Parathyroid hormone‐independent osteoclastic resorptive bone disease: a new variant of adynamic bone disease in haemodialysis patients

Abstract

Osteitis fibrosa cystica (OFC) caused by secondary hyperparathyroidism is the pre-eminent form of uraemic osteodystrophy. In recent years, however, new bone abnormalities have been described. Among them adynamic bone disease (ABD) has become a focus of growing interest. Marked suppression of dynamic bone measurements with normal or near-normal static bone-forming parameters are the hallmarks of this disorder. Depressed parathyroid hormone (PTH) levels, frequently evident in this entity, have been linked causally with low bone turnover. We reviewed bone biopsy specimens from 96 patients with end-stage renal disease undergoing chronic haemodialysis. We found OFC in 50% of our patients, 20% had mixed bone disease, 24% showed bone morphology of ABD and a minority (6%) had osteomalacia, mostly due to aluminium accumulation. In the patients that were affected by ABD there was a distinct subgroup with bone morphology featuring a striking increase in osteoclast number and osteoclast surface, whereas the osteoid volume, osteoid thickness, osteoblast surface, tetracycline uptake and bone formation rates were diminished as in ordinary ABD. Similarly the PTH levels in this subgroup were low or undetectable. We describe patients undergoing chronic haemodialysis with static and dynamic bone forming parameters, indistinguishable from that of ABD, but differing from the classic ABD by the presence of increased osteoclastic bone resorption. The suppressed PTH levels in this subgroup suggests that factors other than PTH activate osteoclasts in some patients on chronic haemodialysis. Uraemic cytokines and/or toxic metabolites, including beta-microglobulin, may be involved in this disorder. The precise nature of this bone abnormality remains to be defined by further studies.