Diabetic peripheral neuropathy (DPN) is a common and serious complication of diabetes that causes numbness, pain, and weakness, often starting in the feet. Currently, there is no cure, and early diagnosis is difficult with standard tests alone. This observational study aims to find better ways to detect DPN in its early stages.

The researchers will use high-frequency ultrasound, a painless and non-invasive imaging tool, to measure two things in patients with type 2 diabetes: the cross-sectional area of the sciatic nerve (to look for swelling) and the blood flow velocity in the inferior gluteal artery (a vessel that supplies the nerve).In parallel, a bioinformatics analysis has identified a key target gene, Matrix Metalloproteinase 9(MMP9), which may play a role in nerve damage through a specific signaling pathway. The level of this protein will be measured in the patients' blood.

A total of 120 participants will be grouped by the severity of their nerve damage, assessed by Toronto Clinical Scoring System (TCSS). The study will investigate whether the ultrasound measurements correlate with the clinical scores, nerve conduction studies, and the blood levels of the target protein. The ultimate goal is to combine these ultrasound structure, blood flow function, and molecular markers to build a more accurate tool for the early diagnosis and precise management of DPN, bridging the gap from early warning to mechanism-based care.

This study is a prospective, observational, cross-sectional investigation designed to explore the early diagnostic value of high-frequency ultrasound in patients with type 2 diabetic peripheral neuropathy(DPN) by integrating bioinformatics-derived molecular markers. The study aims to validate a "Structure-function-molecule" cascade hypothesis for DPN progression.

Background and Rationale:

DPN is a highly disabling complication of diabetes with no current disease-modifying treatment, underscoring the urgent need for early detection. Prior work by our group found that elevated N/OFQ in DPN rats was associated with reduced limb blood flow, mediated by Membrane Metallo-Endopeptidase(MME). Shifting the focus from vascular to neural mechanisms, the present study employed independent bioinformatics analysis and identified MMP9 as a core target gene linking N/OFQ to DPN-related nerve damage, enriched in the AMPK signaling pathway. This clinical study therefore aims to validate MMP9 as a serum biomarker and examine its correlation with sciatic nerve cross-sectional area and inferior gluteal artery blood flow velocity on ultrasound across DPN severity grades.

Study Design and Participants:

A total of 120 adult patients with type 2 diabetes mellitus, diagnosed according to World Health Organization criteria, will be consecutively recruited from the Endocrinology Department of the Second Hospital of Shanxi Medical University.

Grouping and Assessments:

Participants will be stratified into three distinct severity grades based on the Toronto Clinical Scoring System(TCSS): Grade 1 (0-5 points), Grade 2 (6-9 points), Grade 3 (≥10 points). Each participant will undergo the following integrated assessments:

1. Demographic and Clinical Data Collection: Records include age, sex, body mass index, diabetes duration, HbA1c, and lipid profile.
2. Ultrasound Examination: With the patient in a lateral decubitus position (hip and knee flexed), a high-frequency linear probe will be placed at the midpoint between the ischial tuberosity and the greater trochanter to visualize the sciatic nerve. Color and pulsed-wave Doppler will subsequently measure blood flow velocity in the inferior gluteal artery.
3. Serum Biomarker Detection: Venous blood samples will be collected and centrifuged. Serum levels of the target protein MMP9 will be quantified.
4. Nerve Conduction Studies:

Standard electrophysiological parameters, including motor nerve conduction velocity(MNCV) and sensory nerve conduction velocity(SNCV) for the lower limbs, will be recorded for correlation.

Outcome Measures and Statistical Analysis:

Statistical analysis will employ ANOVA or Kruskal-Wallis tests for inter-group comparisons. Pearson or Spearman correlation coefficients will quantify the relationships among nerve structure, blood flow, and molecular markers. The combined diagnostic performance will be assessed using receiver operating characteristic (ROC) curves and logistic regression models to calculate the area under the curve (AUC). The study hypothesizes that a multimodal diagnostic model integrating imaging and serum biomarkers will provide superior sensitivity and specificity for early DPN detection compared to single-modality assessments alone.

Inclusion Criteria:

• Patients diagnosed with type 2 diabetes mellitus according to the World Health Organization (WHO) diagnostic criteria; Aged between 20 and 75 years; Willing to provide written informed consent; Ability to comply with all study assessments including ultrasound examination, nerve conduction studies, and blood sampling.

Exclusion Criteria:

• Peripheral neuropathy caused by non-diabetic conditions, including severe hepatic or renal disease, nutritional deficiencies, connective tissue diseases, or other metabolic or hereditary disorders; Nerve root compression due to cervical spondylosis or lumbar disc herniation; History of chronic alcohol abuse or long-term exposure to toxic substances (e.g., heavy metals) that may cause peripheral nerve damage; History of medication use known to affect peripheral nerve function (e.g., isoniazid, furazolidone)

This study will recruit 120 adult male and female patients diagnosed with type 2 diabetes mellitus from the Endocrinology Department of the Second Hospital of Shanxi Medical University. All participants will be stratified into groups based on diabetic peripheral neuropathy (DPN) severity assessed by the Toronto Clinical Scoring System (TCSS). Participants will include patients across the full spectrum of DPN severity, ranging from those with no or minimal neuropathy signs to those with severe clinically evident neuropathy. The study does not include a healthy non-diabetic control group. Participants will undergo a single-visit assessment including high-frequency ultrasound of the sciatic nerve and inferior gluteal artery, nerve conduction studies, and blood sample collection for serum biomarker analysis.

This is a single-center, investigator-initiated observational study conducted as part of a postgraduate thesis. Individual participant data will not be shared due to institutional data privacy regulations and the absence of a dedicated data-sharing infrastructure. Requests for summary-level results may be considered upon reasonable inquiry to the principal investigator.