Tuesday, November 2, 2010

TOPIC DISCUSSION: Secondary Oxalate Nephropathy

Primary Hyperoxaluria leading to Oxalate Nephropathy has been noted and well established in the literature. What does one see on biopsy?
Under polarized light, oxalate crystals are doubly refractive and show all colors of rainbow, mostly yellow. With EM, oxalate crystals, appear as mainly long needles with blunt edges. Ca oxalate crystals appear blue in H and E stain and black in Von Kossa's stain.
Usually with acute kidney injury, one sees monohydrate calcium oxalate crystals in renal parenchyma.
Two ways this can happen is either by dietary hyperoxaluria(increased intake) or enteric hyperoxaluria( malabsorption problem leading to increased oxalate bioavailability in the colon).
What about other secondary causes of oxalate nephropathy?
1. Vitamin C overdose
2. Ethylene glycol toxicity
3. Oxalobacter fromigenes, a specific oxalate degrading organism helps regulate oxalate excretion, -- if this organism is less - could lead to it.  ( so prolonged antibiotic use)
4. Malabsorption of fatty acids, leading to increased oxalate bioavailability in the colon. so in jejunoileal bypass patients, extensive small bowel resection, partial gastrectomy patients
5. Increased nuts intake( few cases reported)
6. Orlistat use for weight loss
7. Piridoxilate use
8. Star Fruit ingestion( carambola)
9. Aspergilloma infection

Keep this diagnosis in mind in few cases where it might be important.
( picture on left is of star fruit)

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