A 5-year follow-up visual evoked potentials and nerve conduction study in young adults with type 1 diabetes mellitus

Central nervous system impairment is common in diabetic patients, even in the early stages of the disease, and could be associated with peripheral neuropathy. The aims of this study were to prospectively investigate central nerve conduction in young adults with type 1 diabetes using pattern-reversal visual evoked potentials (PRVEP) and to determine how those results were related to clinical risk factors and the parameters of the peripheral nerve conduction study (NCS). A total of 36 type 1 diabetic patients (15 males) 5-24 years of age (mean 14.5 ± 4.7) underwent PRVEP and NCS annually for five years. For comparison, 39 healthy age and sex matched individuals (mean 14.8 ± 5.0) were evaluated as the control group. The P100 latencies of the PRVEP were prolonged at the study entry in the patients compared with the controls (p< 0.001). Significant correlations were not found between any of the parameters of PRVEP and the glycosylated hemoglobin levels; however, the changes in the parameters of the peripheral NCS were well correlated with metabolic control. The latencies and amplitudes of the P100 were not related to the majority of the parameters of the NCS. A prolonged PRVEP latency may be a sign of optic pathway dysfunction, which begins before apparent diabetic retinopathy. Poor glycemic control proved to be an important risk factor over the 5 years in terms of its relation to the development of peripheral neural pathway abnormalities. However, once central conduction was delayed, its changes were poorly related to diabetic control and the attributes of the peripheral nerve conduction study over the 5-year follow-up. Neurology Asia 2016; 21(4) : 367 – 374 Address correspondence to: Sang-Soo Lee, MD, Department of Neurology, Chungbuk National University College of Medicine, Chungdae-ro 1, Seowonku, Cheongju, Chungbuk 28644, South Korea. Tel: +82-43-269-6336, E-mail: pnsdoctor@gmail.com INTRODUCTION The early detection of neurological alterations is an important task in the follow-up of diabetic patients, particularly for young persons with type 1 diabetes mellitus. Nerve conduction studies (NCS) have been used for this purpose. Impairments of the central nervous system (CNS) and the peripheral nervous system are frequent complications of diabetes. Moreover, CNS impairment is common in diabetic patients, even in the early stages of the disease, and could be associated with peripheral neuropathy. Nevertheless, little attention has been directed toward the chronic effects of diabetes on the CNS. While the peripheral and autonomic nervous systems’ involvements determine a large spectrum of clinical manifestations, CNS involvement is usually clinically silent and can only be uncovered by neurophysiological investigations or psychometric tests. It is important to emphasize that despite many experimental and clinical studies, this association is still uncertain, and a screening tool is needed to confirm this association. Neurophysiological tests have proven to be objective and sensitive tools for the detection of even subclinical CNS impairments. Visual evoked potential (VEP) recordings represent a mass response of cortical and probably subcortical visual areas and are used to assess the functional integrity of the visual pathway. There are uncertainties regarding whether central conduction abnormalities are related to peripheral nerve conduction abnormalities in diabetic patients. Earlier studies revealed data about the central manifestations of diabetes, but these studies did not permit a comprehensive comparative analysis of peripheral and central nervous dysfunctions. Several studies have reported that central afferent dysfunction is associated with the most common forms of diabetic neuropathy. However, contradictory results exist. In addition to these uncertainties, Neurology Asia December 2016 368 most studies have focused on type 1 patients with longstanding diabetes or adults with type 2 diabetes mellitus. Moreover, the previous studies had cross sectional designs. The aims of this study were to prospectively evaluate central nerve conduction in young adults with type 1 diabetes using pattern-reversal VEP (PRVEP) and to investigate the relations between PRVEP changes and peripheral NCS parameters. Another aim was to establish the influences of several clinical risk factors on the function of the visual pathway.