Measurable deficit of autonomic and sensory nerve function in asymptomatic diabetic patients

Abstract

In a group of 46 consecutive outpatients attending the diabetic clinic of our Metabolic Department, 30 insulin-dependent and 16 non-insulin-dependent diabetic patients in stable metabolic control, and in 38 age-matched controls, we measured vibration perception threshold with biothesiometer and autonomic function, by means of the five classical cardiovascular tests: R-R interval variations during deep breathing, Valsalva ratio, lying-to-standing, postural hypotension, and sustained handgrip. None of the patients complained of symptoms related to diabetic autonomic neuropathy (DAN) or sensory polyneuropathy. Vibration perception threshold positively correlated with Valsalva ratio ( p < 0.05) and deep breathing ( p < 0.01), and all of them correlated with age ( p < 0.001), but not with duration of diabetes and metabolic control. Patients scored significantly lower than controls in vibration perception threshold and all of the autonomic function tests. According to the outcomes of cardiovascular tests [“Autonomic Score” (AS)] patients were divided into two different groups: presence (DAN + = AS≥3) or absence (DAN − = AS<3) of autonomic neuropathy. The DAN − group ( n = 28, 60.9%) showed no significant differences from the DAN + group ( n = 18, 39.1%) in age, duration of diabetes, glycated hemoglobin, or body mass index. DAN + patients had vibration perception threshold measured at the first toe tip and at external malleolus significantly higher than DAN − patients ( p < 0.01 and p < 0.001, respectively) and controls ( p < 0.005), as well as all the other cardiovascular tests except sustained handgrip. No difference in any of these items was observed between DAN − patients and controls. Considering all patients, and assuming a vibration perception threshold value of 95th percentile or greater of age-matched controls as indicative of sensory impairment, we observed a significant association between autonomic and sensitive deficit ( χ 2 = p < 0.01). Our data suggest that in diabetes mellitus, even in the absence of symptoms, there exists a measurable compromission of neurologic function, and that there is an association between autonomic and peripheral neuropathy, even in the early phases of their natural history.