Background: Oxalate nephropathy is a potentially underestimated cause of kidney failure characterized by massive deposition of calcium oxalate crystals in the renal parenchyma. The prevalence and modes of presentation of this entity are ill-defined. Methods: Here we report on the largest consecutive series of cases of adult oxalate nephropathy diagnosed on native kidney biopsies from January 2010 to December 2018 in the UCLouvain Kidney Disease Network. Results: We screened 2265 native kidney biopsies and identified 22 cases (1%) of oxalate nephropathy. Patients had a mean age at diagnosis of 61 years (AE20) and presented either with acute on chronic kidney disease (CKD) (62%) or with acute kidney injury (AKI) (38%). Mean serum creatinine at biopsy was 8.0 AE 4.5 mg/dl. Kidney biopsies showed abundant calcium oxalate crystal deposits, associated with acute interstitial nephritis and tubular necrosis, and variable degrees of interstitial fibrosis and tubular atrophy. Chronic pancreatitis and gastric bypass were the most common causes of oxalate nephropathy (48%). During a mean follow-up of 29 months, half of the patients (52%) progressed to kidney failure, all within the month following diagnosis. Higher serum creatinine level at presentation and interstitial fibrosis and tubular atrophy score were associated with progression to kidney failure. Conclusion: Oxalate nephropathy is the cause of kidney disease in 1% of consecutive native kidney biopsies and typically presents as acute on CKD or AKI. The prognosis of the disease is poor, with a high rate of kidney failure within the first month after the diagnosis.

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Background: Isoniazid is the most widely used anti-tuberculosis agent, yet it may lead to life-threatening complications. Case presentation: Here we report the case of a chronic hemodialysis patient who developed severe encephalopathy after the start of isoniazid. Blood levels of isoniazid were elevated, and acetyl-isoniazid over isoniazid ratio was decreased 3 h after intake of the medication, suggesting that a slow acetylator phenotype may have contributed to drug toxicity, in addition to pyridoxal phosphate removal by dialysis. This hypothesis was confirmed by sequencing of NAT2, the gene responsible for isoniazid elimination, and identification of NAT2 polymorphisms compatible with a slow acetylator phenotype. Isoniazid withdrawal along with supplementation using high doses of pyridoxine successfully reversed the drug toxicity. Isoniazid toxicity occurs in populations at risk, including patients with chronic kidney failure or NAT2 polymorphisms, who have a disturbed metabolism of pyridoxine or isoniazid, respectively, and those on renal replacement therapies, in whom pyridoxal phosphate -the active metabolite of pyridoxine -is inadvertently removed by dialysis. Conclusions: Physicians should be aware of the increased risk of isoniazid toxicity in patients on dialysis and in those with a slow acetylator phenotype conferred by NAT2 polymorphisms. Adaptation of prescription -either with higher doses of pyridoxine or decreased doses of isoniazid, respectively -has been suggested to reduce the risk of potentially life-threatening toxicity of isoniazid.