[Post-transplantation osteoporosis]

In the last two decades organ transplantation has become an effective and established therapy for end-stage disease of various organs. The increase in survival has been due to the greater immunosuppressive capacity of regimens that include cyclosporin. During the first few months after transplantation cyclosporin is associated with high-dose steroids, which produce deleterious effects on bone and mineral metabolism. These effects are superimposed on the previous bone lesions produced by the underlying chronic diseases. Rapid bone loss occurs specially during the first 6 to 12 months after transplantation, when the incidence of fractures is greater. The majority of the fractures involve the spine. Fracture rates are lower after renal transplantation (7 to 11% in nondiabetic renal transplant recipients) and higher in the recipients of other organ transplants: 17.2 to 42% after liver transplantation, 18 to 50% after cardiac transplantation and 25 to 29% after lung transplantation. No pretransplant densitometric or biochemical parameter can adequately predict fracture risk in the individual patient. Despite this, patients with low bone mineral density at the hip, particularly in women, tend to have an increased risk of fracture. Patients can have vertebral fractures despite normal bone mineral density at the spine. Pathogenesis of bone loss is multifactorial. Patients with renal and liver diseases have either renal or hepatic osteodystrophy prior to transplantation that predispose to bone loss, and many patients awaiting pulmonary transplantation already have osteoporosis due to the use of corticosteroids for their lung disease. Rapid bone loss after transplantation depends, as suggested by prospective biochemical parameters, on a decrease in bone formation (reduction in osteocalcin levels) and an increase in bone resorption. Steroids seem to be the principal determinants of these derangements, although some role of cyclosporin cannot be excluded. Other factors that contribute to bone loss are secondary hyperparathyroidism and hypogonadism. Calcium supplementation and vitamin D administration as the only preventive measures do not seem to reduce fracture risk. The most promising regimens to prevent bone loss after transplantation seem to be the use of bisphosphonates immediately prior to and during the first year after transplantation.