Renal osteodystrophy

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Overview
Renal osteodystrophy is a bone pathology, characterized by defective mineralization, that results from renal disease. renal - refers to kidney, osteo - refers to bone, and dystrophy - means degenerative disorder (like dystrophy in muscular dystrophy).

There are different forms of renal osteodystrophy. Renal osteodystrophy that is characterized by high bone turnover, and renal osteodystrophy that is characterized by low bone turnover.

Signs and symptoms

 * Silent (no symptoms).
 * Bone pain.
 * Joint pain.
 * Bone deformation.
 * Fractures.

Diagnosis
Usually diagnosed after treatment for end-stage renal disease (ESRD) begins.
 * Blood tests - calcium (is decreased), phosphate (is elevated), calcitriol (vitamin D) (is decreased), PTH (is elevated).

Can be recognized on X-ray (but may be difficult to differentiate from other conditions). Features on X-ray:
 * Calcification of cartilage (chondrocalcinosis) - typically at the knees and pubic symphysis.
 * Bone loss - "patchy" appearance (osteopenia)
 * Fractures

Pathogenesis
The mineral content of bone is calcium hydroxyapatite, Ca5(PO4)3(OH). When calcium is being actively resorbed from bone, the phosphate also enters the blood stream. The kidney is the primary means of excreting excess phosphate. Renal osteodystrophy results from an abnormally elevated serum phosphate (hyperphosphatemia) and low serum calcium (hypocalcemia), both of which are due to decreased excretion of phosphate by the damaged kidney, low vitamin D levels or tertiary hyperparathyroidism (a dysfunction of the parathyroid gland due to constant stimulation).

Differential diagnosis

 * osteoporosis
 * osteopenia
 * osteomalacia
 * hyperparathyroidism
 * multiple myeloma
 * soft tissue calcification including collagen vascular disease
 * hydroxyapatite crystal deposition disease
 * hypervitaminosis

Treatment

 * calcium supplementation
 * dietary phosphate restriction
 * vitamin D
 * phosphate binders calcium carbonate (Tums), calcium acetate (PhosLo), sevelamer hydrochloride (Renagel), or lanthanum carbonate (Fosrenol)
 * cinacalcet - a calcimimetic
 * frequent hemodialysis (five times a week) is thought to be of benefit
 * renal transplantation

Prognosis
Recovery from renal osteodystrophy has been observed post renal transplantation. Renal osteodystrophy is a chronic (persistent) condition with a conventional hemodialysis schedule.