MO772PRIMARY AND SECONDARY HYPEROXALURIA IN CHRONIC DIALYSIS PATIENTS: FOCUS ON VASCULAR ACCESS

Background and Aims Hyperoxaluria is a rare metabolic disorder chacterized by widespread calcium oxalate deposition, if plasmatic oxalate level (pOx) overcomes saturation threshold. It could be primary (PH), a recessive disease associated with mutation of the liver enzyme LDH, or secondary (SH), in 75% due to intestinal malabsorption. Urolithiasis could be the first complication, and renal involvement could progress until end-stage renal disease (ESRD). Mean pOx is higher in chronic dialysis patients than healthy individuals because of impaired renal clearance. Oxalate molecular weight (MW) is 88 Da and its clearance is that of low MW uremic toxins. Our aim is to assess an association between arteriovenous fistula (AVF) failures and Hyperoxaluria. Method In the period between 1/1/2004 and 12/31/2020, diagnosis of Hyperoxaluria was carried out in 6 patients out of 1530 chronic dialysis patients (0.39%). The median age of patients was 65.5 [26-72] years, the male/female ratio was 3:3 and the median dialysis vintage was 36 [1-181] months. Three patients come to nephrological referral at stage 5 of CKD while 1 patient came to Italy when chronic HD was already started. At that time pOx was not considered. In these 4 patients the presumptive diagnosis of ESRD was urolithiasis and diagnosis of Hyperoxaluria was carried out after the beginning of chronic dialysis, when pOx and genetic analysis were performed. In 1 case biopsy on the kidney graft and in 1 case kidney biopsy after nephrectomy were performed: oxalate deposition was detected. For 2/6 patients diagnosis was carried out after biopsy of native kidneys before starting dialysis. All patients started medical therapy for hyperoxaluria. Five out of 6 patients were eligible to HD, 1/6 to PD. AVF was judged the first choice vascular access. Results PH was diagnosed in 3/6 patients: mutations were detected on chromosome 2. Malabsorption secondary to short bowel syndrome and chronic pancreatitis could be assumed as causes of SH in 3 patients. Patient 1 underwent 2 combined liver-kidney transplantation: the first failed by arterial grafts thrombosis and the second by renal primary non-function but the liver was still functioning, he died on HD after 12 years. Patient 2 underwent liver and kidney transplantation and she is nowadays dialysis-free. The median pOx pre-dialysis and before diagnosis was 165 [98-259] umol/L (Table 1). Patients on chronic HD underwent median of 3 [2-5] AVF interventions. Nine AVFs were distal and 4 were proximal. The most frequent complication was AVF thrombosis despite ASA treatment: half of the cases showed secondary AVF non-function, the other half of AVFs failed to mature. Six tunneled cuffed permanent catheters (TCCs) as definitive vascular access were successfully placed in the 5 patients on chronic HD. Warfarin therapy was started to avoid TCCs thrombosis. The median survival of TCCs was 9.5 [3-48] months. All the patients had a history of deep venous thrombosis (DVT). Conclusion To our knowledge this is the first case series of multiple AVF failures in patients with hyperoxaluria. In our experience TCCs show longer survival then AVF in this group of patients, even if it could not be excluded the role of warfarin in favoring this result. Even though a link between hyperoxaluria and thrombosis is well established, the exact underlying mechanism is still uncleared. The role of PD as dialysis technique of “first choice” should be enhanced also when residual renal function is abolished. In ESRD patients with urolithiasis, diagnosis of Hyperoxaluria should be ruled out before AVF placement.