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Aims/introduction: Painful diabetic peripheral neuropathy (pDPN) is associated with small nerve fiber degeneration and regeneration. This study investigated whether the presence of pDPN might influence nerve regeneration in patients with type 2 diabetes undergoing intensive glycemic control., Materials and Methods: This exploratory substudy of an open-label randomized controlled trial undertook the Douleur Neuropathique en 4 questionnaire and assessment of electrochemical skin conductance, vibration perception threshold and corneal nerve morphology using corneal confocal microscopy in participants with and without pDPN treated with exenatide and pioglitazone or basal-bolus insulin at baseline and 1-year follow up, and 18 controls at baseline only., Results: Participants with type 2 diabetes, with (n = 13) and without (n = 28) pDPN had comparable corneal nerve fiber measures, electrochemical skin conductance and vibration perception threshold at baseline, and pDPN was not associated with the severity of DPN. There was a significant glycated hemoglobin reduction (P < 0.0001) and weight gain (P < 0.005), irrespective of therapy. Participants with pDPN showed a significant increase in corneal nerve fiber density (P < 0.05), length (P < 0.0001) and branch density (P < 0.005), and a decrease in the Douleur Neuropathique en 4 score (P < 0.01), but no change in electrochemical skin conductance or vibration perception threshold. Participants without pDPN showed a significant increase in corneal nerve branch density (P < 0.01) and no change in any other neuropathy measures. A change in the severity of painful symptoms was not associated with corneal nerve regeneration and medication for pain., Conclusions: This study showed that intensive glycemic control is associated with greater corneal nerve regeneration and an improvement in the severity of pain in patients with painful diabetic neuropathy., (© 2021 The Authors. Journal of Diabetes Investigation published by Asian Association for the Study of Diabetes (AASD) and John Wiley & Sons Australia, Ltd.)

The most common and debilitating microvascular complication of diabetes is diabetic peripheral neuropathy (DPN), affecting 50-90% of people with diabetes. The major manifestations of DPN are painful (pDPN) and painless diabetic peripheral neuropathy. Painful symptoms, occur in the feet and are worse at night and whilst they alert both the patient and physician, are often misdiagnosed and mismanaged. The devastating presentation of painless neuropathy with loss of sensation is foot ulceration and Charcot foot. The explosion of diabetes, especially in the South East Asian (SEA) region will result in an increasing prevalence of both painful and painless diabetic peripheral neuropathy. PubMed, EMBASE, Medline and Google Scholar databases were searched between 1990 and 2017. This highlights the widely varying prevalence of DPN and pDPN in the World Health Organization (WHO) defined SEA countries and the dearth of published studies, especially in pDPN. We believe this will provide new direction for future research on DPN in the SEA region.