Correlation between sudomotor function, sweat gland duct size and corneal nerve fiber pathology in patients with type 2 diabetes mellitus

AIMS/INTRODUCTION To study the correlation between sudomotor function, sweat gland duct size and corneal nerve fiber pathology in type 2 diabetes. MATERIALS AND METHODS Sudomotor function was quantified by Neuropad test, and sweat gland duct and corneal nerve fibers were visualized by confocal microscopy in 78 patients with type 2 diabetes stratified by diabetic neuropathy and 28 control participants. RESULTS In patients with diabetic neuropathy, sudomotor function, as judged by the time required for complete color change of a Neuropad, was impaired compared with that of controls (P < 0.0001), thereby showing deterioration was related to the severity of diabetic neuropathy (P < 0.0001). Sweat gland ducts were smaller in patients without neuropathy than in controls (P < 0.0001), and further shrinking was seen in patients with severe diabetic neuropathy (P < 0.05). Patients without diabetic neuropathy showed reduced density and length (P < 0.001) of corneal nerve fibers and beading frequency (P < 0.0001), and increased tortuosity (P < 0.0001) compared with controls, and these changes deteriorated in patients with severe diabetic neuropathy. Sudomotor function was negatively associated with corneal nerve fibers (P < 0.002) and branches (P < 0.01), and influenced by the severity of diabetic neuropathy (P < 0.0001); sweat gland duct size correlated with serum triglycerides (P < 0.02), uric acid (P < 0.01), corneal nerve branch (P < 0.03), sudomotor function (P < 0.03) and severity of neuropathy (P < 0.03). CONCLUSIONS Type 2 diabetic patients had sudomotor dysfunction and smaller sweat gland ducts compared with controls. The stage of diabetic neuropathy and corneal nerve fiber pathology were independent predictors of sudomotor dysfunction, and serum triglycerides, uric acid, corneal nerve branch, stage of diabetic neuropathy and sudomotor function were predictors of sweat gland duct size.