Serum Neurofilament Light Chain Levels and Neuropathy Severity in Diabetic Polyneuropathy

Inclusion Criteria: Inclusion Criteria Age between 30 and 75 years Diagnosis of Type 2 Diabetes Mellitus for at least 1 year Ability to understand and complete clinical assessments and questionnaires Willingness to participate and provide written informed consent For the DPN+ group: Presence of diabetic polyneuropathy confirmed by clinical examination, Michigan Neuropathy Screening Instrument (MNSI), and nerve conduction studies For the DPN- group: Type 2 diabetes mellitus without clinical or electrophysiological evidence of diabetic polyneuropathy Exclusion Criteria: * Neuropathy due to causes other than diabetes (e.g., vitamin B12 deficiency, hypothyroidism, alcohol abuse, chemotherapy) Renal dysfunction (eGFR \< 60 mL/min/1.73 m²) Active infection or malignancy Inflammatory or autoimmune neurological diseases Central nervous system disorders (e.g., stroke, multiple sclerosis) Lumbar radiculopathy or peripheral entrapment neuropathy Severe visual impairment or balance disorders affecting testing Pregnancy Cognitive impairment preventing completion of questionnaires Patients with isolated small fiber neuropathy without electrophysiological evidence of large fiber involvement