“Visual deficits from aging might prevent someone from seeing a blister or a cut on his foot,” he says. “Loss of flexibility might make it harder to look at the bottom of the feet. Even a diminished sense of smell, a normal part of aging, can prevent someone from smelling an infection.”
Diagnosing peripheral neuropathy
The American Diabetes Association recommends that all people with diabetes have a foot examination every year. Those with diagnosed neuropathy should have a foot examination at every visit with a health professional. That examination should include at least a crude test for loss of sensation, and some professionals believe that more sophisticated tests should be included as well.
There are several relatively simple ways to assess the loss of protective sensation that signals peripheral neuropathy. Among the simplest and easiest to administer is the Semmes-Weinstein 5.07 (10-gram) monofilament test. The monofilament is a piece of nylon that is designed to bend as its tip is pressed against the foot.
The test is simple: the person lies down or sits barefoot, with legs extended and supported. The examiner presses the monofilament against four to ten locations on each foot and records whether the person feels the pressure. The filament bends at 10 grams of force, which can be felt by most people with intact nerve function. A secondary but equally important benefit to the monofilament test is that it causes the examiner to take a close look at the feet.
Vibration testing with a tuning fork is another simple test for loss of sensation. The fork is struck and applied to various parts of the foot or leg. The person having the test reports his perception of both the start of vibration and the cessation of vibration.
A professional can also test pain perception by pricking a person’s skin with a sterile needle.
An annual examination should also include checking pulses in each foot to check the blood supply to the feet. If a problem is found, more complicated studies can be done to pinpoint the cause.
Joseph C. Arezzo, PhD, Professor of Neurology and Neuroscience at the Albert Einstein College of Medicine in New York City, cautions that while the monofilament and other simple tests for sensation have value, they fall short of a complete assessment.
“For a rapid and simple screening, it’s a useful technique,” he says, “but it can only tell you gross abnormality. That’s important because if you’re diabetic and have neuropathy, it’s almost immediately assumed that it’s due to diabetes. In fact, you could have an asymmetric neuropathy, or a slipped disk, or a nerve root disease. In other words, people with diabetes can have anything else that can go wrong with anyone. If you assume the loss of sensation is due to diabetes, you could miss the other problems.”
Diabetic peripheral neuropathy is symmetrical, so Dr. Arezzo says that a screening should determine if the loss of sensation is worse on one side than the other, which might indicate a different condition. Likewise, diabetic peripheral neuropathy is usually worse the further you go toward the foot, so if it is not, that could also indicate the need to look for another problem.
“You need to look at the progression and severity, which can be done as simply as adding different monofilaments that bend at lower forces,” he says, “and you should test not just both feet, but both ankles and both knees.”
The “gold standard” for assessing neuropathy is to assess a person’s electrophysiology by directly measuring nerve conduction and the strength of nerve signals. A nerve conduction study tests the response of muscles to mild electrical shocks, which are delivered through pads placed on the skin. The person indicates when he feels a tingling sensation, which may or may not be painful. A more invasive examination involves inserting thin needles into the muscle to measure the nerve conduction and does not involve electricity. The only pain associated with this test is that of the actual insertion of the needle through the skin.