Spastic colon, now known as irritable bowel syndrome, affects 58 million Americans and represents one of the most common complaints encountered by doctors, according to the Washington University School of Medicine Section of Colon-Rectal Surgery. Pain is considered one of the cardinal symptoms of spastic colon. The disorder results in three different kinds of pain, each with its own slightly different set of causes.
Abdominal pain due to spastic colon is typically described as crampy and episodic or dull and aching, or sometimes both. Crampy pain is caused by contraction of the muscles that line the colon. In people with spastic colon, the muscles may contract more forcefully than normal, or they may contract when they shouldn't. Either scenario results in pain. Dull, aching pain is caused by distention of the colon due to accumulated stool and trapped gases. Both kinds of pain may seem to arise generally within the abdomen, rather than specifically from the colon. This is because pain signals from the colon enter the spinal cord at several levels at the same locations that pain signals from the skin and muscles of the abdomen also ascend. The brain, therefore, attributes colon pain to diffuse areas of the abdomen.
Patients with spastic colon often suffer from rectal pain, although they may be too embarrassed to admit it. Rectal pain due to spastic colon has two basic causes: distention and mechanical irritation. The rectum works like a reservoir for stool, but it's not designed for long-term storage. In normal people, distention triggers a bowel movement. In people with spastic colon, the bowel movement may not occur, but the urge to have a bowel movement gets worse, to the point of pain. In addition, the tissue of the rectum is thinner than that of the colon, resulting in mechanical irritation when that tissue finds itself in prolonged contact with hard, dry stools. Irritation may start out as a sensation of itching or dryness that progresses to burning or stinging pain.
Anal pain due to spastic colon results from stretching and sometimes even cracking of the muscular ring of the anal spincter and abrasion of the surrounding tissue by stool or toilet paper. For patients with diarrhea due to spastic colon, stretching and cracking may not be a problem, but chemical irritation from wet diarrheal fluids and mechanical trauma due to wiping usually are. In addition, most complications of spastic colon such as rectal prolapse, anal fissures and hemorrhoids also present at the level of the anus, where they cause their own set of pain and problems.