Secondary oxalosis of bone in a dialysis patient

Bone oxaloma-a localized manifestation of bone oxalosis

Oxalosis is a metabolic disorder characterized by the accumulation of calcium oxalate deposits in various organ systems. Bone oxalosis is a systemic manifestation of oxalosis, in which calcium oxalate deposits accumulate in the skeletal system. This report describes a 69-year-old female patient who presented with right hip pain and was later found to have an osseous mass-like lesion in the right proximal femur, with radiographic findings resembling those of a benign bone tumor. CT-guided biopsy and surgical biopsy showed that the mass had pathologic findings typical of bone oxalosis. Because the patient had no predisposing factors for systemic oxalosis and had no hyperoxalemia or hyperoxaluria, she could be diagnosed with localized bone oxalate deposition disease or bone oxaloma rather than bone oxalosis. This is the first report of this clinical entity to present as a benign-appearing bone mass and without any predisposing systemic causes.

Vitamin B6 and oxalic acid in clinical nephrology

OBJECTIVE

Vitamin B(6) (VB(6)) is a water-soluble vitamin, which is important for the normal functioning of multiple organ systems. It is metabolized to the active molecule pyridoxal-5-phosphate (PLP). Oxalic acid (OA) is thought to be a uremic toxin that participates in the pathogenesis of the uremic syndrome. The objectives of this study were as follows: (1) to evaluate the plasma and erythrocyte VB(6) (effect of PLP; effect of PLP was in indirect relationship with the concentration of erythrocyte VB(6)), and plasma and urinary OA in marathon runners, in patients with acute intermittent porphyria (AIP) and variegate porphyria, and in patients with stage 1 chronic kidney disease (CKD), chronic glomerulonephritis and nephrotic syndrome (CGNS); (2) to examine the influence of water diuresis in healthy subjects, and the influence of sodium diuresis (high sodium intake) and an intravenous administration of furosemide on the urinary excretion of VB(6) and OA in CKD stage 3-4 patients; and (3) to evaluate the influence of erythropoietin treatment on erythrocyte VB(6) (effect of PLP) in hemodialysis (HD) patients, and the influence of continuous ambulatory peritoneal dialysis (CAPD) therapy on plasma VB(6) and OA and their peritoneal clearance and transfer.

DESIGN AND SETTING

This study was conducted at the Nephrological Clinic of L. Pasteur Faculty Hospital and of Medical School of P. J. Safarik University. A combination of 29 marathon runners, 15 patients with CG and NS, 11 patients with AIP, 1 patient with variegate porphyria, 15 healthy subjects, 27 CKD stage 3-4 patients, 30 HD, and 27 CAPD patients were used in the study.

RESULTS

After a marathon run, plasma and erythrocyte VB(6) significantly decreased and plasma OA increased. Plasma (15.5 +/- 3.8 nmol/L) and erythrocyte VB(6) (effect of PLP: 42.1% +/- 7.5%) were decreased and plasma OA (9.8 +/- 2.3 micromol/L) was significantly elevated in patients with CGNS and stage 1 CKD. In patients with AIP, deficiency of plasma (24.3 +/- 5.2 nmol/L) and erythrocyte VB(6) (effect of PLP: 46.2% +/- 7.0%) and hyperoxalemia (9.39 +/- 2.5 micromol/L) were present. The urinary excretion of VB(6) and of OA during maximal water diuresis and after intravenous administration of furosemide increased significantly (P < .01), but was not affected by the high intake of NaCl (P > .05). Erythropoietin treatment in HD patients led to the erythrocyte VB(6) deficiency. This finding is an indirect evidence that erythrocyte VB(6) is consumed by the hemoglobin synthesis much more during EPO treatment. In CAPD patients, plasma value of VB(6) (127.3 +/- 66.9 micromol/L) was in the normal range and plasma OA (23.6 +/- 7.4 micromol/L) was significantly elevated. Mean value of peritoneal clearance of VB(6) was 8.8% and of OA was 76.9% of urea clearance.

CONCLUSION

Our study indicates that deficiency of VB(6) led to hyperoxalemia and hyperoxaluria in patients with CKD. Deficiency of VB(6) in CKD stage 4-5 patients potentiates the uremic hyperoxalemia and hyperoxaluria.

Oxalic Acid as a uremic toxin

OBJECTIVE

Oxalic acid (OA) is thought to be a uremic toxin that participates in the pathogenesis of uremic syndrome. The objectives of this study were to: (1) evaluate the plasma levels of OA in patients with chronic renal disease with various levels of glomerular filtration rate and after renal transplantation; (2) investigate the salivary secretion of OA and ascorbic acid in healthy subjects and in patients with chronic renal failure (CRF); (3) examine the influence of water and sodium diuresis and furosemide administration on the urinary excretion of OA and ascorbic acid in healthy subjects and in CRF patients without dialysis treatment; and (4) evaluate the influence of renal replacement therapy (RRT) on secondary hyperoxalemia in hemodialysis patients.

DESIGN AND SETTING

This study was conducted at the Nephrological Department of P.J. Safárik University. Sixty-one patients with chronic renal disease, 64 CRF patients, 32 continuous ambulatory peritoneal dialysis (CAPD) patients, 15 hemodialysis patients, 21 patients after renal transplantation, and 15 healthy subjects were examined. Maximal water diuresis, diets with low (2 g/day) and high (15 g/day) sodium intake, administration of intravenous furosemide (20 mg), and renal replacement therapy (CAPD, hemodialysis, hemofiltration, and postdilution hemodiafiltration) were utilized in the study.

