Endocrine Abstracts

There is concern about rapid reduction in bone mineral density (BMD) and early rebound vertebral fractures following discontinuation of denosumab. Our aim was to review local experience of discontinuation of denosumab, changes in BMD and fractures in patients with osteoporosis.

Methods: A retrospective analysis was conducted for patients who discontinued denosumab between March 2011 & June 2016. Denosumab withdrawal(DW) was defined as a period >6 months from the last dose of denosumab. BMD before denosumab initiation and after DW were compared.

Results: Of 32 patients in DW group, mean age was 75.4 ±10.7 years and 91% were women. 24/32 received ≥4 doses of Denosumab (median 6(IQR: 2.8)). 81.2%(26/32) received other bone-active treatments prior to denosumab. Bisphosphonates were administered in 15.6%(5/32) after DW.

12.5%(4/32) sustained 5 fractures (2 neck of femur and 3 vertebral) after DW at a mean interval of 20.2±3.7 months. 3/4 of that group had received bisphosphonates prior to denosumab treatment and none received bisphosphonates during DW.

Mean time to DXA scan from the last dose of denosumab was 12.3±10.6 months. An increase in T-score was observed at spine and hip (26.0% (IQR: 27.4) & 12.6% (IQR: 20.05)) up-to 20 months from DW. Beyond 26 months of DW there was a reduction in T scores at both hip and spine (−288.3% & −41.3% respectively).

Conclusions: We did not observe early onset, multiple vertebral fractures following DW. The first fracture in the DW group occurred at 15 months. Our data did not show a rapid early fall in BMD but beyond 26 months of DW there was evidence of a decline in BMD. We postulate that pre-treatment with bisphosphonates may protect against rapid bone loss and rebound fractures following DW. Our current practice is to administer at-least a single dose of IV zoledronic acid prior to DW.