Pruritus ani (perianal itch)

 

Introduction

 

Pruritus ani (PA) is a chronic unpleasant itching and/or burning sensation in the perianal region. Pruritus ani can be primary (idiopathic) or secondary. The symptom of pruritus ani has many causes.  Pruritus ani can be associated with most forms of ano‐rectal disease or perianal skin disease.

Pruritus ani is considered idiopathic when no dermatological or ano‐rectal cause can be found. Idiopathic pruritus ani is responsible for 50–90% of all cases of pruritus ani. The pathogenesis of idiopathic pruritus ani is thought to be primarily the consequence of fecal contamination or possibly the intake of certain food and drinks.

 

Secondary causes of pruritus ani

 

Inflammatory skin disease

·        Endogenous eczema including seborrheic and atopic

·        Allergic or irritant contact dermatitis

·        Psoriasis

·        Lichen planus

·        Urticaria

·        Lichen sclerosus (females only)

·        Hidradenitis suppurativa

Infections

·        Candidiasis and dermatophytes

·        Erythrasma (Corynebacterium minutissimum)

·        Staphylococcus aureus, β‐haemolytic streptococci

·        Gonorrhoea, syphillis

·        Human papillomavirus, herpes simplex virus

·        Human immunodeficiency virus

Infestations

·        Threadworms (Enterobius vermicularis)

·        Pubic lice (Phthiriasis pubis)

Perianal premalignant or malignant disease

·        Anal intraepithelial neoplasia, anal carcinoma

·        Extramammary Paget disease

Ano‐rectal disease

·        Haemorrhoids, anal fissure

·        Perianal fistula, perianal abscess

·        Inflammatory bowel disease

Systemic disease

·        Metabolic including diabetes, renal, thyroid and liver disease

·        Iron deficiency anemia

·        Malignancy including leukemia and lymphoma

 

Epidemiology

 

Incidence and prevalence

 

It affects 1–5% of the general population.

 

Age

 

It most commonly presents in the fourth to sixth decade.

 

Sex

 

It is four times commoner in men than women.

 

Predisposing factors

 

The common factor causing idiopathic pruritus ani is fecal contamination. Feces contain potential irritants and allergens that are capable of inducing itch and inflammation. Patients with idiopathic pruritus ani have a high incidence of loose stool.  Any factor that increases fecal contamination exposes perianal skin to irritants. A sedentary lifestyle has been implicated.

Causes of fecal contamination include the following (more than one factor may be operative):

 

1.   Difficulty cleaning the perianal area:

o   Obesity leads to poor ventilation and maceration.

o   Anatomical factors including deeply placed ‘funnel anus’ and hirsuitism can cause mechanical problems in the maintenance of hygiene.

 

2.   Anal leakage:

o   Local causes that alter anal morphology or function such as hemorrhoids, perianal tags or fissures can lead to anal incontinence.

o   Primary anal sphincter dysfunction may result in fecal soiling. Caffeine can lower anal resting pressure.

 

3.   Loose frequent stools:

 

These will cause fecal soiling and an increase in perianal trauma from frequent wiping of the skin. Underlying conditions include irritable bowel syndrome.

 

Other contributing factors include the following:

 

1.   Food and drink. The role of food and drinks is uncertain but those implicated include coffee, tea, cola, beer, chocolate, tomatoes, spices and citrus fruits. The mechanisms proposed include effects on anal sphincter tone, production of loose stools and undigested food components irritating or sensitizing the perianal skin.

 

2.   Psychological factors. Idiopathic pruritus ani has been attributed to stress and anxiety. Patients are often tense individuals, in whom everyday problems induce a profound colonic reflex, resulting in defecation and soiling.

 

 

 

Clinical features

 

History

 

The complaint is of itching, stinging or soreness that may be chronic and recurrent. Symptoms may be triggered by a bowel movement or wiping with toilet paper, but may occur at night.

 

Presentation

 

Physical signs result from the effects of rubbing, scratching, secondary infection or contact dermatitis. There may be no visible abnormality at the time of examination.

 

Differential diagnosis

 

Fungal infection often causes intense pruritus, and diabetes must be excluded in all severe or persistent candidal infection.

 

Complications and co‐morbidities

 

Lichenification, excoriation and secondary infection can occur. A contact dermatitis can result from over washing and treatment. Patients with pruritus ani are at high risk of sensitization from topical medicaments, toiletries and wet tissue wipes. Common allergens include neomycin, fragrance mix, Balsum of Peru and methylisothiazolinone.

 

 

Disease course and prognosis

 

Generic measures usually improve symptoms in 90% of patients. Many patients who undergo surgery for hemorrhoids continue to have symptoms.

 

 

Investigations

 

Diagnostic approach in pruritus ani:

 

 

In the young, threadworms should be sought with the Cello tape test or by stool examination. Skin patch testing should be considered at an early stage.

 

Management

 

Specific secondary causes should be addressed. Management includes attention to the patient's washing habits. It is important to maintain cleanliness and to ensure that the perianal area is dried after washing. Soap substitutes should be used. An emollient should be applied after each wash. A barrier preparation can be pre applied to the perianal skin before the bowels are opened. Washing in a bidet after defecation is preferable to wiping with toilet paper. Rubbing with toilet paper should be discouraged and dabbing recommended. Premoistened toilet paper or wet wipes should be avoided. Underwear should be loose and preferably made of cotton. Topical anesthetic preparations should be avoided as sensitization commonly occurs. Fingernails should be kept short.

A reduction of coffee consumption or elimination of food or drinks implicated may help. A high‐fiber diet should be encouraged if there is any history of constipation or hemorrhoids.

Referral to a colorectal specialist is indicated if anorectal disease is suspected.

 

First line

 

The aim of treatment is to break the compulsive itch–scratch cycle. Local applications should be soothing and as mild as possible. Use of a twice daily liquid cleanser can be as effective as twice daily potent topical steroid application. Mild steroid ointments (1% hydrocortisone) can be helpful and these can be combined with antibacterial or antifungal. Caution should be exercised with topical steroids because perianal skin is occluded and atrophy may occur.

 

Second line

 

Other treatments that have been advocated include zinc paste with 1–2% phenol, 0.006% capsaicin ointment, 0.1% tacrolimus ointment, oral antihistamines, intralesional corticosteroids and corticosteroid suppositories.

 

Third line

 

Successful treatment of refractory pruritus ani with intradermal injection of 1–2% methylene blue alone or in combination with 0.5% lidocaine has been reported. Cryotherapy has also been used.

Treatment of mild-moderate idiopathic pruritus ani

Treatment of severe idiopathic pruritus ani