Anal intraepithelial neoplasia (AIN)

Anal intraepithelial neoplasia (AIN) is a condition that affects the skin around your anus. It is classified into three grades (I to III), with AIN III being the most severe. AIN is significant because, in some cases, AIN III can develop into anal cancer.

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What causes anal intraepithelial neoplasia?

Most cases of AIN are caused by the human papillomavirus (HPV), the same virus responsible for anal warts. AIN is also linked to changes in the vulva (vulval intraepithelial neoplasia, VIN) and the cervix (cervical intraepithelial neoplasia, CIN) in women. HPV is the common factor among these conditions.

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Other risk factors for AIN include:

• Smoking

• Weakened immune system (e.g., people taking immunosuppressive drugs, transplant patients, or those with HIV)

 

If you have AIN and a weakened immune system, you are at a higher risk of developing anal cancer.

 

What are the symptoms of anal intraepithelial neoplasia?

Many people with AIN may not notice any symptoms. When symptoms do occur, they often include:

• Persistent itching around the anus

• Small raised nodules or tags around the anus

 

AIN can affect small, localised areas of the skin or, in some cases, extend over larger areas or mutliple areas. Multifocal disease is more common in people with weakened immune systems.

 

How is anal intraepithelial neoplasia diagnosed?

When you visit the clinic, your specialist will take a full medical history and carry out a clinical examination. This usually includes:

• Rigid sigmoidoscopy – a short test to examine the rectum and lower bowel

• Proctoscopy – a detailed inspection of the anal canal

 

To confirm the diagnosis, skin biopsies are taken. The consultant may collect multiple small biopsies from around the anus to assess the extent of AIN, a procedure known as mapping. This is usually done under general anaesthesia.

If you are a woman, we may also recommend a gynaecological assessment to check for related conditions such as vulval or cervical changes.

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Treatment for anal intraepithelial neoplasia

The treatment of AIN depends on its severity:

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AIN I & AIN II

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• These lower-grade changes often do not require immediate treatment

• Regular monitoring is advised to ensure the condition does not progress

 

AIN III

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• If AIN III is localised, surgical excision (removal of the affected area) is recommended. This is typically a day-case procedure performed under a short general anaesthetic

• The wound is usually left open to heal naturally over time

 

If you require surgery, we will provide comprehensive aftercare guidance. You can also access our aftercare guide for anal surgery for detailed recovery instructions.

 

Extensive AIN III (multifocal disease)

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If AIN III affects a larger area, your specialist may recommend:

• Excision of suspicious or raised areas

• Topical treatments such as Imiquimod cream, which may help reduce abnormal skin changes

• Skin grafts in very rare cases where extensive removal of skin is necessary

 

If left untreated, AIN III can occasionally develop into anal cancer, so regular monitoring and follow-up visits are essential.