Could slightly high blood sugar cause neuropathy?

Conditions Expert Dr. Otis Brawley Chief Medical Officer,
American Cancer Society

Expert answer

Dear Terry, Thanks for your question.

I like to think of blood glucose values as a spectrum of numbers with no clear cutoff between nondiabetic and diabetic. In similar manner there is a gray area of blood glucose that defines pre-diabetes. Many people use blood sugar and blood glucose interchangeably.

The definition of diabetes has changed over time. The numbers you quote might very well be considered diagnostic of diabetes today whereas they were not 20 years ago. In 1997, the American Diabetes Association definition of normal blood glucose decreased from 120 to 110 mg/dL (6.1 mmol/L). In 2002, the American Diabetes Association defined a normal fasting blood glucose as less than 100 mg/dL (5.6 mmol/L).

Today we consider fasting blood sugars of 100 mg/dl to 125mg/dl to be in the realm of glucose intolerance which is sometimes called pre-diabetes. These patients are at increased risk for developing frank diabetes. Several fasting glucose levels over 125 or a single random glucose over 200 mg are considered diagnostic of diabetes.

There are other tests used to make the diagnosis of pre-diabetes or diabetes. Pre-diabetes is defined as a blood sugar of 140 to 199 mg/dL (7.8 to 11.0 mmol/L) two-hour after drinking 75 grams of an oral glucose solution. The diagnosis of diabetes is confirmed with a blood sugar of 200 mg/dL or greater, two hours after ingestion of the glucose solution. Hemoglobin A1C is a blood test that gives an estimate of blood sugar levels over the previous three months. Persons with a value of 5.7 to 6.4 percent are thought to have pre-diabetes. Those with a value of 6.5 percent or higher are considered diabetic.

About 30 percent of patients with frank diabetes for more than a decade have some neuropathy. It usually presents as numbness, itching or tingling in the legs but can also be pains. It can even present as digestive problems such as difficulty digesting food or diarrhea due to problems with nerves in the bowels. Most diabetic neuropathy is caused by peripheral artery disease, in which the small blood vessels are obstructed or partially obstructed and cannot carry oxygenated blood to areas of the body. These areas have pain or other difficulties due to the lack of oxygen.

It is very possible for someone with numbers that are considered pre-diabetes to have some of the complications of diabetes This is especially true of big vessel disease such as myocardial infarction (heart attack), stroke and peripheral vascular disease. Retinopathy, neuropathy and kidney disease are rarer in pre-diabetics but can occur, especially in someone who has pre-diabetes and hypertension (high blood pressure). The condition of pre-diabetes combined with hypertension is often referred to as the "metabolic syndrome." Elevated cholesterol and triglyceride combined with diabetes and hypertension increases risk of neuropathy even further. Of note, there are some nondiabetics with neuropathy and peripheral vascular disease caused by elevated cholesterol and triglycerides only.

It is prudent that you have a relationship with a physician who will measure not just blood sugar, but cholesterols, triglycerides and blood pressure. He or she may decide that lowering your blood sugars through diet or medication or both might be beneficial for your long-term health. Lowering blood sugar can sometimes even better the pain of diabetic neuropathy. Many pre-diabetics and diabetic patients are also treated for cholesterol and triglyceride problems and get a baby aspirin daily to decrease risk of heart disease. There are also a number of treatments for pain caused by neuropathy.

In addition to having the above tests, people with pre-diabetes and diabetes should get an annual eye examination to rule out early diabetic retinopathy. Diabetic retinopathy is treatable and is the most common cause of blindness. It is also prudent to examine the feet for wounds that the patient might not appreciate due to loss of sensation as a part of diabetic neuropathy. Assessment of kidney function and some studies of the heart and vascular system may also be called for.

By the way, there are other causes of peripheral neuropathy. Not uncommon are amyloidosis, which is a disease in which excess protein is deposited in nerve tissue, and vasculitic neuropathy, a rheumatologic disease in which the patient has inflammation near the nerve. Also we must consider alcoholic neuropathy in someone with an extreme drinking history and even lead poisoning as a possible cause. Patients who have been treated with chemotherapy for cancer and some rheumatologic diseases can also get some painful neuropathies.