-2 :: Case - 13136 ::
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Tx and Followup:
Improving post liver transplant

Additional Discussion:
The images reveal severe cortical nephrocalcinosis, osteosclerosis, and renal osteodystrophy. The differential diagnosis for cortical nephrocalcinosis includes renal cortical necrosis, chronic or hereditary glomerulonephritis, and oxalosis, and renal transplant rejection. Consider why this young patient has cortical nephrocalcinosis and has had a liver transplant.

The patient clinically has primary hyperoxaluria ( urine oxalate > 80 mg / day). Primary hyperoxaluria is usually divided into two autosomal recessive diseases: Type 1 (peroxisomal liver AGT enzyme disorder) and Type 2 (cytosolic enzyme disorder). Usually type 2 hyperoxaluria has a mild clinical course (unlike this case).

This patient has Type 1 primary hyperoxaluria (PH1) and "oxalosis." Oxalosis refers to calcium oxalate deposition in tissues other than the kidney which occurs when oxalateretention due to renal failure is added to oxalate over-production due to a metabolic condition.

PH1 is caused by a rare inborn error in liver metabolism (autosomal recessive) in which excessive amounts of oxalic acid are formed which combine with calcium and deposit throughout the body (kidney, soft tissue, bone). The hepatic peroxisomal enzyme AGT (alanine:glyoxylate aminotransferase) is defective and glyoxylate cannot be converted into glycine; hence, excessive glyoxylate is metabolized into oxalate.

This disorder leads to progressive renal failure secondary to cortical nephrocalcinosis which usually leads to early death in childhood unless dialysis is instituted. Common radiographic findings in oxalosis include dense kidneys (nephrocalcinosis), dense bones (calcium oxalate crystal deposition and renal osteodystrophy), soft tissue and vascular calcifications, and radiopaque renal calculi. Treatment includes pyridoxine, dialysis, and liver transplant to replace the defective AGT enzyme.

Discussion Author: Ultrasound Learning File - © ACR

The term oxalosis refers to the condition in which the highly insoluble calcium oxalate crystals are deposited in extrarenal tissues including bone, cartilage, blood vessels, heart, central nervous system, peripheral nerves, and the male genitourinary system. Oxalosis is not commonly due to primary hyperoxaluria. Secondary hyperoxaluria is a less common cause of oxalosis. Primary hyperoxaluria is a rare metabolic disorder characterized by excessive synthesis and urinary excretion of oxalate.

There are two types of primary hyperoxaluria, both of which are transmitted as autosomal recessive traits. Type I hyperoxaluria is the most common form. It is due to deficiency in an enzyme that metabolizes glyoxylate resulting in excessive synthesis of oxalate and glycolate, which are excreted in the urine. Type II hyperoxaluria is rare. Secondary hyperoxaluria less commonly results in cortical nephrocalcinosis and/or nephrolithiasis. Ileal disease, including Crohn's disease, ileal bypass or resection, and the blind loop syndrome, is the most common cause of secondary hyperoxaluria. Ileal dysfunction results in fat malabsorption, resulting in an increase in the intraluminal fat concentration. Calcium binds to this intraluminal fat forming calcium-fatty acid soaps. Less calcium is available to bind with oxalate, resulting in excess absorption of free oxalate. Other causes of secondary hyperoxaluria include excessive ingestion of oxalate or of its precursors, especially in green leafy vegetables such as spinach and rhubarb; pyridoxine deficiency; exposure to methoxyflurane anesthesia; and ethylene glycol ingestion.

There are two basic clinical presentations of primary hyperoxaluria, although a spectrum of disease exists. The typical patient presents with recurrent nephrolithiasis in childhood leading to progressive renal insufficiency and renal failure in early adulthood. Symptoms due to renal calculi develop before age 5 years in 65% of cases. Renal failure results from severe interstitial nephritis due to oxalate deposits. Death from uremia usually develops before or during the third decade, with an 80% mortality by age 20. There is a less common infantile presentation which is characterized by nephrocalcinosis without nephrolithiasis, leading to chronic renal failure in infancy or very early childhood.

The distribution of crystal deposition is most closely related to organ vascularity, with the kidneys invariably involved. Renal damage results from a combination of cortical nephrocalcinosis, nephrolithiasis, and secondary interstitial fibrosis. The classic sonographic findings include normal to small sized kidneys with increased cortical echogenicity and relatively preserved corticomedullary differentiation. Calcium oxalate stones may cause shadowing in the renal cortex or collecting system. Ultrasound and CT are more sensitive in the detection of calcification within the renal cortex and collecting system than plain radiography.

The differential diagnosis of increased renal cortical echogenicity with preservation of the corticomedullary junction in an infant, child, or young adult includes renal vein thrombosis, amyloidosis, leukemic infiltration, and other causes of cortical nephrocalcinosis (chronic glomerulonephritis, Alport's syndrome, acute cortical necrosis). Other clinical manifestations include arthritis, cardiac conduction defects, localized ischemic skin lesions, and peripheral neuropathy. The treatment of choice is renal transplantation. Hemodialysis may prolong survival but does not result in the removal of oxalate from the blood or tissues.

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