CHICAGO - Abnormal glucose metabolism, which occurs when the body has difficulty processing sugar (glucose) into energy, is twice as common among patients with chronic nerve dysfunction of unknown cause than among the general population and may be a risk factor for the condition, according to a study posted online today that will appear in the August 2006 print issue of Archives of Neurology, one of the JAMA/Archives journals.
Many older adults experience nerve disorders known as neuropathy, some of which are characterized by symptoms of "burning feet" and other unpleasant sensations in the lower leg, according to background information in the article. Diabetes, genetic disorders, exposure to toxic substances and a condition called amyloidosis in which extra protein-based substances accumulate in the body tissues can all cause neuropathy, but many cases do not have an easily identifiable underlying cause. When laboratory tests cannot determine the cause, the condition is known as chronic idiopathic axonal polyneuropathy; a cause is eventually found in only 7 to 30 percent of these cases.
Charlene Hoffman-Snyder, M.S.N., N.P.-B.C., Mayo Clinic, Arizona, and colleagues identified 100 consecutive patients (60 women and 40 men) with chronic idiopathic axonal polyneuropathy who were evaluated between January 2003 and January 2005. Patients underwent a complete neurological evaluation and had a fasting plasma glucose test, which measures the levels of glucose in the blood after eight hours of not eating, and a two-hour oral glucose tolerance test, which determines how well the body processes glucose by drawing blood two hours after fasting patients ingest a dose of glucose. "The fasting plasma glucose level alone does not always identify patients with impaired glucose tolerance and neither does the two-hour oral glucose tolerance test always detect patients with impaired glucose metabolism," the authors write. "Both tests are, however, useful to detect hyperglycemia [high blood sugar] and the consequences of disordered glucose metabolism."
According to the two-hour oral glucose tolerance test, 62 patients (62 percent) with neuropathy had abnormal fasting glucose metabolism, including 24 with undiagnosed diabetes. (This compares with 33 percent of patients of similar ages in the general population with abnormal glucose metabolism as previously estimated by the Centers for Disease Control and Prevention in other published reports.) The results of the current study suggest that abnormal glucose metabolism may be a risk factor for neuropathy.
"Conventional thinking among diabetologists is that diabetic polyneuropathies are the result of prolonged hyperglycemia," the authors write. "Like previous studies, this investigation supports the hypothesis that distal axonal polyneuropathies may occur in much earlier stages of abnormal glucose metabolism than previously thought. Recent studies suggest that the neuropathy associated with impaired glucose tolerance may be milder than neuropathies traditionally associated with diabetes mellitus and may be the earliest detectable sign of abnormal glucose metabolism."