Follow up of bariatric surgery patients

A 62-year-old female who is five years s/p Roux-en-Y gastric bypass surgery came to see me recently for consultation regarding hyperparathyroidism. After the surgery, she lost over 170 lb. Her primary care physician astutely ordered additional testing including vitamins A, D, E, and B12.

The labs were within the normal laboratory reference ranges with the exception of the parathyroid hormone. It was elevated on two occasions: 166 pg/mL and 156 pg/mL (15 to 50 pg/mL). Her total calcium was 8.7 mg/dL (8.4 to 10.2 mg/dL) and ionized calcium was 4.79 mg/dL (4.80 to 5.70). Reportedly, the vitamin D was “normal.” The patient was sent for consultation because of the elevated PTH.

Indeed, the vitamin D was normal at 53 pg/mL (22 to 67 pg/mL); however this was 1,25 dihydroxy-vitamin D and not 25-hydroxy-vitamin D.

I ordered a 25-hydroxy-vitamin D which was 16 ng/mL (25 to 80 ng/mL). Thus, the elevated PTH is presumably due to secondary hyperparathyroidism from vitamin D deficiency and GI malabsorption. As we all know, 1,25 dihydroxy-vitamin D is not reliable in assessing dietary vitamin D status. I prescribed ergocalciferol and will be following up on this in the future.

However, this patient also described an unusual history of difficulty concentrating, disequilibrium, parathesias and unsteady gait. Previous neurology consultation and neuropsychologic testing failed to identify any explanation for her symptoms.

Because thiamine deficiency can occur in post-bariatric surgery patients, I obtained a thiamine. It was mildly low at 77 nmol/L (normal: 80 to 150 nmol/L). Thiamine levels are not frequently tested in the post-bariatric population but beriberi has been reported. In gastric bypass patients, this is most commonly “dry” beriberi with neurologic sequelae as compared to “wet” beriberi with cardiovascular involvement and edema.

I do not know if the mildly-decreased thiamine is related to her symptoms. Thiamine levels are expected to be at their lowest during the period of rapid weight loss occurring in the months immediately after the procedure. It is possible her thiamine had been much lower in the past when she was rapidly losing weight. I elected to replace thiamine and observe.

Bariatric surgery is useful in the management of the morbidly obese who have failed other therapeutic modalities. Although bariatric surgery is not without risk, it can improve many of the complications of obesity including type 2 diabetes, obstructive sleep apnea, hypertension and dyslipidemia.

However, bariatric surgery is also associated with long term complications including micronutrient deficiency. After successful weight loss, patients are discharged by the surgeon back to their primary care physicians who are often unaware of the need for long term monitoring and follow up.

A consensus statement for the peri-operative management of bariatric surgery patients was released by the American Association of Clinical Endocrinologists, The Obesity Society, and the American Society for Metabolic & Bariatric Surgery. (Endocr Pract. 2008;14(No. 3): 318-336). This is an excellent resource which I highly recommend to all involved in the care of bariatric surgery patients.