**8.4 Renal osteodystrophy**

Renal osteodystrophy is secondary to a combination of bone disorders as a consequence of chronic renal dysfunction, and often shows the most severe cases of metabolic bone disease. It may include osteoporosis, osteomalacia, adynamic bone, and secondary hyperparathyroidism in varying degrees. The most frequent bone scan imagings are similar to a superscan from other metabolic bone disorders, and uptake of diphosphonate in areas of ectopic calcification also may be seen. A lack of bladder activity (secondary to the renal failure) may help in identification and differentiating this type of scintigraphic pattern from others. Aluminum toxicity from hemodialysis, rarely seen now, causes a poor quality bone scan with reduced skeletal uptake and increased soft-tissue activity, as aluminum blocks mineralization and hence the uptake of tracer, resulting in a pattern applicable to all forms of adynamic bone disease. Quantitative measurements of bone metabolism in renal osteodystrophy using 18F-fluoride have been compared with bone histomorphometry and have shown a close relationship between the net plasma clearance of 18F-fluoride to bone mineral and the histomorphometric indices of bone formation. The method was able to differentiate low turnover from high turnover states of renal osteodystrophy (Cook et al., 2010; as cited in Messa et al., 1993).
