Q I have peripheral neuropathy, but people often confuse it with fibromyalgia. What is the simplest way to explain the difference?
DR. RICHARD A. LEWIS RESPONDS:
A Peripheral neuropathy is a collection of disorders in which peripheral nerve fibers, which carry signals to and from the central nervous system (the brain and spinal cord), become damaged. Diabetes is the most common cause. Typically, nerve fibers in the hands and/or feet are affected. Symptoms include pins and needles, numbness, tingling, and weakness.
People with fibromyalgia may experience the same symptoms. However, these symptoms tend to come and go in fibromyalgia. In peripheral neuropathy, they are usually constant.
Fibromyalgia can cause other symptoms that people with peripheral neuropathy do not experience, including pain in soft tissue areas such as muscles and joints.
When a piece of the nerve (a biopsy) is taken from someone with peripheral neuropathy and tested, abnormalities in the nerve fibers can be seen. But in someone who has fibromyalgia—even if the person has numbness and tingling—no abnormalities are typically found.
Fibromyalgia is believed to result primarily from pain-processing problems in the central nervous system. As far as we know, the peripheral nerves are not damaged in any way. People with fibromyalgia have many tender points on the body, often in the shoulders, neck, and low back. But when a piece of the nerve from these areas is tested, no abnormalities are typically found. People with fibromyalgia who have pain in their shoulders and backs often describe burning, tingling, and shooting pains in their arms and legs, which may sound like peripheral neuropathy. However, the results of nerve conduction tests—in which a series of electrical impulses are given to the nerve—are usually normal.
When someone comes to me with tingling, numbness, and burning, I need to determine whether these are symptoms of peripheral neuropathy or something else. If I don't find anything abnormal from a biopsy or a nerve conduction test and the person also has tender points, then fibromyalgia may be the cause.
The treatments for fibromyalgia that have been approved by the U.S. Food and Drug Administration—including pregabalin (Lyrica), duloxetine (Cymbalta), and milnacipran (Savella)—can also be effective in treating the pain of peripheral neuropathy. The reason is that these medicines affect pain processing in the central nervous system, and while peripheral neuropathy is caused by damage to nerves outside of the brain and spinal cord, that pain still must be processed by the central nervous system.