Diabetic Autonomic Neuropathy

by Ronald Chusid, D.O.

Damage to the autonomic nervous system due to diabetes is a common, but rarely discussed complication. The autonomic nervous system regulates the internal organs of the body. As with other diabetic complications, at the onset there are no symptoms and diabetics are unaware of the developing damage. Studies have shown that 20% to 40% of diabetic have damage to the autonomic nervous system. It is one of the earliest systems to show effects of diabetes upon testing, but generally there aren’t obvious symptoms until late in the disease.

As the autonomic nervous system is involved with regulation of extensive parts of the body, there are many types of symptoms as the neuropathy becomes advanced. Following are examples of symptoms caused by autonomic neuropathy:

The Heart:

Abnormalities in regulation of heart rate initially cause an elevated heart rate. Poor toleration of exercise can result from inability to increase output of blood as needed for exercise. The circulatory system may not compensate for standing, causing a decrease blood pressure and dizziness with standing (known as orthostatic hypotension). There is an increased risk of heart attacks and sudden death. One study of patients with autonomic neuropathy showed a mortality rate of 56% over five years.

The Gastrointestinal System:

Impairment of the nerves regulating the digestive system can cause symptoms including impaired appetite, gas, nausea, vomiting, reflux, constipation, and diarrhea.

The Genitourinary System:

Autonomic neuropathy can cause bladder abnormalities with problems such as incontinence, urgency, dribbling, and, in extreme cases, inability to urinate. Autonomic neuropathy can also result in impotence in men.

Sudomotor Dysfunction:

Sudomotor dysfunction means abnormalities in sweating and hydration of the skin. Diabetic autonomic neuropathy results in some areas with excessive sweating, while other areas are excessively dry. Most often there is excessive sweating in the face and trunk, and dryness in the legs. The excessive sweating often occurs at mealtime, at night, or with stress. Sometimes it can be mistaken for hypoglycemic reactions. (Conversely, autonomic neuropathy can also reduce early symptoms of hypoglycemia, making diabetics unaware of it until symptoms are severe.)

Testing of diabetic autonomic neuropathy was studied at a joint conference of the American Diabetes Association and the American Academy of Neurology in 1988. They recommended various tests to screen for diabetic neuropathy and the ADA has adopted this as a consensus statement in their annual recommendations for diabetic care. Tests for diabetic autonomic neuropathy generally involve variations in heart rate with various stimuli. This is done because such measurements can often be made in a noninvasive manner with minimal discomfort to the patient, because they can be replicated on repeat tests to show they are valid measurements of the autonomic nervous system, and because when there are alterations to the autonomic nerves regulating the heart, there are generally also similar abnormalities in other areas of the autonomic nervous system.

In my office we generally use two tests to evaluate autonomic reflexes involving the heart. While hooked up to an EKG machine, patients are instructed to breathe extremely slowly. Normally there should be an increased heart rate with breathing in deeply, and a slowing of the heart rate with breathing out. If the nerves which regulate heart rate are affected by diabetes, there may be abnormalities in this pattern. The second test is to have the patient stand up from a lying position. Normally there will be an maximal increase in heart rate at about fifteen beats after standing, followed by a reduction in heart rate to a low level after thirty beats. Absence of this pattern can also indicate damage to the autonomic nervous system. Other tests can also be done including monitoring heart rate response to blowing out strongly, or measuring blood pressure changes with sustained use of a handgrip.

As with other diabetic complications, the best treatment is prevention. Once neuropathies develop, they will sometimes improve with improvement in diabetic control. Various medications are often used to treat symptoms of diabetic autonomic neuropathy. For example, Reglan and Propulsid will often help with some of the gastrointestinal symptoms. Certain antibiotics often help with diarrhea due to autonomic neuropathy. Florinef can help with postural hypotension. A variety of treatments are often used for bladder and sexual complications. Viagra is often helpful for sexual dysfunction regardless of the cause. Due to the increased cardiac risk, many diabetologists recommend annual evaluations of cardiac reflexes using tests mentioned above, with further cardiac monitoring in those with abnormal studies.

Updated November 27, 1999

Dr. Chusid has practiced Internal Medicine in Muskegon since 1985, and has held positions including Chairman of the Department of Medicine and Chairman of the Critical Care Committee at Muskegon General Hospital. He is also an Assistant Clinical Professor of Medicine at Michigan State University, Medical Director of IHS Home Care and a member of the Council of Complications of the American Diabetes Association. His office is located at 1762 E. Oak Avenue, Muskegon, Michigan. Phone (231) 773-3258.