Efficacy and Safety Study of Thioctacid Oral Tablets 600mg to Treat Chinese Diabetic Patients With Distal Symmetric Polyneuropathy

Inclusion Criteria: * Subjects must fulfil all of the following criteria to be appropriate to enter into Registry (Visit 2) 1. Provision of informed consent 2. Females and males aged from 18 to 75 (inclusive), who were definitely diagnosed with diabetes 3. HbA1C\< 10％ 4. Moderate neuropathy according to Neuropathy Disability Score (NDS) \>= 4 points. Difference in score between left and right foot is not to be higher than 2 points 5. Total Symptom Score (TSS) \> 6.5 points 6. At least one of the four symptoms of the TSS has occurred continuously over the last 3 months before screening 7. Other concomitant treatments (the drugs and their dosage) have been stable over 1 month before screening Subjects must fulfil all of the following criteria before randomization： 8. TSS \> 5 points 9. TSS range (maximum TSS - minimum TSS during Run-in Period) \< 3 points during the Run-in Period 10. Compliance in Run-in Period \> 85% Exclusion Criteria: 1. Neurologic disease other than diabetic neuropathy that may produce weakness, sensory loss, or autonomic symptoms or test abnormality 2. Peripheral vascular disease severe enough to cause intermittent claudication or ischemic ulcers 3. Patients who have been hospitalized due to glucopenia or ketoacidosis in the last 3 month 4. Present ulcers on lower limbs of any cause 5. Antioxidant therapy within the last 1 month before screening (Vitamin E\> 400IU, Vitamin C\> 200mg once daily for continuous 2 weeks) 6. Any ALA therapy within the last1 month before screening 7. Opioid analgesic therapy within the last 1 month before screening 8. History of mental, psychological or behavioral conditions rendering the patient unable to follow the protocol 9. History of malignant tumors in the past 5 years except for basal cell carcinoma 10. Any severe systematic diseases, at the investigator's discretion, which will make it undesirable for the patient to participate in the trial or which could jeopardize compliance with the trial protocol, 11. ALT or AST \> 2.5 ´ upper limit of reference range 12. Cr \> 1.8mg/dL ( \> 159µmol/L) for males or \> 1.6mg/dL ( \> 141µmol/L) for females 13. History of hypersensitive to the active ingredients or excipients of ALA 14. Participation in a clinical study or treatment with a non-approved experimental medication in the last 1 month 15. Pregnant or breast-feeding women, or women of childbearing age without appropriate contraception measures