Proctitis is inflammation of the lining of the rectum, called the rectal mucosa. Proctitis can be short term (acute) or long term (chronic). Proctitis has many causes. It may be a side effect of medical treatments like radiation therapy or antibiotics. Diseases like ulcerative colitis, Crohn's disease, and sexually transmitted diseases may also cause proctitis. Other causes include rectal injury, bacterial infection, allergies, and malfunction of the nerves in the rectum.
The most common symptom is a frequent or continuous sensation or urge to have a bowel movement. Other symptoms include constipation, a feeling of rectal fullness, left-sided abdominal pain, passage of mucus through the rectum, rectal bleeding, and anorectal pain.
Physicians diagnose proctitis by looking inside the rectum with a proctoscope or a sigmoidoscope. A biopsy (a tiny piece of tissue from the rectum) may be removed and tested for diseases or infections.
Treatment depends on the cause of proctitis. For example, the physician may prescribe antibiotics for proctitis caused by bacterial infection. If the inflammation is caused by Crohn's disease or ulcerative colitis, the physician may recommend the drug 5-aminosalicyclic acid (5ASA) or corticosteroids applied directly to the area or taken in pill form.
source: http://digestive.niddk.nih.gov/ddiseases/pubs/proctitis/index.htm