Conway McLean, DPM, Journal columnist

Nerves are an amazing component of human anatomy. Their ability to send a signal nearly instantaneously is what allows you to move and think. Modern science has developed a moderately detailed picture of how they work (when in a normal condition, i.e. ‘healthy’). But, as a generalization, the problems experienced by these ubiquitous structures are often difficult to diagnose. Many suffer from some nerve disease and have no symptoms, at least early on (when treatment is more effective).

The list of neurologic diseases is extensive, and includes those that are inherited, those metabolic in origin (think diabetes), traumatic disorders, degenerative nerve diseases (like Alzheimer’s and Parkinson’s), infections (e.g. meningitis or polio), and many others. One of the most common neurologic problems is peripheral neuropathy, in which there are structural changes to the nerves outside the brain and spinal cord. With these diseases, symptoms usually start farthest from your core which would be the toes. As you might imagine, there are numerous types and many causes for peripheral neuropathy.

In our society, for myriad reasons, diabetes is epidemic. And we know very well this metabolic disease causes peripheral neuropathy in the majority of those afflicted with diabetes. Yet, people diagnosed with diabetes are rarely educated about this loss of “protective sensation,” the ability to feel minor (sometimes major) skin injury.

Although their feet may “feel” normal, those with diabetic neuropathy experience the loss of function of certain types of nerves in the feet. They often won’t notice some slight insult to the skin, perhaps a coin dropped inside a shoe, or an ingrown toenail that gets infected. For these reasons, peripheral neuropathy is considered “the first step on the stairway to amputation.” When added to their reduced immune system, you have a dangerous combination.

Make no mistake about it, peripheral neuropathy is a pervasive, potentially-debilitating condition. The pain and odd sensations that may be associated with peripheral neuropathy are considerable, with some poor souls experiencing an intense burning day and night. Neuropathy is widespread, believed to affect approximately 20 million people in the US. Surprisingly, of those afflicted with peripheral neuropathy, just over a quarter have been diagnosed. Without obvious symptoms or preventative testing, how is one to know?

Unfortunately, the extent of the testing provided to most diabetics is woefully inadequate. If there is any investigation into a diabetic’s nerve health, it consists of deep tendon reflexes (the cliched tapping of the knee tendon), maybe even use of a monofilament. This is a thin plastic rod of specific thickness and length, pressed against the skin until it bends. It therefore applies a predictable amount of pressure to the skin.

Inexpensive, compact, and quite portable, the monofilament device has its attributes. But the research reveals it to be insensitive and inaccurate, a dangerous situation when the results of this test are incorrect or imprecise. Many other techniques are available, although utilized infrequently. In the two point discrimination test, the patient is touched with a single pointed object or two (which they can’t see). As the two points are moved closer together, it becomes more difficult to feel this stimuli as distinct points, especially in the face of peripheral neuropathy.

The receptors detecting vibrations are affected by many peripheral neuropathies. To evaluate the health of these nerve receptors, an electronic device producing an exact vibration can be used. Placed against a body part, typically the great toe, the individual tells the examiner when they stop feeling it as the vibration is gradually reduced, giving detailed information about the severity of their neuropathy.

But these are all subjective tests, which means the patient is part of the test. We’re not testing just the nerve receptor, but many other structures. For more specific measurements, objective tests provide concrete, precise information about the condition of the actual nerve structures. Many healthcare providers order an EMG, an electromyogram, when they suspect small fiber neuropathy (SFN). Unfortunately, this is not a good test for this disease because it examines only large nerve fibers. These become diseased only very late in the process. If this test is positive, all hope for these nerves is lost; it is too late and too much degeneration has occurred.

More than 25 years ago, researchers at Johns Hopkins University developed the epidermal nerve fiber density test, which allows us to literally examine these tiny skin nerves. This was the first test that allowed us to objectively measure peripheral neuropathy. It is still considered the gold standard, our most precise measurement, the downside being it is invasive. Although it only requires a small, round piece of skin, usually too small to stitch, there is the potential for complications in any surgical procedure.

The latest technological development is the SudoScan. The nerves controlling the sweat glands in our feet and hands (part of our autonomic nervous system), are usually affected in peripheral neuropathies before those for sensation. These can be evaluated non-invasively, and provide us with objective information, not influenced by the patient’s perspectives, opinions, or preconceived notions. One simply places their hands and feet on the device, and autonomic nerve function is tested, painlessly and silently, with hard data produced. We’re talking numbers, graphs, and charts here.

Once a diagnosis is made, treatment of some sort is recommended but, just as important, education is hugely beneficial. All the experts, including the American Diabetes Association, recognize the benefits of learning about diabetic foot care, what to do and what not to do, to keep your feet healthy. Caring for one’s feet is very different for the diabetic. Through these educational efforts, studies demonstrate a reduction in limb-threatening events. This translates to less major amps (i.e. a foot and part of the leg), and because a major amp is an independent risk factor for death, when we save a limb, we may be saving a life.

Like many conditions, the longer neuropathy is present, the worse it gets. Too often, by the time it is diagnosed, the damage to the tiny skin nerves is extensive and our therapies ineffective. Early diagnosis is key, but rarely obtained. Objective, direct measurements of nerve function and viability, precise and repeatable, are possible and available.

As a healthcare system, we need only recognize the importance of making an early diagnosis of neuropathy, possible with objective information from a thorough evaluation of peripheral small fiber nerve function. If you or a loved one have numbness or tingling in your feet, seek out the specialized tests that can determine if you have peripheral neuropathy.

Editor’s note: Dr. Conway McLean is a physician practicing foot and ankle medicine in the Upper Peninsula. Dr. McLean’s practice, Superior Foot and Ankle Centers, has offices in Marquette and Escanaba, and now the Keweenaw following the recent addition of an office in L’Anse. McLean has lectured internationally, and written dozens of articles on wound care, surgery, and diabetic foot medicine. He is board certified in surgery, wound care, and lower extremity biomechanics.