Understanding Small Fiber Neuropathy

If you have small fiber neuropathy, you might feel tingling, burning and sometimes pain in your toes, feet and other parts of the body.

Millions suffer from small fiber neuropathy, a medical condition that occurs when the small fibers of the peripheral nervous system are damaged. It is often caused by an underlying health condition such as diabetes.

Small fiber neuropathy can be debilitating, but the good news is that often, once the underlying health condition is identified and treated, it gets better.

We talked to UNC Health neurologist Rebecca Traub, MD, to learn more.

The Peripheral Nervous System

Neuropathy is nerve damage that occurs in the peripheral nerves, which are the nerves that extend from your spinal cord out into the rest of the body, such as into your arms, legs, hands and feet. These nerves include large diameter nerve fibers, which have a lot of myelin around them; myelin is an insulating layer of protein and fatty substances.

“These larger myelinated nerves are the ones that do things like muscle strength,” Dr. Traub says. “They also are responsible for some of your sensory functions, like feeling the position of your limb in space and feeling light touch on your hands and feet. Those are what we call large fiber functions.”

In contrast, small sensory nerve fibers are much smaller in diameter and have little to no myelin. Instead of assisting with strength and balance, these small nerve fibers transmit information about pain and temperature to your brain. Small fiber neuropathy is a disease that affects those small nerve fibers. That’s why small fiber neuropathy causes tingling, burning, pain and sometimes numbness.

“Most small fiber neuropathies are what we call length-dependent, meaning the longest nerves in the body are affected first or most severely,” Dr. Traub says.

For example, those affected will often feel symptoms in the feet and toes.

“If it becomes more severe, then it can move into the lower legs or into the hands,” Dr. Traub says. “Occasionally, someone might have tingling all over the body, and there are cases where it doesn’t start in the feet.”

Small Fiber Neuropathy: A Sign of Disease or the Result of Treatment

The most common cause of small fiber neuropathy is diabetes, and even people with prediabetes can experience it.

“There are a lot of people with diabetes who have some burning in the feet, and a lot of the times, the neuropathy is presumed to be related to the diabetes,” Dr. Traub says.

A number of other medical diseases can cause neuropathy too, Dr. Traub says. The more common ones are lupus, celiac disease and vitamin deficiencies. Chemotherapy drugs are another common cause.

“Those are usually the first-line disorders that we check for and then, depending on the clinical scenario, we may send other lab testing for rare diseases that could cause neuropathy,” Dr. Traub says.

Diagnosing Small Fiber Neuropathy

In order to diagnose small fiber neuropathy, your provider will review your medical history and do a physical exam. Then your provider may conduct an EMG nerve conduction test, an electrical testing that is used to diagnose neuropathies that affect large nerve fibers. Small fiber nerves are too small to be measured by a nerve conduction test.

“They would first order that nerve conduction test to see if there’s a neuropathy of those larger nerves. If the EMG is normal, your doctor may think you have small fiber neuropathy based on the medical history,” Dr. Traub says.

Your provider may do a skin biopsy to confirm the diagnosis.

“We do a 3-millimeter punch biopsy of the skin, usually on the leg, and then the pathologist can measure the number of nerve fibers in the skin layer,” Dr. Traub says. “This is considered the most definitive test to confirm if someone has a small fiber neuropathy, but a lot of patients are diagnosed based on just clinical features without having a skin biopsy to confirm it.”

Treating Small Fiber Neuropathy

Once your diagnosis is determined, your provider will conduct a number of blood tests to look for various conditions that can cause neuropathy.

“If we can find the underlying cause and treat it, then the neuropathy can get better—those small nerve fibers are able to regrow,” Dr. Traub says.

For example, if someone with prediabetes starts a program of intensive exercise and diet and improves his or her blood sugar, the neuropathy can improve, she says.

In about a quarter of cases, the cause remains unknown, or “idiopathic.” “If we can’t find the cause,” Dr. Traub says, “then we can treat the symptoms with medications designed to treat nerve pain, tingling and burning.”

Worried you may have small fiber neuropathy? Talk to your doctor. Don’t have a doctor? Find one near you.