Bone Disease in Kidney Transplant Patients

Mineral and Bone Disease in Kidney Transplant Recipients

PURPOSE OF REVIEW

Despite metabolic improvements following kidney transplantation, transplant recipients still often suffer from complex mineral and bone disease after transplantation.

RECENT FINDINGS

The pathophysiology of post-transplant disease is unique, secondary to underlying pre-transplant mineral and bone disease, immunosuppression, and changing kidney function. Changes in modern immunosuppression regimens continue to alter the clinical picture. Modern management includes reducing cumulative steroid exposure and correcting the biochemical abnormalities in mineral metabolism. While bone mineral density screening appears to help predict fracture risk and anti-osteoporotic therapy appears to have a positive effect on bone mineral density, more data regarding specific treatment is necessary. Patients with mineral and bone disease after kidney transplantation require special care in order to properly manage and mitigate their mineral and bone disease. Recent changes in clinical management of transplant patients may also be changing the implications on patients' mineral and bone disease.

Fracture risk in kidney transplant recipients: a systematic review

BACKGROUND

Fractures in men and women after kidney transplantation are associated with morbidity (including acute and chronic pain), mortality, and high economic costs.

METHODS

We systematically reviewed cohort studies that provided estimates on incidence and risk factors for fracture in kidney transplant recipients. We abstracted data in duplicate and assessed the methodological quality of each study on a 17-point scale (17 representing the highest quality).

RESULTS

We screened 2715 articles, reviewed 81, and included 10 studies totaling 262,678 recipients (study mean, 26,268 recipients; range, 61-77,430). The average follow-up ranged from 1.7 to 5.3 years. The study quality scores ranged from 8 to 13. Fracture sites varied by study resulting in a highly variable incidence rate ranging from 3.3 to 99.6 fractures per 1000 person-years. Similarly, the 5-year cumulative incidence for fracture varied ranging from 0.85% to 27%. Common factors associated with an increased fracture risk were older age, female sex, the presence of diabetes, and receipt of dialysis before transplantation. Other less common but statistically significant risk factors were a previous history of fracture and receipt of a kidney from a deceased (vs. living) donor.

CONCLUSIONS

There is poor consensus on the incidence and risk factors for fractures in kidney transplant recipients. Previous studies vary substantially in quality, fracture definitions, and the characteristics of recipients studied. Future research should clarify fracture incidence and risk, which will inform the design of future prevention trials and guide prognostication.

Secondary and tertiary hyperparathyroidism

We reviewed the etiology and management of secondary and tertiary hyperparathyroidism. Secondary hyperparathyroidism is characterized by an increase in parathyroid hormone (PTH) that is appropriate and in response to a stimulus, most commonly low serum calcium. In secondary hyperparathyroidism, the serum calcium is normal and the PTH level is elevated. Tertiary hyperparathyroidism is characterized by excessive secretion of PTH after longstanding secondary hyperparathyroidism, in which hypercalcemia has ensued. Tertiary hyperparathyroidism typically occurs in men and women with chronic kidney disease usually after kidney transplant. The etiology and treatment of secondary hyperparathyroidism is relatively straightforward whereas data on the management of tertiary hyperparathyroidism is limited to a few small trials with short follow-up.

CKD-mineral and bone disorder management in kidney transplant recipients

Kidney transplantation, the most effective treatment for the metabolic abnormalities of chronic kidney disease (CKD), only partially corrects CKD-mineral and bone disorders. Posttransplantation bone disease, one of the major complications of kidney transplantation, is characterized by accelerated loss of bone mineral density and increased risk of fractures and osteonecrosis. The pathogenesis of posttransplantation bone disease is multifactorial and includes the persistent manifestations of pretransplantation CKD-mineral and bone disorder, peritransplantation changes in the fibroblast growth factor 23-parathyroid hormone-vitamin D axis, metabolic perturbations such as persistent hypophosphatemia and hypercalcemia, and the effects of immunosuppressive therapies. Posttransplantation fractures occur more commonly at peripheral than central sites. Although there is significant loss of bone density after transplantation, the evidence linking posttransplantation bone loss and subsequent fracture risk is circumstantial. Presently, there are no prospective clinical trials that define the optimal therapy for posttransplantation bone disease. Combined pharmacologic therapy that targets multiple components of the disordered pathways has been used. Although bisphosphonate or calcitriol therapy can preserve bone mineral density after transplantation, there is no evidence that these agents decrease fracture risk. Moreover, bisphosphonates pose potential risks for adynamic bone disease.