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Oxalate nephropathy (OXN) is a frequent and underestimated cause of kidney failure in patients undergoing gastric bypass surgery (GBS) and is characterized by hyperoxaluria with massive deposition of calcium oxalate crystals in the renal parenchyma resulting in tubular damage with subsequent interstitial fibrosis. In these patients, hyperoxaluria occurs primarily as a result of increased enteric absorption. It is important to make an early diagnosis and treatment, since once the process of OXN has begun, the evolution towards end stage renal disease (ESRD) is very frequent and can develop quickly.
We present the case of a patient with a history of type III obesity that underwent a GBS that presented a OXN and ESRD, in order to describe this association.
A 47-year-old woman with history of type III obesity (BMI 35 kg/m2) and GBS one year prior to the consultation, presents to ER with symptoms with a two-week history of asthenia, adynamia and decreased urinary output. On physical examination, she had mucocutaneous paleness, uremic breath, and scratching lesions on the lower limbs and abdomen. Laboratory findings: Cr 15mg/dL Urea 270 mg/dL, pH: 7,24, HC03-: 11 mEq/L, Hb: 7,4 g/dL. Renal ultrasound: normal. Complementary studies: electrophoretic proteinogram and rheumatology panel: normal. Viral panel: non-reactive, Proteinuria: 110 mg/day, urinary sediment: 25 isomorphics RBC/HP field. The condition is interpreted as an AKI KDIGO III and initiates emergency hemodialysis. It was decided to perform a renal biopsy, for renal failure of unknown etiology.
RENAL BIOPSY: OM: Glomeruli with expansion of the mesangial matrix. The capillary basement membranes appear thickened and with repeated signs of hypoperfusion. FIAT 35% IF: negative. EM: glomeruli with usual architecture, one with global sclerosis. Without deposits of subendothelial or subepithelial location. The interstitium presents edema. The tubules appear dilated and partially lined by low cuboidal epithelium. Calcium oxalate deposits are recognized in the tubular lumens. Diagnosis: tubular deposits of calcium oxalate associated with tubular distension and acute tubular damage.
OXN is a poorly recognized complication of bariatric surgeries, more frequently associated with Roux Y gastric shunt and to a lesser extent with BAGUA technique. Both consist of the anastomosis of the stomach to the distal small intestine, excluding the duodenum and producing hyperoxaluria secondary to an increase in enteric reabsorption of oxalates by different mechanisms. Given that obesity is a global public health issue, a substantial increase in the number of GBS performed is expected, with a likely significant increase in the incidence of OXN. In patients with acute renal functional impairment and a history of GBS, the differential diagnosis should include OXN, and renal biopsy should be considered to establish the diagnosis and plan treatment strategies that prevent progression to ESRD.