The high blood sugar from diabetes affects the nerves and over time increases a person's risk for nerve damage. Keeping blood sugar levels within the target range recommended by your doctor helps prevent diabetic neuropathy.
The most common type of nerve disease (neuropathy) affects both sensory nerves, which send information to the spinal cord and brain, and motor nerves, which relay impulses from the brain and spinal cord to move muscles. This is called diabetic peripheral neuropathy.
Diabetes also affects the nerves that control involuntary body functions, such as digestion. This is called diabetic autonomic neuropathy.
Diabetes can affect single nerves. This is called diabetic focal neuropathy.
Diabetic peripheral neuropathy
With peripheral neuropathy, people experience a decrease in sensation or even numbness as well as trouble moving the feet and, later on, the fingers and hands. As a result of this neuropathy, many people with diabetes can't feel when they have injured their feet, and they may not know if calluses or ulcers form. Because of the risk of serious foot injury and infection, it is very important that people with diabetes learn how to examine their feet daily, wear shoes that fit well, and protect their feet from injury.
Diabetic autonomic neuropathy
Diabetes can affect the autonomic nervous system, which are nerves that we can't consciously control. The autonomic nervous system controls many aspects of the body's functioning, such as heart rate and blood pressure, the workings of the gastrointestinal system, and sexual function.
When the autonomic nerves regulating the heart and blood vessels are affected, a person's heart rate and blood pressure may go up and down abnormally or may not rise appropriately in response to a stimulus such as exercise. Sometimes, people who have diabetes can experience fainting spells because their blood pressure drops rapidly.
The autonomic nerves affecting the gastrointestinal (GI) system control the way these organs contract and relax in order to move food along. When the nerves that cause the stomach to contract and move food are affected, it is called diabetic gastroparesis. Sometimes the effects on the GI system becomes so severe that a person has to be fed through a feeding tube placed in the small intestine, bypassing the stomach. When diabetes damages these nerves, a wide range of symptoms can result, including:
A sensation of food getting stuck because of problems with how the esophagus contracts and relaxes.
Nausea and vomiting because of problems with the stomach.
Alternating constipation and diarrhea because of abnormal functioning of the large intestine.
Occasionally, fecal incontinence.
When the urinary system is affected, emptying of the bladder may be delayed or incomplete. This increases the chances of developing a urinary tract infection. Severely prolonged bladder emptying (urinary retention) can lead to urinary incontinence and, sometimes, fluid backup into the kidneys.
When the nerves in the sexual organs are affected, sexual troubles develop. Diabetes can cause problems in the autonomic nerves that allow a man to achieve an erection and ejaculate. Women may experience vaginal dryness.
Diabetic focal neuropathy
Sometimes, single nerves can be affected by diabetes (focal neuropathy). These nerves may be peripheral, such as the nerves in the legs and arms, or cranial, such as the nerves that control eye movements.
When single nerves become affected, the result is weakness or paralysis of the muscles controlled by the nerves. Usually these motor nerve neuropathies resolve by themselves over a period of several months.