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Diabetes and the Nervous System: How Neuropathy Develops and How It Can Be Treated
Dr. Wiley is Professor, Internal Medicine and Director, Michigan Clinical Research Unit, and Dr. Towns is Research Assistant Professor, Department of Internal Medicine, Division of Gastroenterology, University of Michigan Medical School, Ann Arbor, MI.
Diabetes, formally known as diabetes mellitus, affects 171 million people worldwide, according to the World Health Organization. Type I diabetes usually starts in childhood or early adulthood, while the onset of type 2 diabetes is typically much later, often in middle-age.
Diabetes affects many of the body’s systems and functions, not the least of which may be the nervous system. When the nervous system is affected, diabetic neuropathy can result. This occurs when too much sugar (hyperglycemia) circulates in the blood stream over a long period of time.
It is thought that 60-70% of people with diabetes will develop some form of neuropathy over their lifetimes. While it is still somewhat unclear, diabetic neuropathy tends to occur after about five years of high blood sugar, and it usually peaks after about 25 years. Some people with neuropathy may not have any symptoms at all, while others will experience pain, tingling, or numbness in their hands, arms, feet, or legs. Diabetic neuropathy can also affect different organ systems, including the cardiovascular, genital-urinary, digestive, and vision.(1)
Though the origin of type 1 and type 2 diabetes is different, the result is the same: chronically high blood sugar.(2) And the long-term effects of high blood sugar can be felt in different ways throughout the body, like increasing oxidative stress (damage to cells) of various organs and the overactivation of other metabolic pathways.(3)(4)
All these effects can lead to problems in the ways that nerve cells (neurons) function. And when neurons don’t functions properly, neuropathy can occur. Neuropathy may affect different parts of the nervous system, including the peripheral nervous system (which is made up of all the nerves outside of the brain and spinal cord, including "automatic" or involuntary processes like heart rate and digestion, and all the nerves that provide us with our sense of touch). This article will outline the symptoms of diabetic neuropathy, as well as how it is diagnosed, and the available treatment options.
Signs and Symptoms of Diabetic Neuropathy
The symptoms of neuropathy that diabetic patients may experience vary, depending on which nerves are involved.(5) For example, many patients will first notice numbness, tingling, or pain in the feet. These symptoms are usually mild in the beginning but may worsen over the years, and then actually decrease in later years, as the nerve damage gets worse. Some people report muscle weakness in their hands or feet, while others have problems in their autonomic or involuntary nervous systems. This can show up in a variety of ways, such as constipation, diarrhea, nausea with or without vomiting, feeling full after eating, dizziness with or without fainting related to a drop in blood pressure after standing or sitting up, erectile problems in men, and vaginal dryness in women, and problems with urination. In other words, there are many different symptoms that may signal that nerve damage as a consequence of diabetes is occuring.
Signs of Peripheral NeuropathyNeuropathy of the peripheral nervous system usually begins with tingling or numbness in both hands or feet, which may progress "inwards" over time (in other words, it can begin in the fingertips or toes and proceed up the hands and arms or legs). Some people report that their sensations are "hypersensitive", while other report feeling less sensitivity. This difference may depend on how long diabetes has been present. Some individuals will present with problems involving specific nerves and muscles, for example, double vision, pain or weakness in the face, thigh, chest or abdomen.
Signs of Autonomic NeuropathyAs mentioned, autonomic neuropathy involves the branch of the nervous system that controls the heart and blood vessels, the gastrointestinal tract and genital-urinary system, and the system that monitors and balances blood glucose levels after a low blood sugar (hypoglycemic) episodes.
Patients with autonomic neuropathy may be unaware of the heart palpitations, shakiness, and sweating that can occur with episodes of low blood sugar. When nerves that supply the heart and blood vessels are affected, individuals may lose their ability to adjust blood pressure and heart rate when they change in position, which can result in light-headedness and, sometimes, loss of consciousness.
When the gastrointestinal tract is involved, constipation is often a person's first complaint. Later, some people may experience diarrhea associated with bacterial overgrowth in the small intestine or (rarely) large amounts of diarrhea. When the upper GI tract is affected, it can result in nausea with or without vomiting, loss of appetite with bloating of the abdomen, distention, and feeling particularly full after eating sometime even a small amount, and problems swallowing. This constellation of symptoms can be seen in patients who have slow emptying of the stomach, a condition called gastroparesis.
Autonomic neuropathy may also affect a patient’s urinary tract or sexual function. Some patients may not be able to empty their bladders completely, which increases the risk for urinary tract infections. Some people may also experience urinary incontinence (leaking of urine between bathroom visits). Men may have problems with erections, ejaculation, and orgasm, while women may experience problems with arousal, vaginal dryness, and having a normal orgasm.
People with autonomic neuropathy may also develop an abnormal sweat response, which can result in problems regulating body temperature or producing too much sweat at inappropriate times. Vision can be affected as a result of changes in how the pupil responds to light or in the muscles that coordinate eye movements, which can result in blurry or double vision.
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