Anal pain

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Chapter 21 ANAL PAIN

KEY POINTS

• The differential diagnosis of anal pain includes anal fissure, abscess and proctalgia fugax. Haemorrhoids rarely cause pain unless they are complicated by thrombosis.
• Patients with thrombosed external haemorrhoids (perianal haematoma) present with severe pain associated with a tense bluish lump adjacent to the anal verge.
• Patients with perianal haematoma present with severe pain and a tense bluish lump adjacent to the anal verge.
• Thrombosed internal haemorrhoids can occur when prolapse becomes irreducible. Conservative treatment involves bed rest, elevation, ice, analgesia and aperients.
• When an anal fissure is not situated in the posterior or anterior positions, a secondary aetiological factor such as Crohn’s disease, infection or malignancy should be considered.
• Proctalgia fugax is a benign fleeting pain in the perineum that often wakes patients.
• Pruritus ani results in distressing itching and excoriation around the anus.

CAUSES OF ANAL PAIN

There are many causes of anal pain (Table 21.1). Patients usually attribute anal pain to haemorrhoids. However, haemorrhoids rarely cause pain unless they are complicated by prolapse and thrombosis. There is usually some delay in presentation because of patient embarrassment. A thorough history and careful examination can usually elicit the diagnosis without need for further investigations (Figure 21.1). Occasionally, other investigations are required and may include examination under anaesthesia, biopsy and pathological analysis, sigmoidoscopy, endoanal ultrasound and magnetic resonance imaging (MRI).

TABLE 21.1 Causes of anal pain

Frequency Causes
Common
• Anal fissure
• Anorectal abscess/fistula
• Thrombosed external haemorrhoid
• Thrombosed internal haemorrhoid
• Proctalgia fugax
• Pruritus ani
• Postoperative (anal procedures)

Infrequent
• Rectal prolapse
• Foreign body
• Faecal impaction
• Hidradenitis suppurativa
• Crohn’s disease
• Low pilonidal abscess
• Bartholin’s abscess
Rare
• Anal tumours (squamous cell carcinoma, melanoma, Bowen’s disease, Paget’s disease, basal cell carcinoma)
• Rectal cancer
• Tumours of pelvic bones or organs (prostate, cervix, vulva, vagina or urethra)
• HIV and other sexually transmitted infections
• Tuberculosis and actinomycosis
image

FIGURE 21.1 Diagnosis of anal pain.

Anal fissure

Anal fissure is caused by a tear in the mucosa of the anal canal, usually from a hard stool. It causes anal pain worse on defecation, lasting for several hours and associated with a small amount of bright red rectal bleeding. Physical examination may reveal the triad of internal anal papilloma, anal fissure and external sentinel skin tag. Sphincter muscle is present in the base of the fissure. Of all anal fissures, 90% are located in the posterior region, 5% in the anterior region and 5% in other areas. When an anal fissure is not situated in the posterior or anterior positions, a secondary aetiological factor (e.g. Crohn’s disease, infection or malignancy) should be entertained. Delay in healing of anal fissures has been attributed to impaired blood supply, demonstrated on ultrasound Doppler studies and postmortem studies.

Conservative treatment with addition of aperients, increased fibre and fluid intake and warm baths after each bowel motion is effective. The addition of topical ointments can help relieve pain. Topical glyceryl trinitrate has been shown in some studies to promote healing by its effect on nitric oxide to enhance sphincter muscle relaxation. Botulinum toxin and other drugs (e.g. calcium antagonists) have been used with varying success.

Lateral internal anal sphincterotomy is the most effective surgical treatment for anal fissures. However there is a risk for future incontinence because some sphincter muscle is divided. It is unclear how much internal anal sphincter needs to be divided: some surgeons advocate division to the height of the fissure and others advocate minimal division. Posterior internal anal sphincterotomy and anal dilatation are rarely performed now because of the risk of keyhole deformity and uncontrolled sphincter tears, respectively. Other surgical options include fissurectomy (excising the edges of the fissure to stimulate healing) and advancement flaps to cover the defect.

