[Early diagnosis of diabetic polyneuropathy based on the results of corneal nerve fibers examination].

Unlabelled: Laser corneal confocal microscopy (CCM) is a method of objective visualization of thin corneal nerve fibers (CNF), the structure of which changes in patients with diabetes mellitus (DM).

Purpose: To conduct comparative analysis of the results of CNF assessment using CCM and other known neurological instrumental techniques as well as evaluate their applicability to the early diagnosis of diabetic polyneuropathy (DPN).

Material And Methods: We examined a total of 46 patients (85 eyes) with type 1 DM and either subclinical (24 patients), or clinical-stage DPN (22 patients) and 50 patients (87 eyes) with type 2 DM (subclinical DPN in 27 patients and clinical-stage DPN in 23 patients). The control group consisted of 34 healthy volunteers (68 eyes). All patients underwent standard ophthalmological examination, CCM with nerve tortuosity assessment (including calculation of coefficients of CNF orientation anisotropy, K, and symmetry, K) and interocular asymmetry, electroneuromyography (ENMG), and quantitative sensory testing (QST).

Results: Analysis of the CCM results revealed a reliable decrease in the average K values in patients with type 1 and type 2 DM compared with the control group. In the group of patients with type 1 DM and subclinical DPN, correlations were revealed between the CNF tortuosity coefficients and a number of ENMG parameters, such as the M-response amplitude of the peroneal nerve (=0.73, ≤0.02), M-response amplitude of the tibial nerve (=0.58, ≤0.01), residual latency (= -0.62, ≤0.05), and peroneal nerve conduction velocity (=0.57, ≤0.01). K values correlated with the warm sensitivity threshold (=0.6, ≤0.008). Among patients with type 2 DM and subclinical DPN, the K coefficient correlated with the peroneal nerve conduction velocity (=0.46, ≤0.02), M-response amplitude of the tibial nerve (=0.6, ≤0.04), and residual latency of the peroneal nerve (=-0.56, ≤0.05).

Conclusion: The state of thin corneal nerves correlates with functional changes in the peripheral nerves. Pathological changes in CNF in patients with DM can be detected at an early (subclinical) stage of DPN using laser CCM and a program for corneal nerve tortuosity analysis.