The role of pro-inflammatory and anti-inflammatory factors in the formation of polyneuropathies in patients with type 2 diabetes mellitus

Background. Over the past 5 years, researchers have reported the prevalence of peripheral polyneuropathy (PPN) to range from 6 to 51 % among patients with diabetes mellitus (DM). Among patients with type 2 DM, distal symmetric polyneuropathy represents the most common type of PPN. Clinicians need to differentiate it from other forms of PPN, particularly chronic inflammatory demyelinating polyneuropathy. In this type of lesion, local and systemic inflammatory processes, especially the interaction between pro- and anti-inflammatory cytokines (IL-6 and IL-10), play a key role. This study aimed to identify the relationship between IL-6 and IL-10 levels and the clinical features of PPN in type 2 DM. Materials and methods. We examined 96 patients diagnosed with type 2 DM complicated by PPN. All of them underwent electroneuromyographic study and, based on its results, formed three groups: 1 — axonal type of peripheral nerve damage (n = 37); 2 — demyelinating type (n = 29); 3 — mixed type (n = 30). We also measured the blood serum levels of IL-6 and IL-10. In addition, all patients completed standardized questionnaires and scales: PainDetect, MNSI, TSS, and NIS-LL. Results. The level of IL-6 in all studied groups was higher than in the control one, with all p-values < 0.05. Group 3 had the highest value (16.40 ± 2.89 pg/ml), while patients with the axonal type of PPN showed the lowest (7.44 ± 0.52 pg/ml). The IL-10 levels in group 1 closely resembled those in controls and were significantly lower than in groups 2 and 3 (both p < 0.005). Patients with axonal degeneration showed stronger correlations between IL-6 and IL-10: r = 0.77 in group 1 and r = 0.83 in group 3 (both p < 0.005). Patients in group 3 reported the most intense symptoms on the MNSI, TSS, and NIS-LL scales (18.76 ± 1.98, 12.51 ± 1.66, and 32.72 ± 3.47 points, respectively), whereas group 2 showed the lowest scores (10.04 ± 1.53, 5.14 ± 0.95, and 18.38 ± 1.48 points, respectively). Conclusions. The study found persistently elevated IL-6 and IL-10 levels in all patients with type 2 DM and identified strong direct correlations between these cytokines, particularly in groups 1 and 3. The analysis of clinical and neurological symptoms using MNSI, TSS, and NIS-LL scales revealed strong correlations between the scores and moderate to strong direct correlations with IL-6 levels across all groups and with IL-10 levels in groups 1 and 3.