Q. Could you please discuss spinal stenosis as a cause of back pain? I had pain and numbness in my legs for months. Initially, my doctor thought I had blockages in the arteries in my legs. But it turns out I have a narrow area in my spine. Now my doctor is recommending that I have surgery for it. Does this seem reasonable? I haven't been able to find much information about spinal stenosis. What causes it? What options do I have for treatment?

A. Although many people have never heard of spinal stenosis, it's a notable cause of back pain in middle and older age. Besides back pain, it can also give you pain, numbness and tingling in the legs. Unlike the typical causes of back pain, however, this condition responds fairly well to surgery. In fact, in severe cases, it's important to have surgery to prevent further damage to your spinal cord.

Spinal stenosis literally means a narrowing of the spinal canal, a thumb-width channel that runs along the column of vertebrae that make up the backbone. Within this canal is the spinal cord, the bundle of nerves that runs from the brain to the lower spine. The backbone normally protects the spinal cord from damage, but the spinal cord can become squeezed in its already tight space by bones or other structures along the spine. When that happens, the symptoms of spinal stenosis appear.

Spinal stenosis is more than just a pinched nerve in the back. It's really a pinched spinal cord. A pinched nerve generally occurs when one of the disks between vertebrae bulges out against a nerve. With spinal stenosis, something compresses the spinal cord itself, typically along several vertebrae.

Spinal stenosis typically starts in middle age or later. As the body ages, wear and tear on the backbone can lead to bulging disks or arthritis of the spine. When these changes occur in a key area, they can narrow the spinal canal and put pressure on the spinal cord. Because of the way the backbone is built, spinal stenosis usually occurs in the lower part of the back. (Although the back problem for which Cal Ripken Jr. recently had surgery also affected the lower back, it does not seem to have been caused by spinal stenosis.)

The symptoms of spinal stenosis include pain in the back and down the legs, and burning, cramping, tingling, weakness or numbness in the legs. Unlike a pinched nerve in your back, which usually affects just one leg, spinal stenosis usually affects both legs. The pain is typically worse when standing straight, walking or leaning backward. It tends to be better when sitting or bending forward.

Walking often brings out the pain, which can make spinal stenosis seem similar to another cause of leg pain called intermittent claudication. In this condition, the pain results from not enough blood getting to the feet because of blockages in the arteries. A doctor can do some simple tests, such as checking the blood pressure in the lower legs, to see if the pain is due to poor blood flow.

To check for spinal stenosis, a doctor will examine a patient's back and legs, checking reflexes as well as looking for other causes of back pain. At times, it may be helpful to do an examination before and after walking, to see if the walking brings out symptoms. One clue to spinal stenosis is developing pain in the buttocks after bending backward for 30 seconds.

A doctor who suspects spinal stenosis may order special X-rays, such as an MRI or CT scan of the lower spine. These will show if the spinal canal is narrowed and the spinal cord is pinched. Doctors will also check for a few other less common problems that might cause narrowing of the spinal canal.

For mild cases of spinal stenosis, a doctor might recommend physical therapy, manipulation of the back and avoiding activities that cause the pain. A patient with spinal stenosis that's causing severe symptoms might be referred to a back surgeon. A surgeon might try to relieve the pressure on the spinal cord by opening up the spinal canal and creating more room for it. Because the narrowing may span several vertebrae, a patient might need to have surgery involving several backbones along the lower spine. This surgery helps most of the people who have it.

Jay Siwek, chairman of the department of family medicine at Georgetown University Medical Center, practices at the Fort Lincoln Family Medicine Center and Providence Hospital in Northeast Washington.

Consultation is a health education column and is not a substitute for medical advice from your physician. Send questions to Consultation, Health Section, The Washington Post, 1150 15th St. NW, Washington, DC 20071. Questions cannot be answered personally.