Preoperative Thoracic Muscle Mass Predicts Bone Density Change After Parathyroidectomy in Primary Hyperparathyroidism

Context: Predicting bone mineral density (BMD) gain after parathyroidectomy may influence individualized therapeutic approaches for treating patients with primary hyperparathyroidism (PHPT). Objective: This study aimed to assess whether skeletal muscle mass data could predict BMD change after parathyroidectomy in patients with PHPT. Methods: This retrospective study collected data from 2012 to 2021 at Severance Hospital, Seoul, Korea. A total of 130 patients (mean age, 64.7 years; 81.5% women) with PHPT who underwent parathyroidectomy were analyzed. Thoracic muscle volume (T6-T7 level) was estimated using noncontrast parathyroid single photon emission computed tomography/computed tomography (SPECT/CT) scans and an automated deep-learning-based software. The primary outcome assessed was the change in femoral neck BMD (FNBMD, %) 1 year after parathyroidectomy. Results: The median degree of FNBMD change after parathyroidectomy was + 2.7% (interquartile range: -0.9 to + 7.6%). Elevated preoperative PTH level was associated with lower thoracic muscle mass (adjusted β: -8.51 cm3 per one log-unit PTH increment, P = .045) after adjusting for age, sex, body mass index (BMI), and baseline FNBMD. One SD decrement in thoracic muscle mass was associated with lesser FNBMD (adjusted β: -2.35%, P = .034) gain and lumbar spine BMD gain (adjusted β: -2.51%, P = .044) post surgery after adjusting for covariates. Conclusion: Lower thoracic skeletal muscle mass was associated with elevated preoperative PTH levels in patients with PHPT. Lower skeletal muscle mass was associated with lesser BMD gain after parathyroidectomy, independent of age, sex, BMI, preoperative BMD, and PTH level.