[Early diagnosis of diabetic autonomic neuropathy by corneal confocal microscopy]

To investigate the early diagnostic value of corneal confocal microscopy by observing corneal innervation alteration in patients with autonomic neuropathy with impaired glucose tolerance.

A total of 50 subjects with neuropathy with impaired glucose tolerance or newly diagnosed type 2 diabetes, including 20 subjects with diabetic autonomic neuropathy (AN) and 30 subjects with non-autonomic neuropathy (NAN) according to the result of cardiovascular autonomic function test, and 50 aged-matched control subjects were included in this study. All the subjects came from the Department of Neurology and Endocrine from Jan to Aug 2014, and underwent a detailed evaluation of neuropathic symptoms, corneal confocal microscopy, the Survey of Autonomic Symptoms, sympathetic skin response and contact heat evoked potential test.

T test indicated patients with AN had significant reductions in nerve branch density (NBD) and nerve fiber density (NFD), and increase in corneal nerve fiber tortuosity (NFT) compared with the NAN patients (t=10.17, 4.81, 7.78; P=0.002, 0.031, 0.003). Though corneal nerve fiber length (NFL) decreased ((15±5) vs (13±5) mm/mm2), there is no statistic significance (t=1.275, P=0.232). Pearson's correlation analysis showed the severity of autonomic neuropathy significantly correlated with cornea nerves damage. The Survey of Autonomic Symptoms (SAS) significantly correlated with NFT, NFD, NFL (r=0.628, -0.304, -0.217; P<0.001, P=0.002, 0.03). NFT was the most significant determinant for the severity of autonomic neuropathy among the four observed parameters.

Corneal confocal microscopy provides a new sensitive non-invasive means to detect autonomic nerve fiber damage in patients with impaired glucose tolerance and would be of value in assessing neuropathic autonomic symptoms in clinical practice and epidemiologic studies.