The pitfall of treating low bone turnover: Effects on cortical porosity

- We analyzed cortical porosity (Ct.Po) in patients on hemodialysis enrolled in a previous randomized clinical trial.
- Ct.Po was already high at baseline in the majority of patients and correlated with PTH levels, despite turnover status.
- Ct.Po increased after one-year in most patients, and neither gender nor any choice of therapy has affected Ct.Po increase.
- The increase in Ct.Po was significant only in non-white patients and correlated with the delta of PTH.

Although it is recognized that cortical bone contributes significantly to the mechanical strength of the skeleton, little is known about this compartment from bone biopsy studies, particularly in CKD patients. In addition, there is no prospective data on the effects of CKD-MBD therapy on cortical porosity (Ct.Po). This is a post hoc analysis on data from a randomized controlled trial on the effects of different phosphate binders on bone remodelling. Therapy was adjusted according to the first biopsy, and included sevelamer or calcium acetate, calcitriol and changes in calcium dialysate concentration. We measured Ct.Po at baseline and one year after. Fifty-two patients (46 ± 13 years old, 67% women and 60% white) were enrolled. Ct.Po was already high at baseline in 85% of patients [30% (17, 46)] and correlated with PTH (p = 0.001). Low bone turnover was seen in 28 patients (54.9%). After one-year treatment, PTH increased in patients with low turnover, as intended. However, increased Ct.Po was seen in 49 patients (94%). This increase correlated with the delta of phosphate (p = 0.015) and the delta of PTH (p = 0.03); it was also higher among non-white patients than in white patients (p = 0.039). The risk of increase in Ct.Po was 4.5 higher among non-white patients. Adjusted multiple regression analysis showed that the delta of Ct.Po was dependent on delta PTH and race (r2 = 0.193). We concluded that in an attempt to increase bone turnover, the increase in PTH levels might be associated with higher cortical porosity, particularly in non-white patients. Whether this finding leads to a high risk of fracture deserves further investigation.