A 58-year-old woman presents to the emergency department with progressive fatigue and weakness for the past 6 months. She is short of breath after walking several blocks. On review of systems, she mentions mild diarrhea. She has noted intermittent numbness and tingling of her lower extremities and a loss of balance while walking. She denies other neurologic or cardiac symptoms and has no history of black or bloody stools or other blood loss. On physical examination, she is tachycardic to 110 bpm; other vital signs are within normal limits. The head-and-neck examination is notable for pale conjunctivas and a beefy red tongue with loss of papillae. Cardiac examination shows a rapid, regular rhythm with a grade 2/6 systolic murmur at the left sternal border. Neurologic examination reveals decreased sensation to light touch and vibration in the lower extremities; no depression noted. The hematology consultant on call is asked to see this patient because of a low hematocrit level. Megaloblastic anemia is suspected. Which of the following vitamin deficienciesisthe probable cause of this presentation? Discuss each option and note which deficiency isthe most likely. ● Iron ● B6 ● B12 Discuss how this vitamin deficiency impairs purine or pyrimidine metabolism. List potential laboratory tests and findingsthat would assist in your differential.

A 58-year-old woman presents to the emergency department with progressive fatigue
and weakness for the past 6 months. She is short of breath after walking several blocks.
On review of systems, she mentions mild diarrhea. She has noted intermittent numbness
and tingling of her lower extremities and a loss of balance while walking. She denies other
neurologic or cardiac symptoms and has no history of black or bloody stools or other
blood loss. On physical examination, she is tachycardic to 110 bpm; other vital signs are
within normal limits. The head-and-neck examination is notable for pale conjunctivas and
a beefy red tongue with loss of papillae. Cardiac examination shows a rapid, regular
rhythm with a grade 2/6 systolic murmur at the left sternal border. Neurologic
examination reveals decreased sensation to light touch and vibration in the lower
extremities; no depression noted. The hematology consultant on call is asked to see this
patient because of a low hematocrit level. Megaloblastic anemia is suspected.
Which of the following vitamin deficienciesisthe probable cause of this presentation? Discuss
each option and note which deficiency isthe most likely.
● Iron
● B6
● B12

Discuss how this vitamin deficiency impairs purine or pyrimidine metabolism.

List potential laboratory tests and findingsthat would assist in your differential.