Damage to nerves. In people with diabetes, neuropathy is generally caused by high blood sugar levels, but there are other possible causes of neuropathy, such as a B vitamin deficiency, injury, some drugs, and cancer.
Excess glucose from the blood can infiltrate the nerves, interfering with their function by disrupting the electrical impulses they carry. Depending on which nerves are affected, neuropathy takes two main forms: sensory neuropathy and autonomic neuropathy.
Sensory neuropathy affects the sensory nerves, the nerves responsible for sensation throughout the body. It most commonly affects the feet, legs, hands, and arms. The symptoms may include numbness or a loss of sensation, coldness, tingling, burning, and extreme sensitivity to touch. Sensory neuropathy, especially in the feet, can cause people to be unaware of an injury, which, in conjunction with poor wound healing, can set the stage for a foot ulcer.
Autonomic neuropathy affects the nerves that control the involuntary functions of the internal organs. Depending on the exact nerves affected, autonomic neuropathy can cause the following problems:
- When it affects the cardiovascular system, autonomic neuropathy can cause heart attack, rapid heartbeat at rest (when you are sitting or lying down), very high blood pressure during exercise, and a condition called orthostatic hypotension. (Orthostatic hypotension is caused by damage to the nerves that control contraction of the blood vessels. It is characterized by a drop in blood pressure when a person stands up or sits up from a lying position, causing weakness or dizziness.) Autonomic neuropathy can also cause the nerves to the heart to fail to speed up or slow down the heart rate in response to exercise.
- When the nerves controlling the stomach are affected, a condition known as diabetic gastroparesis may result. In this condition, the movement of food through the stomach is slowed or even stopped, which can cause nausea and vomiting. In addition, by disrupting the timing of food absorption, gastroparesis can seriously disrupt blood sugar control.
- Autonomic neuropathy can affect the bladder, making it difficult to tell when it is full, sometimes leading to urinary incontinence.
- It can cause sexual dysfunction, especially in men. Nearly half of all men with diabetes develop impotence. In some cases, this may be caused by damage to the nerves affecting blood flow to the penis.
Maintaining near-normal blood sugar levels can help prevent and treat both sensory and autonomic neuropathy. For painful sensory neuropathy, your doctor may recommend a number of pain relievers, such as aspirin, acetaminophen, or one of the nonsteroidal anti-inflammatory drugs. Pain may also be relieved by tricyclic antidepressants such as amitriptyline or anticonvulsants such as gabapentin (brand name Neurontin). Other, nonmedical treatments such as biofeedback, guided imagery, and meditation may also be helpful to some people.
One of the most promising new treatments for painful sensory neuropathy is an over-the-counter cream, sold under various brand names, that contains capsaicin. Capsaicin, found naturally in red peppers, has been used for centuries as an herbal pain remedy. Research shows that it depletes substance P, a neurotransmitter responsible for signaling pain, in the peripheral nerve endings (those in the feet, hands, legs, and arms). Studies show that it may relieve symptoms in about half of people taking it. The rest either show no improvement or, in a few cases, worsening of their symptoms. Speak with your doctor before trying this or any other over-the-counter pain product.