Diabetic Autonomic Neuropathy

Abstract & Commentary

Synopsis: These findings indicate that autonomic symptoms and deficits are common in diabetes, but mild in severity, and that the correlation between symptom scores and deficits is overall weak in mild diabetic neuropathy, emphasizing the need to separately evaluate autonomic symptoms.

Source: Low PA, et al. Autonomic Symptoms and Diabetic Neuropathy: A Population-Based Study. Diabetes Care. 2004;27:2942-2947.

Diabetic patients (n = 231) enrolled in the Rochester Diabetic Neuropathy Study at the Mayo Clinic, and healthy controls (n = 245) underwent comprehensive autonomic function evaluation to determine the prevalence of autonomic dysfunction in multiple organ systems in diabetes. Ninety-nine percent of the diabetics were white, approximately half were men, and overall mean age was 59.4. Type 2 diabetics, as a subgroup, were older than type 1 patients, with a mean age of 64.1 vs 50.9 years. Normal controls were of comparable age and sex to the patient group. Evaluations undertaken included an Autonomic Symptom Profile (ASP) and a Composite Autonomic Severity Score (CASS). ASP comprises 169 questions covering 11 domains, including orthostatic intolerance, secretomotor, urinary, diarrhea, constipation, sleep, pupillomotor, male sexual failure, vasomotor, upper gastrointestinal symptoms, and syncope. Self-reported, ASP is designed to provide an indication of the severity of dysautonomia. CASS is a battery of autonomic reflex tests, including sudomotor axon-reflex testing, beat-to-beat blood pressure, and heart rate in response to head-up tilt, and Valsalva maneuver and heart rate response to deep breathing. Data was analyzed using 1-way analysis of variance, Kruskal-Wallis, Mann-Whitney U tests, Bonferroni corrections, and Spearman correlations.

Autonomic dysfunction was found in 54% and 73% of type 1 and 2 diabetics, respectively. However, the degree of dysfunction was mild, with mean CASS 2.3 (maximum 10) and only 14% with a CASS of 5 or more, indicating more severe autonomic involvement. Secretomotor, pupillomotor, and sexual failure in men were the only domains where type 1 patients differed from controls, while type 2 patients differed significantly in 9 domains, with only constipation and syncope showing no difference. Comparing type 1 and 2 patients, the latter demonstrated greater problems with diarrhea and urinary domains on the ASP, and cardiovagal abnormalities on CASS. Peripheral neuropathy and autonomic neuropathy occurred in similar percentages. Autonomic neuropathy is common in diabetes but mild in severity.

Commentary

In a separate study performed by a group in Sweden, Type 1 (n = 43) and type 2 (n = 17) diabetics were examined to determine the frequency of sympathetic and parasympathetic neuropathy in these patients. Laser Doppler perfusion of a heated finger was used to measure the vasoconstriction index (VCI), a sympathetic nerve function, and R-R interval (RRI) during deep breathing provided an index of parasympathetic function. Spearman’s correlation coefficient, Wilcoxon’s signed rank, t test, and Fisher’s test provided statistical analysis.

Sympathetic function (VCI) was abnormal in an equal percentage of type 1 (40%; n = 17) and type 2 (41%; n = 7) patients, but parasympathetic function (RRI) was significantly more prevalent in type 2 (65%; n = 11), compared to type 1 (42%; n = 18) diabetics. Twenty-three percent (n = 10) of type 1 and 29% (n = 5) of type 2 patients had abnormalities of both measurements, but these correlated only in the former (P = 0.0002 vs 0.97, respectively). Sympathetic and parasympathetic dysfunction is frequent among both diabetic groups, but a correlation between the 2 is seen only in type 1. Michael Rubin

Dr. Rubin, Professor of Clinical Neurology, New York Presbyterian Hospital-Cornell Campus, is Assistant Editor of Neurology Alert.