Response: Association between Diabetic Polyneuropathy and Chronic Complications in Type 2 Diabetic Patients (Diabetes Metab J 2011;35:390-6)

We appreciate the interest and comments on our study, "Association between diabetic polyneuropathy and cardiovascular complications in type 2 diabetic patients," which was published in Diabetes & Metabolism Journal 2011;35:390-6.

Diabetic polyneuropathy is one of the complications of chronic diabetes related to long-standing hyperglycemia and is a common cause of morbidity in diabetic patients. Diabetic polyneuropathy develops under the conditions of chronic hyperglycemia, associated with metabolic derangements and cardiovascular risk factors [1]. Recently, the close relationships between diabetic polyneuropathy and micro- or macroangiopathy have been reported [2-4]. Results from a population-based study of type 2 diabetic patients in Sweden showed that peripheral sensory neuropathy, assessed by 10 g monofilament and vibration perception threshold was associated with retinopathy and overt nephropathy [2]. In the EURODIAB Prospective Complications Study, the risk factors for cardiovascular disease including hypertension, total cholesterol, smoking, and previous cardiovascular disease increased the incidence of abnormal vibration perception threshold in type 1 diabetes mellitus [5]. Several studies have reported associations between diabetic polyneuropathy and cardiovascular mortality [6-8]. In our study, we investigated the association between diabetic polyneuropathy assessed by electrophysiological testing and chronic complications in type 2 diabetic patients. In our study, the prevalence of diabetic retinopathy, nephropathy or autonomic neuropathy was higher in patients with diabetic polyneuropathy. Diabetic polyneuropathy was associated with a high prevalence of risk factors for macrovascular complications, such as poor metabolic control, dyslipidemia, and hypertension. In multivariate analysis, diabetic polyneuropathy was independently associated with cardiovascular disease (odds ratio, 1.801; 95% confidence interval [CI], 1.009 to 3.214).

Diabetic sensorimotor polyneuropathy is a form of axonal neuropathy associated with diabetes. Among several methods for evaluating peripheral neuropathy, nerve electrophysiological tests have emerged as important tools for tracing the onset and progression of peripheral neuropathy. Recently, the Toronto Diabetic Neuropathy Expert Group proposed the use of nerve conduction testing as an early and reliable indicator of the development of polyneuropathy for epidemiologic surveys or controlled clinical trials [9]. The diagnostic sensitivity of nerve conduction studies can be improved by additional parameters such as F-wave. However, as noted by Dr. Ko et al., our study has some limitations. Although nerve electrophysiological studies are highly reproducible, sensitive and objective methods of investigating diabetic polyneuropathy and have a key role in excluding the other causes of neuropathy, they have limitations in the assessment of small-fiber dysfunction [10]. Also, there are the discomforts of the procedures and limits on the availability for routine diagnostic evaluation in clinical practice [11]. Despite these limitations, the results of our study indicate the close relationship between electrophysiologically diagnosed polyneuropathy and cardiovascular disease in type 2 diabetic patients. Further studies are necessary to determine a causal relationship or possible mechanisms between diabetic polyneuropathy and cardiovascular adverse events.