Tingling, burning, numbness and weakness. The symptoms of peripheral neuropathy are usually obvious, painful—and potentially debilitating. Yet the disorder is not always easy to diagnose.

About 20 million people in the US have peripheral neuropathy, a condition caused by damage to the peripheral nervous system. Most of these cases are linked to diabetes. But there are millions of other people who suffer from this condition and don’t know why.

In fact, for about 30% of people with peripheral neuropathy, the cause remains mysterious. In these cases, it’s diagnosed as “idiopathic” neuropathy—the same as saying “unknown cause.”

The problem: Without identifying and treating the underlying cause of peripheral neuropathy, the symptoms will only get worse. At its most extreme, neuropathy can lead to difficulty standing or walking, as well as nonstop agony from dying nerves. While symptoms can be treated without knowing the cause, addressing the root of the problem is far more effective and may eliminate the neuropathy.

THE BASICS

Our peripheral nerves are in constant communication with our central nervous system (brain and spinal cord). Communication signals are transmitted to and from the central nervous system and all the distant (peripheral) parts of the body, such as the hands and feet.

Peripheral neuropathy occurs when the peripheral nerves become damaged—as a result of diabetes…or a less commonly recognized issue (see examples below). Those impaired nerves send pain or pins-and-needles tingling sensations…or they can fail to transmit physical signals, leading to numbness or muscle weakness. There’s also the risk for injury when damaged nerves prevent you from feeling pain in dangerous situations.

THE BEST-KNOWN CULPRIT

Most people realize that neuropathy is commonly caused by diabetes (type 1 or type 2). It accounts for nearly two-thirds of all peripheral neuropathy cases. What happens: High blood sugar damages cells lining the blood vessels that transport nutrients and oxygen to body cells, which in turn harms nerves.

What you may not realize: When it comes to peripheral neuropathy, prediabetes (a precursor to diabetes) may be just as hazardous as full-blown diabetes. Nerve cell damage starts early. About 20% of patients newly diagnosed with diabetes already have neuropathy.

SURPRISING CAUSES

Besides diabetes, dozens of conditions can lead to neuropathy, including some that primary care physicians often don’t consider, such as…

• Celiac disease. This autoimmune disorder causes the body to mount a powerful defense against gluten, a protein found in wheat, rye and barley. Eat a slice of wheat bread, and the body creates antibodies that attack the small intestine. The antibodies also cause general inflammation, which is thought to cause nerve damage.

Important: Neuropathy may be an early sign of celiac disease. And contrary to common belief, it can begin at any age. Celiac disease should always be considered when peripheral neuropathy is present. A blood test can be used to check for celiac antibodies. If tingling and numbness improve after going gluten-free, it’s likely that celiac is the cause of the neuropathy.

• Bariatric surgery. Bariatric surgery for extreme weight loss is becoming more common, but it can cause a vitamin deficiency. This is partly because the surgery alters the digestive system in a way that can prevent nutrients from being properly absorbed. For example, some surgeries remove the part of the stomach responsible for creating a protein called intrinsic factor, which allows the body to absorb vitamin B-12. Severe B-12 deficiency leads to neuropathy.

Important: Neuropathy due to vitamin B-12 deficiency is also more common in people who follow a strict vegan or vegetarian diet. Long-term use of the medications metformin (for blood sugar control) or proton pump inhibitors (for acid reflux) also block B-12 absorption. A fasting blood test can determine your B-12 level. If it’s less than 200 pg/mL, a B-12 deficiency may be causing your neuropathy.

• Kidney disease. If your kidneys can’t properly filter toxins from your blood, the buildup of toxins can harm your nerves. Left untreated, even mild chronic kidney disease can result in peripheral neuropathy. Kidney disease is diagnosed with blood and urine tests.

• Hepatitis C. This virus causes white blood cells to create substances in the blood called cryoglobulins, abnormal proteins that damage nerve cells. A blood test can determine if you have hepatitis C.

• Paraneoplastic syndrome. When battling cancer, our bodies create antibodies to the cancer cells. Paraneoplastic neuropathy occurs when there is a cross-reaction between tumor cells and components of the nervous system. It can come on quickly, progress rapidly and is often extremely painful. Important: In some cases, neuropathy may be the first outward sign of cancer—and may be a vital diagnostic clue. This is especially true with lung cancer.

Since there are so many conditions that can cause neuropathy, in most cases your physician will determine the cause only after a thorough medical exam and after ruling out unlikely conditions.

WHAT YOU CAN DO

Neuropathy damage isn’t necessarily permanent. Our bodies naturally repair our nerve cells all the time. However, the only way to halt the damage and repair your nerves is to get control over the original disease process. For diabetes, maintain tight control over blood sugar levels…for celiac disease, avoid gluten…seek care for kidney disease or hepatitis C…and get appropriate medical vitamin supplementation for a B-12 deficiency. Unfortunately, treating cancer with chemotherapy may cause neuropathy, which may improve if the chemotherapy regimen is changed.

If you smoke: Neuropathy is one more reason to quit. Nicotine constricts blood vessels, which can starve nerves of the oxygen they need and increase injury to nerves that are already damaged.

Also: Alcohol is one of the most common causes of neuropathy in the US. If you drink heavily or have neuropathy due to an underlying condition, cut down on alcohol use or stop drinking altogether.