Role of inflammation in sensory neuropathy in prediabetes or diabetes

Objectives - Prediabetes includes individuals with impaired glucose metabolism, and it has been associated with various complications of diabetes mellitus (DM), including peripheral neuropathy. We aimed to investigate the associations between pro-inflammatory (TNF-alpha) and anti-inflammatory (IL-10) cytokines and neuropathy of very distal sensory nerves in patients with prediabetes or type 2 DM. Materials and Methods - We included 50 patients with prediabetes, 50 patients with type 2 DM, and 44 controls in the study. Plasma levels of HbA1c, TNF-alpha, and IL-10 were analyzed. Electrodiagnostic testing was performed on dorsal sural and medial plantar sensory nerves, which are the very distal sensory nerves of the feet. Results - Abnormalities in nerve conduction studies (NCS) of the dorsal sural and medial plantar sensory nerves were substantially higher in patients with prediabetes or type 2 DM. In addition, plasma levels of TNF-alpha were significantly higher in patients with type 2 DM than in controls, whereas IL-10 levels were significantly lower in patients with both prediabetes and diabetes. However, we found no correlation between the levels of HbA1c, TNF-alpha, IL-10, and abnormalities in NCS of the dorsal sural or medial plantar sensory nerves in either patient group. Conclusions - To our knowledge, this is the first study to assess the relationships between TNF-alpha, IL-10, and NCS of the most distal sensory nerves in patients with prediabetes or type 2 DM. The mechanisms involved in the pathogenesis of DM and diabetic peripheral neuropathy are complex. The pro-inflammatory stage and the high incidence of neuropathy in patients with prediabetes may suggest a possible causative effect; however, the potential role of inflammation in the pathogenesis of peripheral neuropathy needs further clarification.