Peripheral neuropathy is associated with insulin resistance independent of metabolic syndrome

Background: To determine the association of insulin resistance, metabolic syndrome (MetS) with peripheral neuropathy (PN). Methods: This cross-sectional study consisted of 2035 subjects in Shanghai who were classified as with MetS and without MetS. The new International Diabetes Federation (IDF) criterion was used to define MetS. HOMA-IR was applied to evaluate insulin resistance. All subjects underwent complete foot examination. PN was assessed according to the neuropathy symptom and neuropathy disability scores. Binary logistic regression was performed to analyze the contributions of insulin resistance, features of MetS to PN. Results: (1) The percentage of PN was 4.0% in our study. Patients with MetS (47.7%) had a higher percentage of PN (5.5% vs. 2.6%, respectively, P = 0.001). With the components of MetS increased (non-MetS, three, four, five), a linear increase in the proportion of peripheral neuropathy was observed (2.6%, 4.8%, 5.6% and 7.2%; respectively, P for trend = 0.001). (2) In patients with PN, the average age of patients was significantly older than the corresponding non-PN patients. Waist circumference, fasting blood glucose, HbA1c, proportion of treatment for diabetes and hypertension were significantly higher in PN group compared with non-PN group in MetS patients. (3) The frequency of dysglycemia was the highest in PN patients both with and without MetS (96.2% and 82.1%, P = 0.084). (4) After adjusting for gender and smoking history, the PN was associated with MetS [odds ratio (OR) 2.0; 95% confidence interval (CI) 1.2, 3.2; P = 0.006], and age (OR 1.1; 95% CI 1.1, 1.1; P < 0.001). When HOMA-IR was added to this binary logistic regression, the association of PN with MetS disappeared (P = 0.110), but the PN was still associated with HOMA-IR (OR 1.2; 95% CI 1.1, 1.4, P < 0.001). Conclusions: In metabolic syndrome, insulin resistance might play an important role in the development of peripheral neuropathy.