Evaluation of autonomic neuropathy in diabetes mellitus. Comparison of clinical, functional and biochemical parameters.

Quantitative assessment of signs or symptoms of neuropathy, and the beat-to-beat variation, valsalva, orthostasis, handgrip and cold pressor tests, and measurements of plasma renin and catecholamine excretion rate were performed in 23 diabetic patients and 10 age-matched normal subjects. Significant inverse correlations were found between the clinical score and the beat-to-beat variation (a test of efferent vagus function) (r=-0.55, -0.72, P less than 0.0005) or the pressor response to handgrip (possible test of efferent sympathetic integrity (r=p less than 0.005) or the values of both tests combined (r=-0.79, P less than 0.0005); but not with the other measured parameters. Beat-to-beat variation was abnormal in all 9 diabetics with increased and in 9 of 14 with normal clinical score, whereas only seven and one patient from these subgroups, respectively, had an abnormal Valsalva ratio. The pressor response to handgrip was only slightly reduced in the diabetic patients, with greater tendency in those with abnormal clinical score. Additional possible indices of adrenergic dysfunction such as the pressor response to cold stimulus, plasma renin levels and noradrenaline or adrenaline excretion rates did not differ significantly between normal subjects and diabetics. These finding demonstrate a greater prevalence of parasympathetic as compared to sympathetic impairment in diabetic autonomic neuropathy; the beat-to-beat variation was the most sensitive among the tests used. An assessment of clinical evidence combined with non-invasive functional procedures such as the beat-to-beat variation and handgrip tests provide a valuable and easy to perform tool in the evaluation of diabetic neuropathy.