Ab1245 osteomalacia related to bariatric surgery: how frequent is it?

Background The development of osteoporosis and fractures is a well-documented complication of bariatric surgery (BS), especially with procedures associated with malabsorption. Due to the gradual increase of BS performed worldwide, several national and international societies have developed clinical guidelines for managing these patients, with special attention to osteoporosis prevention and treatment. Nevertheless, these subjects can also develop osteomalacia, which can easily be misdiagnosed as osteoporosis. It is crucial to differentiate osteoporosis and osteomalacia in BS patients since different therapeutic approaches are necessary. Objectives To analyse the prevalence of osteomalacia and the main clinical characteristics of subjects with previous BS referred to the Rheumatology Department for osteoporosis treatment. Methods This was a retrospective study of a cohort of 46 subjects (aged 42-77 years) referred to the Metabolic Bone Diseases Unit of the Rheumatology Department for evaluating osteoporosis treatment. Clinical data were obtained from an in-depth review of medical records, including the type of BS (restrictive: gastric banding, and sleeve gastrectomy, or malabsorptive surgery: Roux-en-Y gastric bypass [RYGB], biliopancreatic diversion with duodenal switch), time since surgery, previous treatment with calcium and/or vitamin D, anthropometric data, clinical, laboratory, radiologic and densitometric findings. Osteomalacia was diagnosed by compatible bone biopsy and/or by Bingham and Fitzpatrick criteria [1] (two of the following: low calcium, low phosphate, elevated total alkaline phosphatase [TAP] or suggestive radiology). Results Five of the 46 patients (10.8%) presented criteria compatible with osteomalacia, two being confirmed by bone biopsy. All subjects with osteomalacia were Caucasian and most were women (4/5) treated with malabsorptive surgery (mainly RYGB) from 4 to 23 years prior to the visit. All presented increased serum TAP values (some presenting a progressive increase 1-3 years prior to the visit). Most subjects showed low serum calcium (4/5) and vitamin D serum levels; the latter were markedly decreased in 4 individuals (with only one presenting values >20 ng/ml). Parathyroid hormone (PTH) levels were increased in all subjects. Bone scan showed a pattern compatible with osteomalacia in all evaluated subjects (4/4) and bone densitometry showed values compatible with densitometric osteoporosis in most (4/5), with four individuals developing fractures/pseudofractures after BS. Three of these subjects were poorly adherent to calcium and vitamin D supplements and in 2 cases higher doses of calcium (3 g/day) and/or parenteral vitamin D administration were necessary to achieve serum vitamin D levels >30 ng/ml and decrease serum PTH levels in the posterior follow-up. Of note, no subject was referred to the Rheumatology Department with clinical suspicion of osteomalacia. Among the remaining 41 subjects, 28 (68%) presented densitometric osteoporosis and 18 (45%) developed fractures (mainly vertebral) after BS; one subject developed primary hyperparathyroidism (treated with surgery). Again, malabsorptive surgery was the most frequent surgical procedure in these subjects. Conclusion Nearly 10% of subjects with previous BS referred for osteoporosis treatment may have osteomalacia. Increased serum TAP values should alert clinicians to this diagnosis since it requires a differential treatment approach with some of these patients needing high doses of calcium or even parenteral vitamin D supplementation. Reference [1]Bingham CT, Fitzpatrick LA. Non-invasive testing in the diagnosis of osteomalacia. Am J Med 1993; 95(5):519-23. Acknowledgements: NIL. Disclosure of Interests None Declared.