Renal osteodystrophy in CAPD.

At start of dialysis most patients have histological bone abnormalities. These can be divided into two groups--high turnover and low turnover bone disease. Low turnover aplastic disease was previously attributed to aluminum accumulation but is now known to occur even in patients with less than 5% surface stainable aluminium. It is characterised by a mineralisation defect, thin osteoid seams, decreased numbers of osteoclasts and osteoblasts and absent aluminium staining. We have avoided aluminium containing phosphate binders (ACPBs) completely, with a combination of oral calcium carbonate and "low calcium" (1.25 mMol/l) dialysis fluid. Phosphate control has been good (mean less than 1.6 mMol/l) and over the first twelve months serum PTH levels have fallen significantly. Transient asymptomatic episodes of hypercalcaemia have occurred but no patient required ACPBs. Bone biopsies at the start of CAPD in 34 patients showed over 50% to have osteitis fibrosa (OF) but in five cases (15.6%) the aplastic lesion was found without aluminium staining. In seven follow-up biopsies OF improved in 3 cases, osteomalacia improved in 1, became aplastic in 1, while aplastic bone worsened in 1 and changed to mild OF in 1. We conclude that the predominant bone lesion in our patients at start of CAPD is OF, but 15% already have aplastic bone. "Low calcium" dialysis fluid enables ACPBs to be avoided in the majority of CAPD patients.