Sensory Ataxia Mimicking Diabetic Neuropathy in a Long-Term Metformin User: A Case Report From Korea

A 66-year-old man with long-standing diabetes and prolonged metformin exposure presented with a 10-year history of distal paresthesia and progressive imbalance, previously attributed to diabetic neuropathy. Bedside examination demonstrated a positive Romberg sign, impaired distal joint position sense, and reduced vibration sense, suggesting sensory ataxia with posterior column involvement. Mild macrocytosis without anemia was identified. In a resource-limited primary care setting where confirmatory testing was not immediately available, empirical methylcobalamin was initiated. The patient subsequently reported resolution of paresthesia and substantial improvement in gait stability. This case highlights the importance of reassessing presumed diabetic neuropathy when bedside findings suggest an alternative and potentially reversible diagnosis.