HYPEROXALURIA

By Gary M. White, MD


Hyperoxaluria is the presence of excessive oxalate in the urine. Primary hyperoxaluria is most commonly caused by one of two inherited defects: inherited deficiency of hepatic alanine:glyoxylate aminotransferase (AGT) in primary hyperoxaluria type 1 and glyoxylate reductase/hydroxypyruvate reductase (GRHPR) in primary hyperoxaluria type 2 (PH2). Both of these result in marked overproduction of oxalate by the liver. Oxalate cannot be metabolized in the human body, thus the excess oxalate must be eliminated, largely by the kidneys, resulting in marked hyperoxaluria.

Secondary oxalosis may occur from excessive intake of oxalate precursors (e.g. ethylene glycol poisoning, methoxyflurane anesthesia, intravenous glycerol or xylitol infusion, or large doses of ascorbic acid) or impaired renal excretion (e.g. end-stage renal failure) or pyridoxine deficiency. In both, calcium oxalate crystals may be deposited in the skin, bones, kidney, myocardium, blood vessels and CNS. Arrhythmias, arthralgias and nephrolithiasis may occur. Secondary oxalosis from CRF or hemodialysis rarely affects the skin. When it does however, it usually presents as calcified papules distal, palmar aspects of all fingers.

Clinical

Livedo reticularis, peripheral necrosis, leg ulceration, and acral nodules or necrotic lesions are characteristic. Primary hyperoxaluria may present in childhood and the inheritance is AR. The majority of patients present with signs and symptoms related to nephrolithiasis by age 5. Rarely, patients with primary hyperoxaluria may make it into adulthood undiagnosed. They may then suffer from renal failure and resultant systemic oxalosis which may cause cutaneous necrosis mimicking calciphylaxis.

Diagnosis

The serum oxalate level should be measured for diagnosis. Alternatively, the urinary oxalate and glyoxylate may be measured if kidney function is intact. If not, enzymatic analysis of liver tissue after percutaneous liver biopsy is possible. Birefringent yellow-brown crystals may be found within arteries and in other tissues.

Treatment

Therapy includes diet regulation, magnesium oxide and phosphate therapy and enzyme inhibitors to decrease oxalate synthesis and excretion. Orthophosphate and pyridoxine appear to preserve renal function in patients with primary hyperoxaluria.

References

An adult man presented with several hyperkeratotic nodules under the fingernails. He suffered from end-stage renal disease and had undergone three kidney transplantations. A recent urinary analysis showed urine oxalates of 93 mg/day (normal limits (10–35 mg/day). Previous genetic testing for primary oxaluria-related enzyme deficiencies was negative, and a diagnosis of secondary hyperoxaluria was made by the patient’s nephrologists. Acta Dermato-Venereologica 2010;91;195-6

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