According to the American Diabetes Association, about 15.7 million people (5.9 percent of the United States population) have diabetes. Nervous system damage (also called neuropathy) affects about 60 to 70 percent of people with diabetes and is a major complication that may cause diabetics to lose feeling in their feet or hands. Foot problems are a big risk in diabetics. Diabetics must constantly monitor their feet or face severe consequences, including amputation.
Diabetics lose feeling in their feet. This is called diabetic sensory neuropathy. Grossly simplified, the nerves do not conduct sensations as well as they can. This is due to a variety of factors, but commonly a higher level of sugar in the blood stream diminishes the nerve action potential. Direct metabolic damage then occurs to the nerves, which results in neuropathy. There are three types of neuropathies a diabetic can have. Sensory, motor, and autonomic neuropathies are all possible. Sensory neuropathy, the most common type, usually presents as the first type before motor neuropathy. It is classically described as a sock and glove distribution. This means than the loss of sensation occurs in the same distribution as a sock. That is, all feeling is lost or diminished below a certain level just above the ankle joint, in the same area where a sock would be around the lower leg. A diabetic will not be able to detect sensation or will have difficulty detecting two points of discrimination. A person can also have an absent protective threshold. In other words, a diabetic may not be able to feel hot water when checking drawn bath water, whereas a non-diabetic would jump, pull their hand back reflexively, and say "ow!" This example also clearly illustrates the lack of temperature discrimination. Another sequella is diminished vibration sensation.
Lastly, proprioception can also be affected. Proprioception is the ability of the body to know where a limb is in space or what movement is being performed. For example, when you close your eyes while walking over a curb, your bodys’ own sensing system takes over. It knows just how much height is required to lift the foot over the curb. It also knows when to expect your foot to land onto the ground above the curb and at what force should be expected. We are able to perform this complex task because of small receptors that line our joints and detect tiny movements made by us. These movements are interpreted by our brains like movement in space. Motor neuropathy is a deficit of motor coordination affecting the intrinsic muscles of the foot leading to biomechanical and structural changes of the foot. These changes predispose the diabetics feet to ulcers and subsequent infections. Another type of neuropathy that can occur is autonomic neuropathy. The autonomic nervous system is responsible for regulating body temperature among other things. It does this by creating sweat and directing blood flow to or away from an extremity. Poor control would lead to reduced blood flow, lack of sweating, and other conditions. It also is responsible for hair follicles reacting to reduce heat or gather warmth.