Diabetic neuropathy: a cross-sectional study of the relationships among tests of neurophysiology

OBJECTIVE — To determine the relationships among large, small, and autonomic fiber neurophysiological measures in a cross-sectional study of patients with diabetes. RESEARCH DESIGN AND METHODS — We assessed 130 individuals: 25 healthy subjects and 105 subjects with diabetes. Subjects were classified by the presence or absence of neuropathy by physical examination. All subjects underwent autonomic testing, nerve conduc-tion studies, quantitative sensory testing, and nerve-axon reflex vasodilation in addition to quantifiable neurological examination and symptom scores. Correlation and cluster analysis were used to determine relationships between and among different neurophysiological testing parameters. RESULTS — Results of neurophysiological tests were abnormal in patients with clinical evi-dence of diabetic neuropathy compared with results in healthy control subjects and in those without neuropathy (P 0.01, all tests). The correlations among individual tests varied widely, both within (r range0.5–0.9, NS to0.001) and between test groups (r range0.2–0.5, NS to0.01). A two-step hierarchical cluster analysis revealed that neurophysiological tests do not aggregate by typical “small, ” “large, ” or “autonomic ” nerve fiber subtypes