Renal osteodystrophy

Definition

A disease characterised by multiple abnormalities in calcium metabolism, with secondary hyperparathyroidism, osteomalacia, osteosclerosis, osteoporosis and metastatic calcification.

Aetiology

The dysfunctional kidneys have a decreased ability to 1-hydroxylate the 25-hydroxycholecalciferol.  The resultant deficiency in effective vitamin D leads to decreased calcium absorption and osteomalacia.

The kidney is less able to excrete the phosphate that is presented to it so hyperphosphataemia develops.  Along with the decreased levels of calcium this acts as a stimulus for increased PTH secretion.

PTH breakdown is decreased.

Osteomalacia may be caused not only from the defective production of calcitriol but also from the accumulation of aluminium in the bone.  Aluminium is used as a phosphate binder to decrease serum phosphate in renal failure.  It may cause osteomalacia by inhibition of calcium deposition or by toxicity to the osteoclasts [1].  Iron deposition in patients who have received multiple transfusions can also impair mineralisation of osteoid.

Renal osteodystrophy is often more severe now because patients are kept alive on dialysis for longer.

Clinical

Severe bone pain and tenderness

Pathological fractures

Slipped capital femoral epiphysis in childhood

Ectopic calcification may occur in the conjunctiva, blood vessels, periarticular tissues and skin

Children are affected more than adults and may also be dwarfed.

Laboratory findings

Increased creatinine and urea levels

Normal or low serum calcium

High serum phosphate

High alkaline phosphate

High PTH 

Low vitamin D

Radiology

1. Osteosclerosis
   1. Rugger jersey spine
   2. Dense bones
2. Changes of hyperparathyroidism
   1. Subperiosteal resorption radial side of middle phalanges index and middle fingers
3. Changes of osteomalacia
   1. Looser zones
   2. Softening eg. Trefoil pelvis
4. Metastatic calcification
5. Brown tumours
   1. Indistinguishable from GCT on histology
   2. Diagnosed by multiple tumours, background of renal disease

Treatment

1. Reduction of phosphate with phosphate binders
2. High dose vit D3 (calcitriol)
3. Surgical correction of deformity, fixation of epiphysiolysis for slipped epiphysis
4. If tertiary hyperparathyroidism develops, parathyroidectomy
5. Desferoxamine in patients with aluminium toxicity
6. Renal transplantation