Metformin-Induced B12 Deficiency

A 66-year-old woman presents with a 6-month history of progressively worsening fatigue and new peripheral numbness. She reports sleeping well (~8 hours/night) but has reduced daytime energy and gets worn out more easily. She denies shortness of breath, edema, or chest pain, and can lie flat while sleeping with 1–2 pillows; she remains able to climb stairs multiple times daily in her two-story home. Over the same period, she has developed increasing numbness of her hands and feet described as “falling asleep,” sometimes with a burning sensation, without any associated trauma or thermal injury.