Audit of DXA scans during bisphosphonate therapy in patients with osteogenesis imperfecta at Chris Hani Baragwanath Academic Hospital

Abstract

Introduction: DXA scan measurements and changes, pre and post bisphosphonate (BP) therapy have not been conducted at Chris Hani Baragwanath Academic hospital (CHBAH) or other centres in South Africa that are treating Osteogenesis Imperfecta (OI) patients. There are a few studies that have confirmed an increase in bone mineral content (BMC) in OI children treated with BPs. However, none of these studies have a predominantly black population which was novel to this study. Objectives: The aim of this study was to evaluate and assess the change in bone mineral density in OI children treated with BPs at CHBAH, South Africa. Methods: Medical files of 104 OI patients who were seen at the Metabolic Bone clinic from 01 January 2006 till 31 December 2015 were reviewed. DXA measurements were available on 33 patients that received BPs from baseline and during therapy at three time points (9-18 months, 18-30 months and >30 months). Three methods using white male and female reference values for calculating bone mineral content (BMC) and bone mineral density (BMD) Z- scores on whole body less head (WBLH) and lumbar spine (LS) were applied and analysed as follows: 1. Calculated Z-scores using the Zemel equation and 2. Height adjusted Z-scores for >5 year old children only and 3. DXA machine calculated Z-scores. Results: WBLH BMC and BMD Z-scores and LS BMC and BMD Z-scores showed significant increases over 30 months of treatment (p<0.01). The mean BMC and BMD Zscores (WBLH and LS) at baseline were < -2 confirming low bone mass. Mean calculated Zscores after 30 months had reached a Z-score > -2; mean height adjusted Z-scores reached a Z-score > -2 from 9-18 months onwards and mean DXA machine calculated Z-scores reached a mean Z-score > -2 after 18 months. At baseline, 83% of patients had a LS BMD height adjusted Z-score < -2 and after 30 months of BPs treatment, none of the patients had a LS BMD height adjusted Z-score < -2 (p<0.001). The mean fracture rate at baseline prior to BP therapy was 16.44 per patient year (95% CI: -1.98-34.85) and significantly decreased to 0.62 (0.27-0.97) at 9-18 months and to 1.1 (0.49-1.65) at >30 months (p<0.001) during BP therapy. Conclusion: Bisphosphonate therapy significantly increased height adjusted LS BMD Zscores to >-2 and decreased the number of fractures after 9-18 months of BP treatment in South African OI patients thus supporting the use of BPs in OI patients to minimise hospitalisation and treatment costs related to fractures.