Analysis of three-dimensional bone mineral density and bone strength measured by quantitative computed tomography following denosumab discontinuation in a patient with postmenopausal osteoporosis

Koki Tsuchiya,¹ Koji Ishikawa,¹ Soji Tani,¹ Yusuke Oshita,² Takuma Kuroda,¹ Ryo Yamamura,¹ Haruka Emori,¹ Hiroshi Maruyama,¹ Akira Matsuoka,¹ Yoshifumi Kudo,¹ Toshiyuki Shirahata,¹ Tomoaki Toyone,¹ Takashi Nagai,¹ Katsunori Inagaki<sup>1

1</sup>Department of Orthopaedic Surgery, Showa University School of Medicine, Tokyo 142-8666, Japan; ²Department of Orthopaedic Surgery, Yamanashi Red Cross Hospital, Yamanashi, Japan

Abstract: Discontinuation of denosumab during osteoporosis treatment leads to rapid loss of bone mineral density and induces a bone turnover rebound effect. Previous studies have reported analysis based on dual-energy X-ray absorptiometry scanning (DXA). Here, we report the first case involving analysis of three-dimensional bone mineral density and bone strength, measured by quantitative computed tomography (QCT) after discontinuation of denosumab. An 82-year-old woman who discontinued denosumab because of patient’s wish was administered the fifth dose after a gap of 14 months. Her bone mineral density evaluated by DXA and QCT, bone strength, and bone turnover marker levels showed significant rebound phenomenon. The levels of the cortical parameters of the hip were also decreased indicating an increased risk of femoral fractures after denosumab interruption. Our case highlights the increased risk of fractures after discontinuation of denosumab. Therefore, denosumab must be used judiciously without interruption in the dosage schedule.

Keywords: lumbar spine, femoral neck, bone turnover markers, cortical bone, biomechanical analysis