RESULTS

In patients with chronic renal disease and those after renal transplantation, direct relationships between plasma OA and serum creatinine were found (r = 0.904 and 0.9431, respectively, P < .01). Despite a high level of plasma OA in uremic patients (23.1 +/- 10 micromol/L), there was no significant difference in salivary OA between control subjects (128 +/- 19 micromol/L) and CRF patients (135 +/- 24 micromol/L). The urinary excretion of OA during maximal water diuresis (from 37.5 to 110.3 micromol/4 hours) and after intravenous furosemide (from 34.5 to 66.7 micromol/3 hours) increased significantly, but was not affected by high intake of NaCl. The most significant decrease of plasma OA was observed during postdilution hemodiafiltration (63.3%).

CONCLUSION

Our study indicates that renal replacement therapy is not effective for a permanent reduction of elevated plasma levels of OA.

Calcium oxalate saturation in dialysis patients with and without primary hyperoxaluria

Calcium oxalate supersaturation of the blood is associated with deposition of crystals in various tissues. We measured the serum levels of oxalate, citrate, calcium, and magnesium to estimate their saturation in 112 hemodialysis patients without primary hyperoxaluria and two boys with primary hyperoxaluria. Serum levels of oxalate and citrate were determined by high-performance capillary electrophoresis, while calcium and magnesium were measured by ICP spectroscopy. The serum levels of oxalate, citrate, calcium, and magnesium were 44.9+/-16.5, 138.1+/-54.9 micromol/l, 2.30+/-0.28, and 1.07+/-0.18 mmol/l, respectively, while the levels in patients with primary hyperoxaluria were 83.9+/-34.3, 197.9+/-63.5 micromol/l, 2.53+/-0.15, and 1.14+/-0.34 mmol/l, respectively. Serum calcium oxalate saturation (SS), as calculated by the Equil program, was significantly correlated with the serum oxalate level. Most patients showed metastable supersaturation (1<SS<8.9), which was associated with a serum oxalate level of more than 30 micromol/l. Serum saturation exceeded the formation product (SS=8.9) in some specimens from patients with type 1 primary hyperoxaluria. The serum calcium oxalate saturation [SS(CaOx)] showed a significant positive correlation with the levels of oxalate [Ox], calcium [Ca], and citrate [Cit]: [SS(CaOx)]=-0.3562+34.634[Ox]+0.394[Ca]-0.483[Mg]+0.101[Cit], (all mmol/l, r=0.9848, P<0.01). This formula is useful for estimating the saturation. In conclusion, the serum oxalate level is a good indicator of calcium oxalate saturation and should be monitored accurately while keeping it lower in dialysis patients.

Long-term, low-dose, intravenous vitamin C leads to plasma calcium oxalate supersaturation in hemodialysis patients

BACKGROUND

Ascorbate supplementation for patients on regular dialysis treatment (RDT) is advised to obviate deficiency and improve epoetin response in those with functional iron deficiency. However, clear-cut safety concerns regarding hyperoxalemia are still poorly understood. This study tries to establish safety/efficacy profiles of ascorbate and oxalate during long-term intravenous ascorbate supplementation.

METHODS

A prospective study was performed in 30 patients on RDT showing ascorbate deficiency (plasma ascorbate < 2.6 mg/L [<15 micromol/L]): 18 patients were administered intravenous ascorbate during 18 months (250 mg/wk, subsequently increased to 500 mg), and 12 patients were taken as reference untreated cases. Plasma ascorbate and oxalate assays and dialytic balance determinations were performed (ion chromatography and reverse-phase high-performance liquid chromatography, respectively) at baseline, during treatment, and 12 months after withdrawal.

RESULTS

Plasma ascorbate levels increased dose dependently with supplementation (1.6 +/- 0.8 mg/L [9.1 +/- 4.6 mumol/L] at baseline, 2.8 +/- 1.8 mg/L [15.9 +/- 10.1 micromol/L]) with 250 mg of ascorbate, and 6.6 +/- 2.8 mg/L [37.5 +/- 16.0 micromol/L] with 500 mg/wk of ascorbate), but only normalized with greater dosages for several months in 94% of patients. Baseline plasma oxalate levels increased from 3.2 +/- 0.8 mg/L (35.8 +/- 8.8 micromol/L) to 3.6 +/- 0.8 mg/L (39.5 +/- 9.1 micromol/L) and 4.5 +/- 0.9 mg/L (50.3 +/- 10.4 micromol/L) with 250 and 500 mg, respectively ( P < 0.001). The calcium oxalate saturation threshold was exceeded by 7 of 18 patients (40%) during 6 months therapy with 500 mg/wk. Ascorbate dialysis removal increased from 37.8 +/- 23.2 mg (215 +/- 132 micromol) to 99.6 +/- 51.7 mg (566 +/- 294 micromol) during supplementation (P < 0.001), with corresponding increases in oxalate removal from 82.5 +/- 33.2 mg (917 +/- 369 micromol) to 111.2 +/- 32.6 mg/L (1,236 +/- 362 micromol; P < 0.01). Withdrawal reverted plasma levels and dialysis removal to initial values. Values for untreated patients did not change during 1 year of follow-up.

CONCLUSION

Patients on RDT may resolve ascorbate deficiency with intravenous supplementation of 500 mg/wk, but this implies a significant risk for oxalate supersaturation. Oxalate measurements are strongly recommended during long-term ascorbate therapy.