At a podiatry diabetic foot assessment, we use a simple and painless method to check nerve function. The test uses a tool called Semmes Weinstein Monofilaments, which are like small piece of fishing line that are graded to deliver a tough of a particular weight. These are uniformly used all around the world to give consistent measurements.
Neuropathy is a condition that involves a decrease in the ability of your nerves to function properly. It can be brought on by poor blood sugar control or by reduced blood flow to the tissue of the nerves themselves.
There are three types of nerves in the neural system: sensory, motor and autonomic nerves, which we will discuss briefly below. Neuropathy has different though important effects on each kind of nerve which will then affect different functions. Diabetic neuropathy is usually symmetrical – meaning about equal on the left and right side, affects the feet more than it does the hands and is progressive – i.e. it worsens as time passes or as the underlying disease escalates. As it is an absence, more than a presence, of feeling, the condition’s progress is often not noticed. Its importance should not be underestimated because neuropathic changes in the feet is the biggest single predictor of amputations of the foot and leg.
Sensory nerves: These are the nerves that you probably first think of when talking out neuropathy. They report feelings, temperature, touch, pressure and pain sensations back to your brain. Sensory nerve neuropathy can result in a condition known as paraesthesiawhere the brain is tricked into interpreting ordinary sensations as being painful or annoying. When this occurs, it is most often worse at night and while resting and is relieved by moving around. People with this sort of neuropathy can often get some respite from the sensations by giving the nerves something real to report back to the brain. Roughly textured socks, fleecy mats or electrostimulation / TENS devices may help.
Sensory neuropathy can also cause a different deficit called anaesthesia, where sensations are dulled or not felt at all. This is obviously not painful but position sense and balance can be markedly affected. Sensory neuropathy also makes injury to the foot or feet much more likely as your normal protective defenses are lessened. Remember as a child standing on the beach how you had to move quickly to avoid the pain the hot sand could bring? Without sensation, feet can be badly burned in what should be a simple walk for pleasure. Sensory neuropathy can lead to problems where an injury may not be noticed and therefore not cared for. Imagine having a thorn in the skin of the sole which could be walked on for days, driving an infection deeper into the tissue. Neuropathy can also keep your immune and repair systems from properly detecting an injury and sending white blood cells to fight infection or repair a breach in the skin.
Motor nerves: Neuropathy affecting the motor nerves responsible for movement can cause the muscles they should supply to wither and waste away. This can which causes muscle imbalances and deformities which may make bone or joints more prominent and cause potential pressure areas . This is one reason why clawing toes are very often associated with the diabetic foot. Your gait pattern or walking style may also change with motor neuropathy and areas of heightened pressure are likely to occur in specific areas on the soles of the feet.
Autonomic nerves: The autonomic nervous system controls the things you don’t have to think about, like beating your heart or salivating when food arrives. In your feet, these nerves control many functions, such as sweat glands, blood flow rate and the marshaling of healing resources where wounds are detected. A few examples of how this type of neuropathy can affect the feet include the following. Lacking the ability to sweat effectively leaves the feet dry, cracked and open to splitting and therefore to allowing bacteria to get past the outer layers and into the flesh. The fibrous and fatty layer below the skin, which should act as a cushioning protector, thins. If blood flow is not properly controlled by opening and closing vessels via the autonomic nervous system, the blood can take a ‘shortcut’ that causes underperfusion of the toes meaning a lack of oxygen to that skin and tissue which puts it at risk of non healing. Veins may also appear prominent and oedematous swelling may be present.
To read this Q&A session about diabetic foot conditions as a single handbook, or to access the downloadable / printable version, please browse to our Diabetes Info Sheet. Alternatively, use this link to return to the Podiatry FAQs Blog.