P16 - Lean mass as a key determinant of bone density in primary hyperparathyroidism: insights from dual-energy x-ray absorptiometry (DXA)-derived body composition analysis

Background/Introduction Primary hyperparathyroidism (PHPT) is known to have a substantial impact on bone mineral density (BMD), yet the influence of body composition remains unclear. Purpose This study aimed to explore associations between Dual-energy X-ray Absorptiometry (DXA)-derived lean and fat mass parameters and BMD at key skeletal sites in patients with PHPT. Methods We conducted an analysis of BMD at the lumbar spine, hip, and distal radius (forearm), alongside body composition indices, in a cohort of 60 adults diagnosed with PHPT. All patients were evaluated prior to any treatment. Univariate and multivariable linear regression models were employed to assess the relationships between BMD and body composition parameters, including appendicular lean mass index (AP_LMI), fat mass index (FMI), muscle mass index (MMI), total fat mass, and fat mass percentage (FM%). Results The mean BMD values of the cohort were: lumbar spine 0.938 ± 0.15 g/cm2, total hip 0.760 ± 0.14 g/cm2, femoral neck 0.662 ± 0.13 g/cm2, and forearm 0.476 ± 0.08 g/cm2. Body composition analysis showed a mean AP_LMI of 6.58 ± 1.22 kg/m2, FMI of 13.33 ± 4.48 kg/m2, MMI of 15.97 ± 2,47 kg/m2, total fat mass of 34.19 ± 11.47kg, and fat mass percentage (FM%) of 43.6 ± 7.1%. In univariate analyses, AP_LMI (p = 0.009), FMI (p = 0.019), MMI (p = 0.027), and total fat mass (p = 0.003) demonstrated significant associations with total hip BMD. In multivariable analysis, AP_LMI remained a borderline significant predictor of total hip BMD (β = 0.294, p = 0.067). For forearm BMD, univariate analysis showed significant associations with AP_LMI (p = 0.021) and FM% (p = 0.011). In the multivariable model, AP_LMI remained an independent predictor (p = 0.009), while FMI showed a borderline inverse association (p = 0.068). No significant associations were observed between body composition parameters and lumbar spine BMD. Conclusion(s) In individuals with PHPT, lean mass emerges as an independent predictor of BMD. This highlights the importance of muscle mass, advocating for the incorporation of lean mass assessment in DXA-based evaluations for PHPT and the value of interventions aimed at increasing lean mass in this population.