A 53-year-old woman comes to the physician complaining of lower-extremity numbness over the last several months. Her numbness is worse at night and causes her to stumble a lot, but she has not had any major falls. She has become more irritable and may have had some memory loss recently. The patient has no muscle weakness, language difficulties, or vision problems. Her bowel movements are predominantly loose. Her medical problems include a roux-en-Y gastric bypass surgery 3 years ago, hypertension, chronic back pain, and diet-controlled diabetes mellitus after successful weight loss. The patient's medications include lisinopril, amlodipine, chlorthalidone, and a multivitamin. She works as an administrative assistant and has no work-related problems.
Her vital signs are within normal limits. Body mass index is 29 kg/m². Examination shows decreased sensation to light touch in her feet and lower legs. She also has loss of vibration and proprioception in her feet bilaterally. Strength, tone, and bulk are within normal limits. Gait is narrow based and steady. The remainder of the examination is within normal limits.
Which of the following is the most likely cause of her symptoms?

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11ec193a_9811_9786_853d_9ba9c5f28411_MD0002_00 Roux-en-Y gastric bypass (RYGB) does not usually affect macronutrient absorption but can affect micronutrient absorption, as shown in the Table. RYGB patients have increased risk for deficiency of calcium, iron, vitamin B12, fat-soluble vitamins (A, D, E, and K), thiamine, and folate. Inadequate calcium and vitamin D intake, combined with the decreased absorption, can lead to secondary hyperparathyroidism, osteopenia, and metabolic bone disease. With RYGB, the majority of the stomach is bypassed, leading to possible vitamin B12 deficiency as the ingested vitamin does not pass through this intrinsic factor-producing setting. Patients commonly present with cognitive deficits and peripheral neuropathy, as seen in this patient. Daily oral B12 supplementation may help reverse the neuropathy. Intravenous or intramuscular B12 may be required in patients who do not improve on oral B12. Monitoring of serum B12 and other micronutrients should be done at 3 months, 6 months, and annually after RYGB. (Choice A) Diabetic neuropathy is unlikely to cause memory problems. (Choice B) Drug-induced peripheral neuropathy is common with chemotherapy drugs, amiodarone, and other medications. This patient is not taking any medications that commonly cause peripheral neuropathy. (Choice C) Vitamin A deficiency has been associated with night/complete blindness, poor bone growth, dermatologic issues, and immune deficiencies, which are not seen in this patient. (Choice E) Zinc deficiency may present with abdominal pain, anorexia, depression, compromised wound healing, and immune dysfunction. Educational objective: About 40% of patients develop vitamin B12 deficiency after gastric bypass surgery. The resulting peripheral neuropathy from chronic vitamin B12 deficiency may not be reversible. Patients therefore should be maintained on a daily multivitamin and additional supplementation such as vitamin B12 to avoid potential complications. Monitoring of serum B12 and other micronutrients should be done at 3 months, 6 months, and annually after Roux-en-Y gastric bypass. __________ References: Micronutrient deficiencies after bariatric surgery. (http://www.ncbi.nlm.nih.gov/pubmed/20363593) Nutritional consequences of weight-loss surgery. (http://www.ncbi.nlm.nih.gov/pubmed/17509392) Comparison of nutritional consequences of conventional therapy of obesity, adjustable gastric banding, and gastric bypass. (http://www.ncbi.nlm.nih.gov/pubmed/16901358)

A 53-Year-Old Woman Comes to the Physician Complaining of Lower-Extremity