MRCP2-2685
A 35-year-old woman with a history of chronic alcohol abuse, type 2 diabetes, and latent tuberculosis presents to the Emergency Department with complaints of tingling in her feet for the past four weeks. She has been taking Metformin and Isoniazid monotherapy for two months. On examination, she appears unkempt and smells strongly of alcohol. Neurological examination reveals absent ankle reflexes and diminished sensation in her lower limbs. The remainder of her examination is normal.
Investigations reveal normal fasting plasma glucose and HbA1C levels, but low serum B12 and folate levels. Her hemoglobin, white cell count, platelets, serum sodium, serum potassium, serum urea, and serum creatinine levels are within normal limits.
What is the most likely cause of her neurological symptoms?