ROCHESTER, Minn. -- Mayo Clinic researchers have found that subtlechange in nerve conduction is the first reliable sign of nervecomplications from diabetes and that this change can be measured longbefore other symptoms or signs of nerve damage develop.
"We've found what we believe is the earliest sign of nerve change dueto diabetes," says Peter J. Dyck, M.D., Mayo Clinic neurologist andlead researcher on the study. Results were published in the Septemberissue of Diabetes Care. "Changes begin much earlier than previouslydemonstrated," he says.
About 500 patients from Olmsted County, Minn., home to Mayo Clinic,participated in the longitudinal study, many for 20 years. Patientsagreed to periodic measures of their diabetes and measurement of nerve,eye, kidney and blood vessel complications.
About half the people with diabetes develop some type of nerve damage(neuropathy) caused indirectly by high blood sugar levels. Symptoms caninclude pain, asleep-type numbness, tingling, burning and loss offeeling. Serious complications can include foot ulcers, gangrene,amputations, blindness and kidney failure.
In the study, researchers used various techniques to measure nervechanges, including patient exams, reflex and strength tests, and nerveconduction tests, which measure how quickly nerves carry electricalsignals. The nerve conduction tests, over time, provided the mostconsistent and reliable measures of early nerve damage due to diabetes.
"Even when patients had nerve conduction values well within the normalrange, our serial assessments showed steady, unequivocal andstatistically significant worsening," says Dr. Dyck.
The nerve conduction measures were corrected for variations inpatients' age, height and weight that could have affected results.
The study focused especially on 90 patients who at first evaluation didnot have nerve damage and who had been evaluated at least six times atannual or biannual intervals. The Mayo investigators then tested whichmeasure of neuropathy (nerve conductions, symptoms, neurologic signs,quantitative sensation tests or quantitative autonomic tests)significantly worsened, improved or remained unchanged over the studyperiod. Of the five tests, only nerve conduction showed an unequivocal,highly significant, steady worsening over time.
Dr. Dyck says the study offers insights for diabetes care and future research on treatment.
"The aim should be to prevent neuropathy and the complications of eyesand kidneys rather than to intervene after they develop," says Dr.Dyck. Other studies have shown that rigorous control of blood sugar mayprevent and possibly even reverse nerve, eye and kidney complicationsfor people with diabetes.
About 18 million Americans have diabetes. From 60 to 70 percent ofpeople with diabetes develop some type of neuropathy or nerve damagedue to the disease, according to the American Diabetes Association.Assuming that no symptoms means good news is dangerous, according toDr. Dyck. "The study shows that diabetes is insidious from thebeginning," he says. Diabetes is like atherosclerosis and hypertension,which develop insidiously and continuously unless controlled. Later,they may result in such severe problems as strokes, heart attacks andgangrene of the feet and legs.
Mayo Clinic research results could also influence the design of futureclinical trials on treatment options for diabetes. Because nervechanges begin so early, Dr. Dyck says it will be important for clinicaltrials to include less severely affected patients and to performstudies over longer periods.
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