18-Fluorodeoxyglucose positron emission computed tomography for systemic oxalosis in primary hyperoxaluria type 1

Abstract

To the Editor: Primary hyperoxaluria type 1 (PH1) is associated with hepatic overproduction of oxalate. Kidneys gradually become unable to eliminate excess oxalate, leading to systemic oxalosis (SO) with deposits in organs.1 When kidney transplantation (KT) becomes necessary, this oxalate load can lead to oxalate nephropathy recurrence. We report the potential interest of 18-fluorodeoxyglucose positron emission computed tomography (18-FDG-PET/CT) as a tool to assess SO in PH1 patients. Signed informed consent was obtained. Patient 1,2 a 16-year-old anuric PH1 male patient, on hemodialysis (HD) since 4 years, was admitted for liver transplantation (LT). Plasma oxalate (POx) and calcium levels were 62 µmol/L (normal: 3–11) and 3.01 mmol/L (normal: 2.10–2.55), respectively. Because of chronic diffuse body pain, 18-FDG-PET/CT was performed before LT. Multiple metabolic spots in bones were observed with maximal standardized uptake values (SUVmax), ranging from 3.6 to 11.9 (liver SUVmean/max in 3cm diameter sphere: 1.4/2.2) as well as nephrocalcinosis with some calcifications showing intense metabolism (Figure 1A). Infection/tuberculosis, hyperparathyroidism and cancer were excluded. We hypothesized that these images and hypercalcemia were consistent with an inflammatory reaction secondary to calcium oxalate deposits. Unfortunately, LT complicated and the patient died before KT could be performed. Patient 2 is a 36-year-old PH1 male patient on nocturnal HD since 2 years when he received a LT. Two months later, 18-FDG-PET/CT performed for malaise showed multiple metabolic spots in bones (SUV 3.0 to 7.5, liver SUVmean/max in 3 cm diameter sphere: 1.97/3.0). Bilateral massive nephrocalcinosis was also visible with diffuse metabolism (Figure 1B—Baseline). One year after LT, he received a kidney graft. POx level was 39 µmol/L; he was anuric. Daily HD was undertaken for 5 weeks. A graft biopsy performed 3 months after KT for elevated creatinine (2 mg/dl [Normal < 1.2]) showed oxalate nephropathy recurrence. Bone marrow biopsy revealed massive deposits of oxalate calcium crystals. HD was re-initiated for 5 months. Thereafter, creatinine remained stable (2.2 mg/dl). However, urine oxalate levels remained high for 2 years (>100 [Normal < 32] mg/g of creatinine on urinary spot) before decreasing to normal values. Three years after KT, 18-FDG-PET/CT showed disappearance of metabolic bone spots, and improvement of nephrocalcinosis (Figure 1B—Follow-up). Because he was anuric before KT, we hypothesized that oxalate from bone and kidneys mobilized into the blood at KT and participated in the allograft oxalate precipitation. These two cases suggest that 18-FDG-PET/CT might be useful (1) as a non-invasive diagnostic tool for assessing SO in PH1 patients—as previously suggested,3 (2) to follow in time the clearance of oxalate from the bone and kidneys. Also, our data suggest systemic mobilization of oxalate calcium deposits from the kidneys after restauration of renal function, implying that the removal of native kidneys might make sense to protect the graft from oxalate rush. Innovative drug such as RNA interference drugs,4, 5 have brought hope of LT avoidance. Nevertheless, accurate assessment of SO remains critical to determine the best timing for performing KT. 18-FDG-PET/CT might be useful and deserves further investigation. The potential interest of this technique in secondary hyperoxaluria should also be explored. The authors of this manuscript have conflicts of interest to disclose as described by the American Journal of Transplantation. Arnaud Devresse and Nathalie Godefroid declare fees from Alnylam.