ANSWER: D
Critique
This patient has vitamin B12 deficiency, which is common in the elderly. In addition, gastrectomy can produce cobalamin deficiency due to lack of gastrin and pepsin resulting in impaired release of dietary B12 from ingested proteins. Also, the lack of intrinsic factor will result in impaired absorption of B12. B12 and folate are required to metabolize homocysteine to methionine. Therefore, with deficiency of either folate or B12, there is an increase in serum homocysteine levels. B12 is also a cofactor in the synthesis of succinyl-CoA from methylmalonyl-CoA and therefore, with B12 deficiency, methylmalonic acid levels are also elevated. Hypoglycemia would not explain this constellation of symptoms. Microscopic colitis causes diarrhea but does not cause dementia or cognitive impairment, glossitis, or taste disturbances. The dominant micronutrient deficiencies with celiac disease are iron and calcium malabsorption, and while B12 deficiency is possible with extensive disease, it is not seen as commonly, and celiac would not be the most likely etiology for her B12 deficiency.
Reference
1. Sumner, A.E., Chin, M.M., Abrahm, J.L., et al. Elevated methylmalonic acid and total homocysteine levels show high prevalence of B12 deficiency after gastric surgery. Ann. Intern. Med. 1996;124:469.
