Chronic dietary oxalate nephropathy after intensive dietary weight loss regimen

Acute oxalate nephropathy: A potential cause of acute kidney injury in diabetes mellitus—A case series from a single center

Background

Acute oxalate nephropathy (AON) is an uncommon condition that causes acute kidney injury (AKI), characterized by the massive deposition of calcium oxalate crystals in the renal parenchyma. In previous studies, urinary oxalate excretion has been found to be increased in patients with diabetes mellitus (DM). Here, we report a case series of diabetic patients with AKI with biopsy-proven AON, aiming to alert physicians to the potential of AON as a trigger of AKI in diabetic patients in clinical practice.

Materials and methods

Cases with pathological diagnosis of AON who presented with AKI clinically and had DM between January 2016 and December 2020 were retrospectively enrolled. Their clinical and pathological manifestations, treatment, and prognosis were collected.

Results

Six male patients with biopsy-proven AON out of a total of 5,883 native kidney biopsies were identified, aged 58.3 ± 9.1 years at the time of kidney biopsy. Only one patient who had received Roux-en-Y gastric bypass surgery took oxalate-rich food before the onset of the disease. None of them had clinical features of enteric malabsorption. Three patients were currently on renin-angiotensin system inhibitor treatment for hypertension, and 5 of them received non-steroidal anti-inflammatory drugs. Three patients presented with oliguria and 4 patients needed dialysis at the beginning with none requiring dialysis at discharge. Four patients received a course of corticosteroid treatment empirically. Among them, two patients had estimated glomerular filtration rate (eGFR) recovered to over 60 ml/min/1.73 m2, while the other two patients remained with kidney dysfunction at the last follow-up. In two patients without corticosteroid treatment, one patient fully recovered with eGFR over 90 ml/min/1.73 m2 and the other patient remained with kidney dysfunction at the last follow-up.

Conclusion

AON might be a rare but potentially trigger of AKI in patients with DM. A kidney biopsy could help physicians to make the correct diagnosis. The proper treatment to alleviate oxalate-induced injury needs to be further studied.

Diet-induced oxalate nephropathy from excessive nut and seed consumption

Oxalate is a metabolite consumed in nuts, beans and leaves, and excreted in urine. Oxalosis can cause nephropathy. We describe a rare case of a high-oxalate diet intended for irritable bowel syndrome (IBS) treatment causing oxalate nephropathy. A 59-year-old woman with a history of controlled hypertension presented with creatinine 1.8 mg/dL, increased from baseline 1.3 mg/dL. She denied recent illness, urinary stones, medication adjustments, herbal supplements and non-steroidal anti-inflammatory drugs use. Diet included six tablespoons of chia seeds and five handfuls of almonds daily to manage IBS symptoms. Her electrolytes, urinalysis and renal ultrasound were unremarkable. Her 24-hour urine output revealed increased oxalate and low citrate. Renal biopsy showed glomerulosclerosis, fibrosis and calcium oxalate deposition. She switched to a low-oxalate diet, with improvement in laboratory markers. An earlier dietary history could have raised concern for oxalosis prior to renal biopsy. Providers should be trained to identify at-risk patients and provide appropriate dietary counselling.

Calcium oxalate crystal deposition in the kidney: identification, causes and consequences

Calcium oxalate (CaOx) crystal deposition within the tubules is often a perplexing finding on renal biopsy of both native and transplanted kidneys. Understanding the underlying causes may help diagnosis and future management. The most frequent cause of CaOx crystal deposition within the kidney is hyperoxaluria. When this is seen in native kidney biopsy, primary hyperoxaluria must be considered and investigated further with biochemical and genetic tests. Secondary hyperoxaluria, for example due to enteric hyperoxaluria following bariatric surgery, ingested ethylene glycol or vitamin C overdose may also cause CaOx deposition in native kidneys. CaOx deposition is a frequent finding in renal transplant biopsy, often as a consequence of acute tubular necrosis and is associated with poorer long-term graft outcomes. CaOx crystal deposition in the renal transplant may also be secondary to any of the causes associated with this phenotype in the native kidney. The pathophysiology underlying CaOx deposition is complex but this histological phenotype may indicate serious underlying pathology and should always warrant further investigation.

A diagnostician's field guide to crystalline nephropathies

The kidney's role in filtration of blood and production of urine occurs via a combination of size and charge filtration at the glomerular basement membrane and resorption and excretion of molecules through a complex tubular system embedded within an ion gradient. This delicate system provides the kidney with a unique propensity for substrate saturation and crystal nucleation within the nephron. While crystalline nephropathies may seem exotic to the uninitiated, they are comprised of easily recognizable morphologies and generally lack complicated classification schemas. Additionally, unlike many intrinsic kidney diseases, crystalline nephropathies are often associated with systemic conditions that, upon further investigation, may elucidate critically important information. This review focuses on practical, diagnostically relevant and high yield information that can be utilized by diagnosticians. Our hope is to equip the reader who reviews renal tissue with a practical toolkit that they feel empowered to use when faced with crystal formation in a kidney biopsy, pre-implantation biopsy, or nephrectomy specimen. Short Abstract The kidney's role in filtration of blood and production of urine provides a unique propensity for substrate saturation and crystal nucleation within the nephron. While crystalline nephropathies may seem exotic to the uninitiated, they are comprised of easily recognizable morphologies and generally lack complicated classification. Additionally, crystalline nephropathies are often associated with systemic conditions that, upon further investigation, may elucidate critically important information.

Combining Acute Kidney Injury with Gastrointestinal Pathology: A Clue to Acute Oxalate Nephropathy

Acute oxalate nephropathy (AON) is an increasingly recognized cause of acute kidney injury (AKI). Herein, we present two cases of biopsy-proven acute oxalate nephropathy in patients with gastrointestinal malabsorption, coincidentally both stemming from cholangiocarcinoma. The first is a 73-year-old male who presented with syncope and was found to have severe, oliguric AKI in the setting of newly diagnosed, nonresectable cholangiocarcinoma. The second is a 64-year-old man with remote resection of cholangiocarcinoma who presented after routine laboratory monitoring showed significant AKI. Temporary dialysis was required in both cases before renal recovery occurred. Together, these cases should increase physicians' suspicion of AON in the presence of malabsorption. By doing so, the workup of oxalate nephropathy can be expedited with prompt initiation of treatment.