Tubular phosphate transport: a comparison between different methods of urine sample collection in FGF23-dependent hypophosphatemic syndromes.

OBJECTIVES: Tubular maximum phosphate reabsorption per glomerular filtration rate (TmP/GFR) is used to evaluate renal phosphate reabsorption and it is a useful tool for the differential diagnosis of hypophosphatemic syndromes. TmP/GFR is typically calculated from fasting plasma and second morning void urine samples, obtained 2 h after the first void (TmP/GFR 2 h). The purpose of this study was to evaluate if TmP/GFR calculated from 24 h urine collection (TmP/GFR 24 h) can be used as an alternative for TmP/GFR 2 h in patients with urine phosphate wasting. METHODS: We enrolled adult patients with X-linked hypophosphatemia (XLH) or tumor-induced osteomalacia (TIO). All patients underwent blood and urine sample collections, to calculate TmP/GFR 24 h and TmP/GFR 2 h. RESULTS: Twenty patients (17 XLH and 3 TIO), aged 24-78 years, were included. All patients had low TmP/GFR 2 h (0.35 mmol/L, IQR 0.24-0.47 mmol/L) and TmP/GFR 24 h (0.31 mmol/L, IQR 0.22-0.43 mmol/L). The concordance correlation coefficient between TmP/GFR 2 h and TmP/GFR 24 h was 0.86 (95 % CI: 0.69-0.93), with a systematic bias of 0.05 mmol/L (95 % limits of agreement: -0.10 to 0.20). Furthermore, in 70 % (i.e., 14 patients out of 20) and 80 % (i.e., 16 patients out of 20) of cases the difference between TmP/GFR 2 h and TmP/GFR 24 h was within ±30 % and ±35 %, respectively. CONCLUSIONS: Despite TmP/GFR 2 and 24 h show a relatively suboptimal agreement, the difference between the two parameters appears to be small and not clinically significant in the setting of adult patients with FGF23-dependent urine phosphate wasting and secondary hypophosphatemia.

Persistent urinary phosphate wasting in a patient with metastatic breast cancer: What's your diagnosis?

Tumor-induced osteomalacia (TIO) can cause severe, persistent hypo-phosphatemia due to high fibroblast growth factor-23 (FGF-23) levels, which lead to uri-nary phosphate wasting. TIO is frequently encountered in association with mesenchy-mal tumors and responds well to resection of the primary malignancy. Rarely, TIO may be seen as a paraneoplastic phenomenon with solid organ malignancies where correction of biochemical abnormalities requires ongoing phosphorus replacement. We report a case of TIO in a patient with metastatic breast cancer complicated by increased parathyroid hormone release secondary to denosumab-induced hypocalcemia. The patient required intensive intravenous and oral phosphate supplementation in addition to vitamin D repletion. A high index of clinical suspicion can yield the correct diagnosis where TIO arises in the setting of a solid organ tumor and help the clinician appropriately manage these challenging cases.

Atypical thymic carcinoid manifesting with nephrotic-range proteinuria in a 7-year-old boy.

BACKGROUND: Nephrotic-range proteinuria as a paraneoplastic syndrome (PNS) is an exceptional presentation, especially in children. It is usually associated with hematologic malignancies. Solid tumors are very rare causes of proteinuria. CASE-DIAGNOSIS/TREATMENT: We present the case of a 7-year-old boy with an extremely rare atypical thymic carcinoid accompanied by nephrotic-range proteinuria as PNS. The kidney biopsy was consistent with minimal change disease (MCD). Tests for a neuroendocrine tumor were performed due to symptoms of hypercortisolemia and an elevated concentration of chromogranin A in the serum. The chest computed tomography revealed a tumor in the anterior mediastinum, which was diagnosed as an atypical thymic carcinoid. A complete resolution of the nephrotic-range proteinuria was observed within 1 week after the first thoracoscopic surgery, with almost complete reduction of the tumor mass. CONCLUSIONS: This extremely rare case shows that MCD can occur as a PNS even in children. Nephrotic-range proteinuria can be a symptom of malignant solid tumor. This case highlights the possibility of secondary causes of MCD in children.

Laboratory approaches for the diagnosis and assessment of hypercalcemia.

Calcium, the fifth most common element in the body, plays major physiological functions. Measurement of blood calcium is one of the most commonly ordered laboratory tests in assessments of calcium homeostasis and disease diagnosis. Hypercalcemia is an increased level of calcium in the blood. This disorder is most commonly caused by primary hyperparathyroidism and malignancy. However, other less common causes of elevated calcium levels need to be considered when making a differential diagnosis. This review is intended to provide readers with a better understanding of calcium homeostasis and the causes and pathophysiology of hypercalcemia. Most importantly, this review describes useful approaches for laboratory scientists and clinicians to appropriately diagnose and assess hypercalcemia.

Hypophosphaturic mesenchymal tumor of the ethmoid associated with oncogenic osteomalacia.

Oncogenic osteomalacia is an uncommon syndrome characterized by bone pain, proximal muscle weakness, hypophosphatemia, hyperphosphaturia, and a low plasma concentration of 1,25-dihydroxy-vitamin D. The disease affects both sexes at around 40 years of age, although it can sometimes affect children and adolescents. Generally, the syndrome is associated with a tumor, usually benign, of mesenchymal origin and is resolved after removal of the tumor; this syndrome can sometimes be associated with malignant tumors. These tumors seem to be histologically heterogeneous and are generally localized in soft tissues and bone. In this article, a case of oncogenic osteomalacia associated with a hypophosphaturic mesenchymal tumor of the ethmoid is reported in a 24-year-old man. After surgical and radical removal of the tumor, the patient noted a decrease in the clinical symptoms and signs.

Aminohydroxypropylidene bisphosphonate (APD) treatment for tumor-associated hypercalcemia: a randomized comparison between a 3-day treatment and single 24-hour infusions.

Intravenous aminohydroxypropylidene bisphosphonate (APD) normalizes serum calcium in most hypercalcemic cancer patients, however the optimal therapeutic scheme has not been established. We compared in a randomized prospective trial the efficacy and the tolerance of APD given as a 3-day treatment of daily 2-h infusions of 0.5 mg/k.d in 250 ml of saline (group A) with single 24-h infusions of 1.5 mg/kg (group B) or of 0.5 mg/kg in 1 liter of saline (group C). Thirty-three cancer patients remaining hypercalcemic after a 48-h rehydration period were included and monitored daily until normocalcemia or treatment failure was documented. Serum calcium became normal in all but 1 patient (in group C) but remained normal for only 1 or 2 days in 4 other patients (1 in A, 1 in B, 2 in C). The decline in total or ionized serum calcium was slightly less marked in group C than in the two other groups, but the differences were not significant. The fall of fasting urinary calcium excretion was however significantly less rapid in group C (p less than 0.05 from day 1 to day 4). Serum concentrations of iPTH and 1,25-dihydroxyvitamin D [1,25-(OH)2D] increased significantly in the three groups. Serum magnesium concentrations fell slightly from 1.41 +/- 0.05 to 1.28 +/- 0.04 mEq/liter (p less than 0.001) after rehydration but returned to normal after APD administration (day 5, 1.52 +/- 0.04 mEq/liter, p less than 0.001 versus day 0).(ABSTRACT TRUNCATED AT 250 WORDS)