Vitamin absorption following malabsorptive bariatric surgery

Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 55-year-old woman is evaluated during a routine examination. She underwent biliopancreatic diversion with duodenal switch 8 years ago for treatment of obesity-related complications and lost 68.0 kg (150.0 lb) in the first year following surgery. Her weight has been relatively stable for the last year. She has had chronic nonbloody diarrhea since her bariatric surgery. She also has had generalized fatigue, dry skin, dry and itchy eyes, and increased difficulty seeing road signs at night while driving. Her other medical problems are type 2 diabetes mellitus and hypertension. Her prescription medications are metformin and lisinopril, and she also takes an over-the-counter multivitamin with iron. Her last colonoscopy, performed 5 years ago, was normal.

On physical examination, blood pressure is 140/79 mm Hg and pulse rate is 63/min. BMI is 25. The examination is otherwise unremarkable.

Laboratory studies reveal a hemoglobin level of 10.5 g/dL (105 g/L) and a mean corpuscular volume of 95 fL.

Which of the following deficiencies best explains this patient’s current findings?

A. Copper
B. Iron
C. Vitamin A
D. Vitamin B12

MKSAP Answer and Critique

The correct answer is C. Vitamin A.

Vitamin A deficiency is most likely to explain this patient’s findings, and the most appropriate and important study is immediate assessment of this patient’s vitamin A status with serum retinol measurement. Her ocular symptoms are very serious manifestations of vitamin A deficiency, which may be progressive and may lead to permanent visual impairment if left untreated. Symptoms associated with vitamin A deficiency include decreased vision at night or in dim light, dry eyes, corneal and/or eyelid inflammation, and rough and/or dry skin. The absorption of the fat-soluble vitamins A, D, E, and K can be severely impaired following malabsorptive bariatric surgery, including Roux-en-Y gastric bypass (RYGB) and biliopancreatic diversion with duodenal switch. Vitamin A deficiency has been reported to occur in 11% of patients after gastric bypass despite taking a daily multivitamin. This deficiency can occur within 1 year of surgery; the reported prevalence is 10% to 50% in patients with RYGB and 61% to 69% in those with biliopancreatic diversion. Vitamin A deficiency is believed to arise from multiple factors such as fat malabsorption, decreased intake from reduced overall food consumption, and possible underlying fatty liver disease. Other micronutrient deficiencies (in addition to the previously mentioned fat-soluble vitamins A, D, E, and K) that can develop following RYGB include iron, folic acid, zinc, selenium, copper, magnesium, thiamine (vitamin B1), cobalamin (vitamin B12), vitamin C, and in rare cases, riboflavin (vitamin B2) and pyridoxine (vitamin B6).

Copper deficiency may cause muscle weakness due to myeloneuropathy, ataxia, and cognitive deficits that may be difficult to differentiate from B12 deficiency. Less common neurologic findings include bilateral visual loss. Hematologic findings in copper deficiency include microcytic anemia, which may mimic iron deficiency anemia, and leukopenia.

Although iron deficiency does occur following RYGB, this patient is on iron replacement and has a normal mean corpuscular volume. Patients with iron deficiency are likely to have hypochromic, microcytic anemia and may have brittle or deformed nails, cheilitis, pica, and restless legs syndrome. Visual symptoms are not seen with iron deficiency anemia.

Although vitamin B12 deficiency may occur following RYGB, this is unlikely given this patient’s normal mean corpuscular volume. Furthermore, a vitamin B12 deficiency could lead to peripheral neuropathy and gait disturbance but not the skin or visual disturbances seen in this patient.

Key Point

The absorption of the fat-soluble vitamins A, D, E, and K can be severely impaired following malabsorptive bariatric surgery, including Roux-en-Y gastric bypass and biliopancreatic diversion with duodenal switch.

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