Investigation of small fiber neuropathy in patients with diabetes mellitus with corneal confocal microscopy

Objective:Diabetes Mellitus (DM) is a chronic disease with hyperglycemia due to insulin deficiency or insulin action defect. Diabetic polyneuropathy is one of the microvascular complications of diabetes. Electrophysiological findings obtained by standard electromyography have an important place in the diagnosis of diabetic polyneuropathy. However, in small fiber neuropathy, standard electrophysiologic studies are normal. Therefore, new methods that can be used in diagnosis are being investigated. Corneal confocal microscopy (CCM), is a non-invasive technique that provides the opportunity to examine the corneal cellular structure. In recent years, studies have been carried out for the detection of small fiber neuropathy. Considering this information, in our study, we aimed to examine the role of the CCM technique in detecting the presence of small fiber neuropathy in diabetic patients. Materials and Methods: The study was conducted in the neurology department of Ankara City Hospital between April 2021 and October 2021. 56 patients with DM and 18 healthy controls were enrolled in this study. Demographic data of the patients, type and duration of diabetes, duration of neuropathic pain, medications used, height and weight values, blood glucose and HbA1c levels were evaluated. The individuals included in the study were divided into three groups. Patients with diabetes and polyneuropathy according to electrophysiological diagnostic criteria were classified as Group 1, patients with diabetes and neuropathic complaints and without polyneuropathy according to electrophysiological diagnostic criteria were classified as Group 2, and healthy individuals were classified as Group 3. DN4 questionnaire, LANSS neuropathic pain scale and SCOPA-AUT were carried out to the patient group. Electromyographic examination was performed in the patient and control groups in accordance with the polyneuropathy protocol. Corneal imaging was performed with corneal confocal microscopy in the Ophthalmology Clinic of the patient and control groups. IBM SPSS Statistics 26.0 (IBM Corp. Released 2012. IBM SPSS Statistics for Windows, Version 26.0. Armonk, NY: IBM Corp.) was used for the statistic analysis of the data, and the statistical significance value was accepted as p <0.05. Results: There was no significant difference between the groups in terms of age and gender. Hypertension was detected in 41.9% of individuals in Group 1 and Group 2. Individuals in Group 2 have lower DN4 and LANSS scores than those in Group 1. When diabetic patients and healthy individuals are examined, CNFD values show a statistically significant difference (p=0.018). Diabetic individuals had lower CNFD values. When diabetic patients and healthy individuals are examined, CNFL values show a statistically significant difference (p=0.047). Diabetic individuals had lower CNFL values. The CNFD values on the basis of the three groups show statistically significant differences (p=0.047). The groups that make the difference are Group 1-Group 3 and Group 2-Group 3 (respectively p=0.018, p=0.048). Conclusion: Corneal confocal microscopy is an easily applicable, non-invasive, and highly reproducible examination. It has clinical importance in terms of providing early diagnosis and treatment opportunities for small fiber involvement. The findings obtained in our study also show that CCM can be used in patients with neuropathic complaints and who cannot be detected in favor of polyneuropathy by EMG. Both the diagnosis of small fiber neuropathy in this way and the management of complications will also be easier. Keywords: Diabetes Mellitus, diabetic neuropathy, small fiber neuropathy, electromyography, corneal confocal microscopy