Up to 60% of people with diabetes will complain of numbness, tingling or pain in their toes or hands. These are symptoms of nerve damage known as diabetic neuropathy (DN).
“Diabetic neuropathies are the most common form of non-traumatic neuropathies in industrialized nations,” said Dianna Quan, MD, professor of neurology at the University of Colorado School of Medicine in Denver. “Things that sometimes go with diabetes such as smoking, high blood pressure, increased triglycerides and cholesterol are also bad for nerves.”
There are three broad types of nerves: motor, autonomic and sensory. Sensory nerves carry information about sensations from various parts of the body. This includes pain, texture or temperature. Sensory nerves are the most commonly affected by diabetic neuropathy.
The nerves of the autonomic nervous system control the “housekeeping” functions of the body such as activities of the stomach, heart, intestine and bladder.
Motor nerves tell the muscles what to do when you move.
Peripheral nerves send sensory information from the body back to the brain and spinal cord. They also can carry signals from the brain and spine to the muscles, telling them to move. Like static on your phone, neuropathies distort and interrupt these messages, resulting in numbness, tingling, weakness or pain.
“Diabetic neuropathies are injuries to the peripheral [outside of the brain or spinal cord] nerves that are secondary to the condition of diabetes,” said Eva Feldman, MD, PhD, Russell N. DeJong, professor of neurology at the University of Michigan Medical School in Ann Arbor. “The classic type starts in the nerves in the tips of your toes and then slowly moves up the body.”
This makes sense from a physical standpoint because the nerves in your toes or fingers are the farthest from their beginnings in the spinal cord. Think of them as long extension cords that might be cut or stretched.
Control is key
Neuropathies in diabetes are most often linked to lack of good control of blood sugars. The longer you have diabetes and the consistently higher your hemoglobin A1c (HbA1c) is, the more likely you will get diabetic neuropathy and the worse it will be.
While good control is important in both types of diabetes, the effect it will have on neuropathies may change if you have type 2 diabetes. In type 1, the person is usually insulin deficient when the pancreas stops making insulin. In type 2, you are insulin resistant, so your body responds by pumping out more and more insulin, but your muscles and fat cells still can’t take in enough glucose and fats.
“Clearly in type 1 patients, the DN is more closely correlated to glucose control,” said Dr. Feldman. “There are well-controlled studies showing that if you control glucose in type 1, you are less likely to have neuropathies and might even improve any preexisting damage. In type 2, even with good control, the nerve damage can continue over time.”
In type 2, there may be a problem getting the correct fuel into the nerve cells. Think of nerve cells as little power plants. You need to get something in to generate the power while also removing waste products. If you try to use diesel fuel when the plant is set up for regular gasoline, your plant won’t work as efficiently, and sludge will start to build up that eventually shuts the plant down.
Data show that controlling glucose in type 1 diabetes can reduce the incidence of diabetic neuropathy by 60% and can often slow progression. On the other hand, among those with type 2, at least 50% will show indications of diabetic neuropathies even with good control.
“With type 2 diabetes, the pathology of nerve damage is probably more multifactorial,” said Feldman. “In addition to glucose, lipids, obesity and high blood pressure run parallel with this kind of diabetes. You need to treat dyslipidemia, control weight and work with the hypertension to see a beneficial impact in type 2.”
While most experts and guidelines set HbA1c goals of 6.5% to 7.0%, that is not always the case. Indeed, some forms of diabetic neuropathy may actually make that goal dangerous to certain people.
One of the body’s natural defenses against hypoglycemia, or low blood sugar, is the release of adrenaline from the adrenal gland. If diabetic neuropathy has affected the nerve that serves this gland, then the hormone isn’t released.
“This hypoglycemic unawareness, or inability to sense low blood sugars, may mean you have to tolerate higher glucose levels to avoid frequent incidents of low blood sugar,” said Lyle Mitzner, MD, a staff physician at the Joslin Diabetes Center in Boston. “The body is wired for a specific response in the case of low blood sugars. If nerve damage means that it doesn’t work, the glucose will continue to drop, and we want to avoid that.”
An ounce of prevention
The best way to avoid diabetic neuropathies is to never get diabetes.
“From the standpoint of prevention, diabetes doesn’t happen overnight,” said Quan. “There is a period of prediabetes or impaired glucose metabolism, that is a transition between healthy blood sugar levels and frank diabetes. In that twilight zone, there is an opportunity to avoid type 2 diabetes in the first place.”
Early symptoms of diabetic neuropathy include:
• burning sensation in the toes or fingers
• pricking pain
• electric-shock feelings
• hypersensitivity to touch
• muscle weakness
• loss of reflexes
• loss of balance and coordination
As the neuropathy gets worse, you may lose feeling in your extremities. This can be the most dangerous part of the process.
“When you have nerve damage to the point you can’t feel your feet, you are at a much higher risk for developing ulcerations,” says Dr. Mitzner. “If you don’t feel a cut or scratch on your foot, you don’t know to treat it. This can lead to ulcerations, infections and possibly even amputation of the foot or toes.”
This is why your diabetes healthcare team stresses checking your feet often. The injuries can be hard to see, but further problems can be prevented when they are caught early.
Diagnosis of diabetes-related nerve damage often occurs in the diabetologist’s office. An important part of the assessment is a good history and physical examination. After all, just because you have diabetes doesn’t mean you can’t have another neurological condition.
Your healthcare provider will often use a tuning fork to test for sensitivity to vibrations and a safety pin to look for deficits in pain perception. He or she may have you push against his or her hands or grip his or her fingers to assess your strength and whether it is the same on both your right and left sides. In some cases, nerve conduction studies might be used to see if the nerve messages are getting through.
“I look at what my patient is telling me about their symptoms and see if they are consistent with what we see in diabetic neuropathies,” said Mitzner. “Not everyone will need to see a neurologist unless I see something indicating some other possible medical concern.”
Treating diabetic neuropathy pain
There are no treatments or magic pills that will reverse any damage already done to the nerves. If the symptoms are mainly things like tingling or electric shock, there is little that can be done. When there is pain, medications can help.
Currently, only two medications have been approved by the U.S. Food and Drug Administration (FDA) for use in the treatment of neuropathic pain in diabetes. These include the anti-seizure medication pregabalin (Lyrica) and the antidepressant duloxetine (Cymbalta). There is also a topical patch sold under the brand name Qutenza, which contains 8% capsaicin (a chemical compound derived from chili peppers), long used in topical ointments for pain relief.
Although they have not gone through the process of getting official FDA approval for such use, many other kinds of medications have been shown in comprehensive studies to help with pain relief. This so-called “off-label” use is accepted by many physicians and should not alarm you if prescribed. Most of these have cheaper generic versions available.
These groups include: other anti-seizure medications such as gabapentin and carbamazepine; and tricyclic antidepressants such as amitriptyline, desipramine, and imipramine.
If these do not relieve the pain, more powerful medications may be used. Opioid narcotics are available if the pain is refractory after other medications have been used.
“We can treat pain if the symptoms impact your ability to function or limit your quality of life,” said Mitzner. “Medications have side effects that can be more bothersome than the symptoms themselves. Other times, people are already on a lot of medications and don’t want to have another. Pain treatment is very individualized.”
The key message from all three experts is don’t wait until you have diabetic neuropathy. The earlier you think about it, the better off you will be.
“From my standpoint, the minute you are diagnosed with diabetes, you should be talking with your doctors about what you need to do to prevent or lessen problems for yourself in the long run,” said Quan. “And this conversation should be about more than just nerve damage.”