidemiology)¹

Pruritus ani can be an important symptom secondary to specific disease processes. Inflammatory diseases of the skin, infections, infestations, premalignant and malignant neoplasms, and anorectal and systemic diseases may cause perianal itching. More often, there is no disease-specific aetiology and this is called idiopathic pruritus ani, which is responsible for 50-90% of cases, and affects 1-5% of the general population.²

Pruritus ani is four times more common in men than in women. It can occur at any time of life but is more common between 40-60 years of age.

Causes of pruritus ani^{1 3 4}

Nearly 100 causes have been reported for pruritus ani.

Idiopathic or primary pruritus ani

This is thought to be either functional or psychological in nature:

• Functional: due to very slight faecal matter around the anus causing irritation.

• Psychological: complex aetiology.

Secondary pruritus ani

Causes of secondary pruritus ani are numerous and include:

Skin disorders
Thought to account for 50% of secondary pruritus ani.

• Psoriasis.

• Contact dermatitis.

• Atopic dermatitis.

• Skin tags.

• Lichen sclerosus.

• Lichen planus.

• Seborrheic dermatitis.

• Hidradenitis suppurativa.

• Bowen's disease.

• Extramammary Paget's disease.

Infections

• Bacterial.

• Fungal - candida, dermatophytes.

• Parasitic - threadworms or scabies. Threadworms are the most common cause in children.

• Viral - condyloma secondary to human papillomavirus, herpes simplex.

• Sexually transmitted infections - gonorrhoea, syphilis. Consider if history of anal intercourse.

Rectal and anal pathology

• Anal cancer or colorectal cancer.

• Haemorrhoids.

• Anal fissure.

• Anal fistula.

• Faecal incontinence or faecal soiling.

• Chronic diarrhoea or constipation.

Systemic disease

• Diabetes mellitus.

• Aplastic anaemia.

• Iron-deficiency anaemia.

• Leukaemia.

• Lymphoma.

• Thyroid disorders.

• Liver disease.

Medication

• Corticosteroids.

• Colchicine.

• Peppermint oil.

• Immunosuppressants.

• Antibiotics such as metronidazole or tetracycline.

• Topical preparations.

Dietary irritants

• Caffeine.

• Beer.

• Chilli peppers.

• Citrus.

• Milk.

• Tomatoes.

Assessment¹

History

• Duration and pattern of itch. Itch due to threadworms occurs mainly at night. If all family members are affected consider scabies.

• Triggers and irritants. Establish whether it is affected by certain foods, clothes or topical preparations. Ask about the use of powders, creams and soaps.

• Hygiene. Establish whether there is any difficulty in keeping the area clean or dry.

• Associated symptoms. May give clues as to the cause - eg:

  • Pain - fissure.

  • Discharge - infection.

  • Bleeding - more likely to have anal pathology such as haemorrhoids, tumour, fissure.

  • Change in bowel habit - consider malignancy.

• Past medical, allergy and medication history - to include causes in section above.

• Severity and impact on life.

Examination

• Look for dermatological conditions elsewhere.

• If symptoms suggest, perform a general examination to exclude other systemic disease.

• External examination of the area around the anus may reveal a cause such as a skin condition, threadworms, fissure.

• The appearance will depend upon the severity and duration of the pruritus.
  There may be:

  • Erythema or inflammation.

  • Excoriation and cracking.

  • A shiny appearance to the anal ring in chronic cases.

• Perform a digital rectal examination (DRE) if there is any suspicion of malignancy. Also consider DRE if there are internal haemorrhoids or in those with constipation.

• Do not perform a DRE in children.

Pruritus ani treatment and management^{1 5}

Treat secondary causes.

It is important to identify and eliminate any underlying causes, which may include unintentional consequences of the patient's attempts to alleviate symptoms. Treatment otherwise depends on any underlying cause but, if no reversible cause is found, simple measures with diet modification and perianal hygiene should be tried before using any topical medications or procedures.⁶

• Sending a skin swab for microscopy, culture, and sensitivities is reasonable.

• Refer for lower gastrointestinal investigation, or skin biopsy and patch testing if an underlying condition is suspected.

• If symptoms do not settle with self-care and symptomatic treatment after 3-6 weeks, consider the need for investigations - eg, full blood count, ferritin levels, HbA1c, thyroid function tests.

• If no cause is identified, refer the person to a colorectal surgeon to exclude an anorectal pathology.

• If no anorectal cause is found, a specialist may consider alternative treatment options for refractory pruritus ani (such as intradermal injection of methylthioninium chloride (methylene blue), dupilumab, or serlopitant).

Self-care measures

• Maintain good perianal hygiene:

  • Gently wash the perianal area with plain water after every bowel movement and at bedtime, ideally using a shower jet or by sitting in the bath. A bidet or sitz bath is useful if available.

  • Gently dry the perianal area by patting with a soft towel or cotton swabs (avoid rubbing). A hair dryer on the cool setting can also be used.

  • Avoid excessive rubbing or wiping with alcohol-based disinfectants or wet wipes.

  • Wear loose cotton underwear, avoid tight clothing, and use stockings (instead of tights), to reduce sweating or excess moisture.

  • Avoid talcum powder, soaps, perfumed products, or deodorant around the perianal area.

  • Keep the perianal area cool at night (use a light duvet or bed sheet).

  • Avoid foods and drinks known to aggravate pruritus ani, such as coffee, chocolate, citrus fruits, cola drinks, and dairy products.

  • Avoid scratching: keep nails short; wearing cotton gloves at night can help to reduce skin trauma.

  • Consider a cotton wool 'plug' to prevent soft faeces leaking from the anus during exercise.

• Ensure stools are formed and regular and avoid constipation (to reduce perianal leakage):

  • Avoid straining.

  • Beware mechanical irritation by some toilet paper.

  • Maintain adequate dietary fibre and fluid intake.

Symptomatic treatment options

• If the perianal skin is excoriated, consider prescribing a soothing cream or ointment containing zinc oxide.

• If the perianal skin is inflamed, consider a mildly potent topical corticosteroid for no longer than seven days.

• If there is disturbed sleep due to nocturnal itching, consider a sedating antihistamine.

• However, there is no evidence for the efficacy of emollients, topical corticosteroids, or oral antihistamines.

It is reasonable to relax self-care measures gradually after two months, if symptoms have settled. If symptoms recur, the regimen can be restarted.

Complications of pruritus ani¹

Persistent scratching may lead to dermatitis, excoriation, lichenification, ulceration or infection.

Depression may follow severe, persistent symptoms. Insomnia may be a problem and may reduce quality of life.

Prognosis¹

Unless a cause is found it may become a chronic complaint. However, for most people the symptoms of pruritus ani will resolve with self-care measures and symptomatic treatment, but sometimes with periodic relapse.