Endocrine Abstracts

Introduction: Discontinuation of denosumab may rarely lead to rebound fractures, although the evidence is low, since available data have derived from case reports and post-hoc analyses.

Case presentation: A 45-year old Caucasian male was presented at the outpatient clinic in February 2016 for evaluation and management of severe osteoporosis, which had been complicated with multiple vertebral low energy fractures at the 10 ^th to 12^th thoracic vertebrae (T10-T12) and at the 1^st (L1), 2^nd (L2), 4^th (L4) and 5^th lumbar vertebrae (L5). These fractures were diagnosed in 2013 after continuous back pain following a mild injury and weight-bearing activities. Severe osteoporosis was diagnosed and the patient was initially treated with teriparatide (for 24 months) showing significant improvement in physical activity. Bone mineral density (BMD) values after teriparatide treatment were 0.861 mg/cm² (T-score: –3, Z-score: –2.5) for lumbar spine, 0.78 mg/cm² (T-score: –2.2, Z-score: –1.4) for neck and 0.783 mg/cm² (T-score –2.4. Z-score: –1.7) for total hip. Evaluation for causes of secondary osteoporosis was negative. He was also receiving calcium supplementation (1000 mg/d) and cholecalciferol 800 IU/d (25-hydroxy-vitamin D concentrations: 29 ng/ml). After three injections of denosumab (March 2017), the patient’s lumbar spinre BMD increased to 0.882 mg/cm² (T-score: –2.8, Z-score: –2.2). However, he was complaining of continuous musculoskeletal pain since denosumab injections and he omitted the fourth one. The patient attended the outpatient clinic in September 2017 complaining of a new severe back pain after mild physical activity. Spine magnetic resonance imaging (MRI) revealed a new vertebral fracture in L4 and concomitant biconcave deformation of T11 and T12. After excluding other causes of low bone mass, denosumab was re-initiated.

Conclusions: This is the first case of a male patient having sustained a new vertebral fracture, nine months after his last denosumab dose. The possibility of a rebound fracture, although low, should always be taken under consideration after denosumab discontinuation, especially in patients at high fracture risk, not previously being treated with bisphosphonates.