Year 3common
A 45-year-old woman presents with progressive tingling in her feet, difficulty walking, and imbalance for the past three months. She also reports generalized fatigue and poor concentration. She has followed a strict vegan diet for the past 10 years. On examination, she has decreased vibration and proprioception sensation in both legs with a positive Romberg sign. Laboratory tests reveal a hemoglobin level of 10.2 g/dL and an MCV of 110 fL.
What is the most likely diagnosis?