Neuropathy, which refers to nerve damage, is a common complication of diabetes. Almost a quarter of people with type 2 diabetes have nerve damage at the time they are diagnosed and up to 50% will eventually develop some type of neuropathy.1,2
What goes wrong in diabetic neuropathy
To understand what goes wrong in diabetic neuropathy, you need to understand a few basics about the nervous system. The nerves in the body are made up of cells called neurons. These neuron include a dendrite (the word means tree in Greek) that receives or conducts electrical stimulation from other nerves cells in the body and an axon, the long fiber that project away from the neuron and are responsible for transmitting electrical impulses from neuron to neuron as well as muscles and organs in the body. The axon is covered with a fatty substance called myelin, which acts like a protective cover (like the plastic cover on an electrical wire).
Think of the nervous system as all the electrical wiring in your home (this includes your telephone, cable, and other wiring systems). We depend on this wiring and the electricity and other signals it carries for all of the basic necessities and conveniences that we are accustomed to having in our homes, from lighting, appliances, and heating and cooling, to television, telephone, and even the home security systems that keep us safe. Our nerves are designed to transmit electrical impulses to carry out all sorts of jobs that help the body function, from providing us with the sensation of touch and heat and cold, to taking care of automatic body functions that keep working without our thinking about it (like the heart or lungs), to active control of our muscles for locomotion or fine muscle control.
Although we don’t have the complete picture of what goes wrong in diabetic neuropathy, we think the axons becomes damaged. Damage to axons may come from a reduction in the blood supply to the nerve cell or from harmful substances called toxins that are produced when the body metabolizes high levels of blood glucose. Axon damage results in a slowing of the speed at which an electrical impulse can travel along a nerve fiber (similar to the way in which an old electrical wire that is partially broken is no longer an efficient means of carrying electricity). A key test for diabetic neuropathy involving nerves of sensation and movement measures nerve conduction velocity (NCV)1
As in so many complications related to diabetes, high blood glucose appears to play a central role in diabetic neuropathies. Typically diabetic neuropathy develops in people in whom blood sugar uncontrolled or more than 10 years. Controlling blood sugar can improve symptoms and, in some cases, even resolve neuropathy.3
Different types of diabetic neuropathy
There are several different types of neuropathy that affect people with diabetes. These neuropathies are classified according to which part of the nervous system is affected and how it is affected. Diabetic neuropathies can be categorized into four groups2:
- Disorders of sensation
- Disorders of autonomic nerves
- Disorders of movement
- Disorders of nerve entrapment
Disorders of sensation
Disorders involving abnormal nerve sensations (often pain) are the most common forms of neuropathy associated with diabetes. They arise from damage to sensory nerves, those nerves responsible for carrying signals that alert us to sensations, including pain, heat, and cold.
Distal polyneuropathy. The most common type of diabetic neuropathy, distal polyneuropathy involves abnormal sensation in the hands and feet (distal is a Latin word that means away from the center). Distal polyneuropathy (also called peripheral neuropathy) can be dangerous because a person may experience an injury, such as a burn or cut on the foot, and not be aware due to abnormality of sensation. The signs and symptoms of distal polyneuropathy include:
- Tingling and burning sensation
- Extreme sensitivity to touch
- Inability to feel light touch or determine the position of the foot
- Decreased ability to sense pain and temperature
- Weakness and loss of balance
Learn more about distal polyneuropathy
Radiculopathy nerve-root involvement. This disorder is associated with severe pain, affecting one side of the chest or abdomen, resulting from damage to the root of the nerve as it leaves the spinal column. Pain may persist for anywhere from 6 to 24 months. Control of blood sugar and standard pain management can be useful.
Polyradiculopathy-diabetic amyotrophy. P. Polyradiculopathy-diabetic amyotrophy involves a combination of loss of muscular strength, affecting the upper part of the leg, and pain, extending from the hip to the thigh. A person who experiences this disorder may not able to extend or straighten the knee due to loss of muscular strength. Unfortunately, this disorder tends not to improve with increased blood glucose control. Typically, it lasts only a short time, but in some cases it can persist for years.
Disorders of the autonomic nerves
The autonomic nervous system is the system of nerves that is responsible for the function of muscles that work without our having to think about them. Autonomic is related to the word automatic and a variety of muscles and associated organs are controlled by autonomic nerves, from our heart and lungs to our stomach and intestines, work automatically. As many as 40% of people with diabetes may be affected by some type of autonomic neuropathy, including4:
- Bladder dysfunction
- Intestinal abnormalities
- Heart abnormalities
- Vision problems
Learn more about disorders of the autonomic nerves
Disorders of movement (mononeuropathy)
Diabetic neuropathy can affect the function of nerves that control various muscles in our body, including those involved in movement. Movement disorders (also called mononeuropathies) happen when damage occurs to the motor nerves that carry electrical impulses that tell our muscles to move. We think that these types of disorders result from a sudden blockage or closing off of a blood vessel that feeds a specific motor nerve. Mononeuropathies can affect motor nerves in various parts of the body, from the face (including the eyes) to those in upper and lower extremities. There are at present no effective treatments for mononeuropathies. However, these disorders typically resolve on their own after several months.2
Disorders of nerve entrapment
Disorders of nerve entrapment (also called entrapment neuropathies) occur when individual nerves become swollen and inflamed and are squeezed as they pass through areas of the body where there are structures made of bone and ligament. Entrapment neuropathies are common complications associated with diabetes, affecting as many as one-third of people with diabetes. They may include5,6:
- Carpal tunnel syndrome
- Tarsal tunnel syndrome
- Ulnar entrapment
- Peroneal entrapment
- Radial nerve entrapment
Learn more about disorders of nerve entrapment