OSTEOPOROSIS AFTER ORGAN-TRANSPLANTATION

Within the past 2 decades, organ transplantation has become establishe d as effective therapy for endstage renal, hepatic, cardiac, and pulmo nary disease. Regimens to prevent rejection after transplantation comm only include high-dose glucocorticoids and calcineurin-calmodulin phos phatase inhibitors (the cyclosporines and tacrolimus), which are detri mental to bone and mineral homeostasis, and are associated with rapid bone loss that is often superimposed upon an already compromised skele ton. The incidence of fracture ranges from 8% to 65% during the first year after transplantation. In general, fracture rates are lowest in r enal transplant recipients and highest in patients who receive a liver transplant for primary biliary cirrhosis. Rates of bone loss and frac ture are greatest during the first 6 to 12 months after transplantatio n. Postmenopausal women and hypogonadal men appear to be at increased risk. Although no pretransplant densitometric or biochemical parameter has yet been identified that adequately predicts fracture risk in the individual patient, low pretransplant bone mineral density does tend to increase the risk of fracture, particularly in women. However, pati ents may sustain fractures despite normal pretransplant bone mineral d ensity. Although the pathogenesis of the rapid bone loss is multifacto rial, prospective biochemical data suggest that uncoupling of bone for mation from resorption may be in part responsible, at least during the first 3 to 6 months. Prevention of transplantation osteoporosis shoul d begin well before transplantation. Patients awaiting transplantation should be evaluated with spine radiographs, bone densitometry, thyroi d function tests, serum calcium, vitamin D, parathyroid hormone, and t estosterone (in men). Therapy for osteoporosis, low bone mass, and pot entially reversible biochemical causes of bone loss should be institut ed during the waiting period before transplantation. In patients with normal pretransplant bone density, therapy to prevent early posttransp lant bone loss should be instituted immediately following transplantat ion. Most pharmacologic agents available for therapy of osteoporosis h ave not been subject to prospective controlled studies in organ transp lant recipients. However, antiresorptive drugs, such as biphosphonates , appear to hold therapeutic promise. (C) 1998 by Excerpta Medica, Inc .