Anorectal abscess/fistula

Anorectal abscess results from infection in the anal glands, which are situated in the intersphincteric plane. The infection can spread downwards to present as a perianal abscess, laterally to present as an ischiorectal abscess, upwards rarely to present as a supralevator or pelvic abscess, or remain to present as an intersphincteric abscess. Symptoms include throbbing pain, sometimes associated with fever or swelling. Perianal abscesses are situated adjacent to the anal verge and are usually fluctuant. Fever and other constitutional symptoms may be absent. Ischiorectal abscesses usually present as a more indurated infection lateral to the anal verge and are frequently associated with systemic toxicity. Intersphincteric abscesses are frequently missed unless a rectal examination is performed and a tender boggy mass is palpated.

The treatment for anorectal abscesses is incision and drainage. Antibiotics are not always required. Pus drained should be sent for microbiological analysis. If skin organisms are cultured, there is minimal chance of recurrence. If enteric organisms are cultured, there is a 50% chance of developing a fistula and recurrent symptoms.

Anal fistula is a tract from the anal canal to the perianal skin. They are classified as intersphincteric, transsphincteric (most common), suprasphincteric and extrasphincteric. Patients with anal fistulas present with persistent discharge of pus and/or blood from the external opening. If the external opening closes over, recurrent abscess formation will occur. Assessment of anal fistulas includes identifying the internal and external openings, the primary track, secondary extensions, and other associated diseases.

Treatment of anal fistula involves defining the anatomy, draining associated sepsis, eradicating the fistula, preventing recurrence and preserving continence. The best treatment of low anal fistulas is fistulotomy. Fistulotomy involves laying open the fistula tract to allow healing by secondary intention. If the fistula is high, more sphincter muscle is involved and division would result in incontinence. Females are at higher risk of faecal incontinence because they have shorter anal sphincter lengths than males and may have sustained occult obstetric sphincter injuries. There are many operations available for high fistula-in-ano, each with varying cure and incontinence rates (Table 21.2). The best treatment is probably mucosal advancement flap, which has high cure and low incontinence rates.

TABLE 21.2 Treatment options for high anal fistulas

Treatment Cure rate Incontinence rate
Mucosal advancement flap 60% 5%
Draining seton 20% <1%
Fibrin glue/plug 20% <1%
Cutting seton 95% Up to 30%
Fistulotomy 95% Up to 30%
Anocutaneous flap 60% 5%
Fistulectomy 55% Up to 30%

Thrombosed external haemorrhoids

Thrombosed external haemorrhoids or perianal haematomas result from a sudden increase in venous pressure or direct trauma usually from diarrhoea. Patients present with severe pain associated with a tense bluish lump (haematoma) adjacent to the anal verge. If the patient presents in the first few days, the best treatment is evacuation of the clot under local anaesthesia. If the presentation is delayed, it is often better to leave it untreated because pain would have largely subsided by then. Patients are usually left with a residual anal tag if it is untreated.

Thrombosed internal haemorrhoids

Thrombosed internal haemorrhoids can occur when prolapse becomes irreducible and the sphincter muscles restrict venous return. This can involve one haemorrhoid or be circumferential. This condition is not uncommon during pregnancy. Treatment is either conservative or surgical excision. Conservative treatment involves bed rest, elevation, topical ice to reduce swelling, analgesia and aperients. The aim of conservative treatment is to reduce the swelling and allow return of the prolapse and natural dissolution of the clot. Subsequent treatment may only require rubber band ligation of the offending haemorrhoid. Surgical excision is sometimes required during the acute event. This requires a general anaesthesia and a formal haemorrhoidectomy. Drainage under local anaesthesia is ineffective.

