Renal Osteodystrophy

 

·        Constellation of musculoskeletal abnormalities occurring with chronic renal failure featuring some combination of

o       Osteomalacia (adults)

o       Rickets (children)

o       2° hyperparathyroidism

o       Soft-tissue calcifications

o       Osteosclerosis

o       Soft-tissue + vascular calcifications

·        Low calcium levels lead to osteomalacia

o       Additional factors responsible for osteomalacia are

§         Inhibitors to calcification produced in the uremic state

§         Aluminum toxicity

§         Dysfunction of hepatic enzyme system A

§         Renal insufficiency with diminished filtration results in phosphate retention

·        Maintenance of Ca x P product lowers serum calcium directly, which in turn increases parathyroid hormone production (2°hyperprathyroidsim)

·        Osteopenia

o       Combined effect of

§         Osteomalacia (reduced bone mineralization due to acquired insensitivity to vitamin D / antivitamin D factor)

§         Osteitis fibrosa cystica (bone resorption)

§         Osteoporosis (decrease in bone quantity)

o       Complications

§         Fracture predisposition (lessened structural strength) with minor trauma

·        Spontaneously

§         Fracture prevalence increases with duration of hemodialysis + remains unchanged after renal transplantation

·        Sites of fractures

o       Vertebral body (3-25%)

o       Pubic ramus, rib (5-25%)

o       Milkman fracture / Looser zones (in 1%)

o       Metaphyseal fractures

o       Prognosis

§         Osteopenia may remain unchanged / worsen after renal transplantation + during hemodialysis

·        Secondary hyperparathyroidism

o       Cause

§         Inability of kidneys to adequately excrete phosphate leads to hyperplasia of parathyroid chief cells (2° hyperparathyroidism)

§         Excess parathyroid hormone affects the development of osteoclasts, osteoblasts, osteocytes

o       Hyperphosphatemia

o       Hypocalcemia

o       Increased PTH levels

o       Subperiosteal, cortical, subchondral, trabecular, endosteal, subligamentous bone resorption

o       Osteoclastoma = brown tumor = osteitis fibrosa cystica (due to parathyroid hormone -stimulated osteoclastic activity

§         More common in 1° hyperparathyroidism

o       Periosteal new-bone formation (8-25%)

o       Chondrocalcinosis

§         More common in 1° hyperparathyroidism)

·        Osteosclerosis (9-34%)

o       One of the most common radiologic manifestations

§         Most common with chronic glomerulonephritis

o       May be the sole manifestation of renal osteodystrophy

o       Diffuse chalky density

o       Thoracolumbar spine in 60% with dense end-plates produce appearance of rugger-jersey (rugger jersey spine)

 

 Rugger-jersey spine in
Renal osteodystrophy

o       Also in pelvis, ribs, long bones, facial bones, base of skull (children)

o       Prognosis

§         May increase/regress after renal transplantation

·        Soft-tissue calcifications

o       Metastatic secondary to hyperphosphatemia (solubility product for calcium + phosphate exceeds 60-75 mg/dL in extracellular fluid)

§         Hypercalcemia

§         Alkalosis with precipitation of calcium salts

o       Dystrophic secondary to local tissue injury

§         Location

·        Arterial (27-83%)

o       In medial + intimal elastic tissue

§         Dorsalis pedis a., forearm, hand, wrist, leg

o       Pipestem appearance without prominent luminal involvement

·        Periarticular (0-52%)

o       Multifocal

o       Frequently symmetric

o       May extend into adjacent joint

o       Chalky fluid / pastelike material

o       Inflammatory response in surrounding tenosynovial tissue

o       Discrete cloudlike dense areas

§         Fluid-fluid level in tumoral calcinosis

o       Prognosis

§         Often regresses with treatment

·        Treatment

o       Decrease of phosphorus absorption in bowel

o       Vitamin D3 administration (if vitamin D resistance predominates)

o       Parathyroidectomy for 3° hyperparathyroidism (= autonomous hyperparathyroidism)

 

Dahnert 5^th edition