This case of postgastric bypass osteomalacia, secondary hyperparathyroidism, and resulting pelvic fractures highlights important concepts in bone fragility, as well as the significance of the oft-ordered and poorly understood 25-OH vitamin D. Obesity is well-recognized to be protective against pelvic and hip fractures (1). Although gastric bypass increases the risk for potential bone loss, it is intriguing that this patient had pelvic fractures years after she regained most of her weight, suggesting mechanical unloading was unlikely a major contributor.
The Institute of Medicine recommends a 25-OH vitamin D ≥20 ng/mL as generally adequate for bone health. Post-gastric-bypass patients may require 25-OH vitamin D concentrations much higher than 20 ng/mL to permit appropriate absorption of calcium and phosphorus in the gut. Notably, most post-bypass patients who maintain 25-OH vitamin D concentrations around 30 ng/mL fail to demonstrate a prominent increase in parathyroid hormone (PTH), emphasizing the uniqueness of this case regarding PTH concentrations. Although the iron concentration was low, other nutrients' concentration, including B12 concentration, was normal, underscoring a need to maintain a high suspicion for calcium malabsorption and secondary increase of PTH in such patients.
As with many post-gastric-bypass osteomalacia cases, bone density by dual-energy x-ray absorptiometry (DXA) demonstrates osteopenia, not osteoporosis, and this, combined with patient age of <65 years, typically represents a low fracture risk. However, DXA results often fail to correlate with bone fracture risk in younger patients with secondary causes of fragility or mineralization defects. Moreover, bone loss often occurs rapidly after gastric bypass in multiple skeletal sites (2), and the rate of bone density loss may be more detrimental than the absolute value in increasing bone fragility. In addition to osteomalacia, this patient likely had osteitis fibrosa cystica or brown tumor changes on the basis of high PTH concentrations, which may have existed for a long time and are frequently associated with bone pain.
Footnotes
Author Contributions: All authors confirmed they have contributed to the intellectual content of this paper and have met the following 3 requirements: (a) significant contributions to the conception and design, acquisition of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; and (c) final approval of the published article.
Authors' Disclosures or Potential Conflicts of Interest: No authors declared any potential conflicts of interest.
- Received for publication October 5, 2017.
- Accepted for publication October 10, 2017.
- © 2017 American Association for Clinical Chemistry
