Similar changes can occur in women in the vulva (VIN) and cervix (CIN). There are different grades of AIN according to how the cells look under the microscope, from AIN1 (minor changes) to AIN3 (more severe changes).
AIN is important to identify because there is a risk that it can transform into anal cancer over many years. Overall this risk is low, but factors such as weakened immune system due to HIV infection or drugs for organ transplants may increase the risk.
Most people who have AIN have no symptoms and don't know they have it. If symptoms do occur, they may include discolouration of the skin, itching, pain, lumpy skin or rarely, bleeding. AIN is often associated with the presence of a virus known as the human papilloma virus (HPV). Smoking, usually in combination with the HPV infection, accelerates the development of AIN. The treatment and surveillance of patients will depend on their risk factors and the type of AIN they have.