Journal of Obesity summary on Metabolic Bone Disease article

Feb 11, 2011

I found an article on Metabolic Bone Disease from the Journal of Obesity. I am including the summary and highlighting the areas that I think are most important. If you want to read the complete article, click this link.

Bariatric surgery has proven to be an effective and life-saving measure that provides sustainable weight loss but it is not without risk of complications, to include metabolic bone disease (MBD).

There is a causal, multifactorial relationship between bariatric surgery and MBD and for that reason MBD remains an ever-present risk in bariatric surgery patients.  Patients presenting for bariatric surgery should be evaluated for MBD and receive appropriate presurgical interventions. Postsurgically, the importance of consuming adequate protein and the correct combination of vitamins and minerals cannot be overstated, remembering that no bariatric surgical procedure is risk-free when it comes to the development of metabolic bone disease.

As clinicians, we cannot assume that our morbidly obese patients are well nourished or that they have normal bone quality.  Dual-energy X-ray absorptiometry can be used to help assess bone status in the morbidly obese, however if the DXA table limitations prevent imaging the hips and spine, the nondominant forearm is a validated option for quantifying bone mineral density.  

Not all abnormal DXA results represent primary osteoporosis and in fact, in the bariatric population, secondary bone disease is the norm and when the diagnosis has been confirmed, treating the underlying cause of the secondary disease must take precedent.  DXA Z-scores, if abnormally low, suggest the presence of secondary MBD, however it is important to remember that secondary disease can be present even in the presence of normal scores.  Clues such as proximal weakness, a history of renal oxalate stones, chronic steatorrhea, and undersupplementation should serve to alert the clinician to the possible presence of metabolic bone disease.

In addition to the AACE/TOS/ASMBS guidelines, a baseline and one year postoperative DXAs are recommended. The use of calcium citrate and cholecalciferol (vitamin D3) are the recommended forms of these supplements, and in order to achieve and maintain normal serum levels, very high doses are often required in the bariatric postoperative patient.

Caution is advised when considering the use of certain medications to treat common problems in this patient population.  Cholestyramine or other bile acid sequestrants used to control diarrhea in this patient population increase the risk of exacerbating vitamin D malabsorption and osteomalacia, and may increase the risk of bowel obstruction. The use of bisphosphonates for presumed osteoporosis carries the risk of life-threatening hypocalcemia; efficacy has not been well established in this population, and the risk for ulceration from oral preparations at the surgical anastamosis has yet to be delineated.

Finally, there is emerging evidence that bariatric osteomalacia is a unique and increasingly common phenomenon in bariatric surgery patients that can have a subtle clinical presentation but potentially devastating consequences if left unrecognized.  Investigations into the underlying mechanism of the disease, the response to aggressive repletion, and effective preventive strategies are ongoing.  The treatment regimen at this point in time includes the use of cholecalciferol and calcium citrate with frequent monitoring and dose adjustments to attain and maintain normal lab parameters.

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