Mechanisms of osteoporosis after hematopoietic cell transplantation

Osteopenia and osteoporosis are common complications of bone marrow and peripheral blood stem cell transplantation. Bone loss occurs in 50% to 60% of patients treated with the most common preparatory regimens. The major causes of transplant-related bone loss are primary hypogonadism (low estrogen and testosterone), secondary hyperparathyroidism due to low serum calcium, and posttransplant steroid therapy. Other transplant-related treatments that induce bone loss are discussed. Trabecular bone is particularly vulnerable to transplant-related therapies. The spine and hip contain 50% to 75% trabecular bone and are most at risk for fracture after hematopoietic cell transplantation (HCT). The structure of bone and the bone cells that are involved in maintaining skeletal integrity are discussed, followed by a discussion of the transplant-related therapies that have been shown to cause damage to bone and lead to bone loss. Recommendations for patients undergoing HCT include (1) evaluation of bone mineral density either shortly before or shortly after transplantation and appropriate intervention and monitoring based on the results; and (2) evaluation of estrogen and testosterone levels after HCT and replacement when appropriate; and (3) administration of bisphosphonate therapy to all patients on steroids for >2 months. Early intervention and prevention of bone loss can have a tremendous clinical impact for patients undergoing HCT because once significant bone loss has occurred, it is difficult to reverse.