Sympathetic neural abnormalities in type 1 and type 2 diabetes: a systematic review and meta-analysis

Background:Microneurographic recordings of muscle sympathetic nerve activity (MSNA) have shown that sympathetic activation may characterize diabetes mellitus. However, it is recognized that comorbidities and metabolic abnormalities frequently associated with both type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) diabetes affect MSNA, generating potential confounding effects and making the association between sympathetic activation and diabetes mellitus still a controversial matter.Methods:The present meta-analysis evaluated 11 microneurographic studies enrolling 314 diabetes mellitus patients and healthy controls, and MSNA was chosen as the main variable of interest. Collection of the data included indirect adrenergic markers such as heart rate and venous plasma noradrenaline, together with hemodynamic, anthropometric and metabolic variables.Results:A total of 11 microneurographic studies were evaluated including 314 diabetes mellitus patients and controls. Diabetes mellitus displayed MSNA significantly greater than controls (mean difference amounting to 8.1, 95% confidence interval 1.21-15.08, P<0.05). This difference was ascribed to T2DM, since T1DM patients displayed MSNA values superimposable to controls. In T2DM MSNA was directly related to age (r=0.83, β=0.82, P<0.04) and plasma insulin (r=1.00, β=2.25, P<0.01) but not to other variables.Conclusion:T2DM-related sympathetic activation is detectable even when obesity, hypertension and metabolic syndrome are excluded; not found in T1DM; not associated with anthropometric and hemodynamic variables; and related to plasma insulin.