question: Q:A 63-year-old woman comes to the physician for a follow-up examination. She has had numbness and burning sensation in her feet for 4 months. The pain is worse at rest and while sleeping. She has hypercholesterolemia and type 2 diabetes mellitus. Current medications include insulin, metformin, and atorvastatin. She has smoked one pack of cigarettes daily for 33 years. Her temperature is 37°C (98.6°F), pulse is 88/min, and blood pressure is 124/88 mm Hg. Examination shows full muscle strength and normal muscle tone in all extremities. Sensation to pinprick, light touch, and vibration is decreased over the soles of both feet. Ankle jerk is 1+ bilaterally. Biceps and triceps reflexes are 2+ bilaterally. Babinski sign is negative bilaterally. Laboratory studies show:
  Hemoglobin 11.2 g/dL
  Mean corpuscular volume 93 μm3
  Hemoglobin A1C 8.2 %
  Serum
  Glucose 188 mg/dL
  Which of the following is the most appropriate next step in management?"? 
  {'A': 'Ankle-brachial index', 'B': 'MRI with contrast of the spine', 'C': 'Nerve conduction studies', 'D': 'Vitamin B12 therapy', 'E': 'Venlafaxine therapy'},