Case Report: Reopening the anabolic window - romosozumab added to ongoing denosumab for severe osteoporosis in two kidney transplant recipients.

Kidney transplant recipients develop disorders of mineral and bone metabolism that further impair bone strength, leading to osteoporosis and a high fracture risk. However, evidence in this setting is limited. Romosozumab, a sclerostin inhibitor with both anabolic and antiresorptive effects, is an attractive option, but its use in transplant recipients, as well as its combination with denosumab, has rarely been reported. We describe two female kidney transplant recipients with severe osteoporosis and persistently high fracture risk despite long-term denosumab, in whom romosozumab (210 mg monthly) was added to ongoing denosumab for 12 months. In both patients the bone-formation markers P1NP and BAP rose early, and bone mineral density improved preferentially at the lumbar spine (Case 1 + 5.9%, Case 2 + 11.2%), with only modest changes at the femoral neck and total hip. Serum calcium, parathyroid hormone, 25-hydroxyvitamin D and allograft function remained stable throughout, with no clinically significant hypocalcemia, and neither patient sustained a new vertebral fracture. Adding romosozumab to ongoing denosumab thus reopened the anabolic window and improved lumbar-spine bone mineral density without compromising mineral metabolism or graft function. This combination may represent a reasonable option for carefully selected transplant recipients who continue to lose bone or to fracture despite antiresorptive therapy, pending confirmation in controlled studies.