Proctalgia fugax

Proctalgia fugax is a sharp, deep stabbing, fleeting pain in the perineum that often wakes patients from sleep. Duration ranges from several minutes to one hour. It is more common in young men. The aetiology is unknown but may be related to spasm of the pelvic floor or internal sphincter muscle. The history is typical and simple reassurance is often sufficient. Treatment aims to relax the pelvic floor or internal sphincter. Warm baths, topical nitrates, calcium antagonists and botulinum toxin have been used for treatment.

Pruritus ani

Pruritus ani results in distressing itching around the anus and results in excoriation of the skin secondary to scratching. The causes include systemic conditions, local anal pathology and psychological disturbances (Table 21.3). Certain drugs and foods can precipitate symptoms. Drugs such as colchicine and quinidine have been implicated. Foods that induce histamine release have also been implicated, including caffeine, milk, beer, tomato and lemon.

TABLE 20.3 Causes of pruritus ani

Systemic
• Diabetes mellitus
• Jaundice
• Leukaemia
• Aplastic anaemia
• Thyroid disease
• Renal failure

Local
• Haemorrhoids
• Anal fissure
• Anal fistula
• Loose stool (incontinence/diarrhoea)
• Anal tumours (malignant or premalignant)
• Drug reaction
• Dermatological conditions (psoriasis, dermatitis)
• Infections (sexually transmitted infections, bacterial, fungal, scabies)

Local causes should be identified and treated. If no cause is readily identifiable, the patient should be reassured and simple measures taken to alleviate the symptoms. Exacerbating foods should be avoided and a high fibre diet instigated. Simple hygiene is important with removal of any particles after bowel movements with warm water or baths (not wiping with toilet paper). Use of soap should be avoided because its slightly alkaline pH can react with the slightly acidic environment of the perianal skin. Prolonged use of topical ointments should be avoided. Loose cotton underwear may ameliorate symptoms. In severe intractable cases, subcutaneous injection of methylene blue has been used to anaesthetise the skin.

SUMMARY

Patients usually attribute anal pain to haemorrhoids. However haemorrhoids rarely cause pain unless they are complicated by prolapse and thrombosis. A detailed history and careful examination can usually elicit the diagnosis.

Anal fissure is caused by a tear in the anal canal mucosa. Treatment is with aperients, increased fibre and fluid intake and warm baths. Lateral internal anal sphincterotomy is the current surgical treatment of choice.

Anorectal abscess results from infection in the anal glands. Symptoms include throbbing pain associated with fever or swelling.

Anal fistula is a tract from the anal canal to the perianal skin. Treatment involves defining the anatomy, draining associated sepsis, eradicating the fistula and preserving continence.

Perianal haematoma results from a sudden increase in venous pressure or trauma. Patients present with severe pain and a tense bluish lump adjacent to the anal verge.

Thrombosed internal haemorrhoids can occur when prolapse becomes irreducible. Treatment is either conservative or haemorrhoidectomy. Conservative treatment involves bed rest, elevation, ice, analgesia and aperients.

Proctalgia fugax is a benign fleeting pain in the perineum that often wakes patients from sleep.

Pruritus ani results in distressing itching and excoriation around the anus. Causes include systemic conditions and anal pathology. Simple hygienic approaches can often provide relief.

FURTHER READING

Bharucha AE, Wald A, Enck P, et al. Functional anorectal disorders. Gastroenterology. 2006;130:1510-1518.

De Parades V, Etienney I, Bauer P, et al. Proctalgia fugax: demographic and clinical characteristics. What every doctor should know from a prospective study of 54 patients. Dis Colon Rectum. 2007;50:893-898.

Steele SR, Madoff RD. Systemic review: the treatment of anal fissure. Aliment Pharmacol Ther. 2006;24:247-257.

Rickard MJ. Anal abscesses and fistulas. ANZ J Surg. 2005;75:64-72.

Zuccati G, Lotti T, Mastrolorenzo A, et al. Pruritus ani. Dermatol Ther. 2005;18:355-362.

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