DEAR MAYO CLINIC: Eighteen months ago, I had surgery on my back to relieve the nerve pain that radiates down my leg. It didn't help as much as I'd hoped, and my doctor says additional surgery isn't likely to help. I have tried pain meds, steroid injections, chiropractic, and physical therapy, but I'm still in a lot of pain. What exactly are implanted pain relief devices, and would I be a candidate for one? If so, how effective are they?

ANSWER: The pain you're describing is called radiculopathy, and it is a type of nerve pain. There are several devices for pain relief from varied types of chronic nerve pain. Some rely on stimulating nerves with a mild electrical current. Other implanted devices deliver pain-relieving medication directly into the spinal canal. These devices are typically implanted by physicians specializing in pain management. Both types are usually considered only after more conservative options have failed, and they seldom provide complete pain relief. However, when they are effective, they can change debilitating pain into tolerable, manageable pain that allows you to function and regain your life.

Nerve stimulation devices work by blocking pain signals as they travel from the nerves to the spinal cord. In doing so, they send electrical impulses from the spinal cord out along affected nerves. These electrical impulses may produce a pleasant "tingling" sensation that can be directed to the area where you feel pain. The two main forms include:

1. Spinal cord stimulators. With these, a wire electrode is implanted in the epidural space within the spinal canal. It provides electrical stimulation on an area of the spinal column called the dorsal columns, which is where sensory nerves from the spinal cord are located.

Spinal cord stimulators are FDA approved for conditions that involve pain generated from damaged or dysfunctional nerves of the trunk, legs or arms. This includes problems such as radiculopathy, pain that persists after spine surgery, peripheral neuropathy, post herpetic neuralgia, and a condition called complex regional pain syndrome, which usually results in leg or arm pain.

2. Peripheral nerve stimulators. Placed along nerves that branch off from the spinal cord, these may be used for pain arising from numerous peripheral nerve problems, including remaining leg pain after back surgery, post-herpetic neuralgia and some types of headaches.

Peripheral nerve stimulators are more targeted to a specific nerve or group of nerves than are spinal cord stimulators. Occasionally, spinal cord and peripheral nerve stimulators are used in combination to achieve better pain relief.

Determining if one or both nerve stimulation devices are right for you depends on many factors, including the cause of your pain, its location, your overall health and your ability to care for an implanted device. If your doctor thinks you may be a candidate, you'll likely undergo a stimulation test with a temporarily placed electrode to find out how well you respond to the therapy. If the device had a beneficial effect, the wire electrode and the electrical generator (or battery pack) can be fully implanted under the skin during a separate surgical procedure.

Medication pumps

Technically called intrathecal drug delivery systems, these deliver pain medication directly into the fluid that surrounds the spinal cord. They're most often used to relieve pain from cancer or to relieve chronic back pain that's unresponsive to more conservative therapies. They also may be used as a "last resort" option for certain types of severe chronic pain. They may be considered if a nerve stimulator fails to provide relief, or rarely, in conjunction with a nerve stimulator.

Medication pumps consist of a small flexible catheter that's placed in the spinal fluid. The catheter is connected to a drug infusion pump that's implanted into your lower abdominal wall. The pump is programmed to dispense the drug it contains -- often opioid pain medications (such as morphine) or other medications to treat nerve pain -- at a set rate and can be refilled with an injection through your skin and into a sealed port on the device.

A key limitation of medication pumps is the eventual development of tolerance to the drugs. Dosages of pain medication can be increased as tolerance rises, but there are limits. That's why this therapy is generally used for people with limited life expectancy or those in extreme circumstances. One main advantage of this type of device is that the medication is delivered directly to the site of action (spinal cord), and the effective dose can be reduced by 100 fold from the equivalent dose by mouth. This greatly reduces the risk of side effects from the medications.

Surgery to implant any pain device carries some risk of complications, such as infection, bleeding, or even the potential for spinal cord or nerve damage. Fortunately, the risks are quite low.

Nerve stimulators and medication pumps can work exceedingly well in the right situations. When effective, a reasonable goal with these devices is to reduce pain by at least 50 percent. The main objective is to reduce pain to a manageable level, allowing improved function and quality of life. -- Halena M. Gazelka, M.D., Pain Medicine-Anesthesiology, Mayo Clinic, Rochester, Minn.
