Bariatric surgery: Think about osteomalacia too

Around 9% of patients with previous bariatric surgery referred for osteoporosis treatment may have osteomalacia. Increased serum total alkaline phosphatase values should alert clinicians to this diagnosis since it requires a differential treatment approach, with some patients needing high doses of calcium or even parenteral vitamin D supplementation.

The development of osteoporosis and fractures is a well-documented complication of bariatric surgery (BS). Nevertheless, subjects undergoing BS can also develop osteomalacia, which can be easily misdiagnosed as osteoporosis.

To analyze the prevalence of osteomalacia and the main clinical characteristics of subjects with previous BS referred to a Rheumatology Department for osteoporosis treatment.

This retrospective study included a cohort of 46 subjects (aged 42-77 years) with previous BS referred for osteoporosis treatment. Clinical data were obtained from a review of medical records, including the type and time since surgery, treatment with calcium and/or vitamin D, and clinical, laboratory, radiologic, and densitometric data. Osteomalacia was diagnosed by compatible bone biopsy and/or clinical criteria (two of the following: low calcium, low phosphate, elevated total alkaline phosphatase [TAP], or suggestive radiology).

Four out of 46 patients (8.7%) presented osteomalacia criteria; most were women (3/4) treated with malabsorptive surgery (from 4 to 13 years previously). All presented increased serum TAP and parathyroid hormone values, and most presented hypocalcemia and low vitamin D levels. Bone scan was compatible with osteomalacia in most subjects, and all subjects presented densitometric osteoporosis, with most developing fractures/pseudofractures after BS. No subject was referred to our department with clinical suspicion of osteomalacia.

Nearly 9% of patients 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 patients needing high doses of calcium or even parenteral vitamin D supplementation.