Apreviously healthy 46-year-old man with 5-month history of T5-T6 level paraplegia after a motor vehicle accident was admitted to the spinal cord rehabilitation center. The patient was found to have persistent hyperphosphatemia in the range of 6.5 to 6.7 mg/dL during routine laboratory evaluations. His phosphorus (Pi) level was previously normal (3.1 mg/dL) at the time of the motor vehicle accident. Physical examination was remarkable for T5-T6 level paraplegia and left elbow calcification. The patient was also found to have mildly elevated serum calcium (Ca) (10.4 mg/dL), suppressed parathyroid hormone (PTH) (10 pg/mL) and elevated fibroblast growth factor-23 (FGF-23) (263 RU/mL). Additional laboratory data are shown in Table 1. The oral intake consisted of 1 L of "Peptamen" bolus tube feeding containing 667 mg of Pi per liter. The patient was not taking any medications or oral supplements. sevelamer carbonate 2.4 g with meals was initiated to reduce intestinal absorption. No improvement in serum Pi levels was observed with sevelamer carbonate, and it was subsequently discontinued. Because of suppressed PTH levels, PTH-dependent Pi excretion using synthetic PTH was assessed. Fractional excretion of phosphate (FePO4) was measured before and after intravenous administration of 60 mg of teriparatide. Pre- and post-teriparatide FePO4 were 14.01% and 28.22%, respectively, confirming appropriate tubular responsiveness to PTH. Bone-specific markers demonstrated increased bone resorption (N-telopeptide to creatinine ratio was 248 with normal range of 3–51) and bone turnover (bone-specific alkaline phosphatase was 24.7 μg/L with normal range of 0–20.1 μg/L) values that are characteristic for immobilization. The patient was initiated on oral alendronate 70 mg weekly and 3 weeks later, levels of serum Ca and Pi normalized to 8.4 mg/dL and 3.2 mg/dL, respectively. Normalization of Ca and Pi levels led to increased PTH (100 pg/mL), reduction of N-telopeptide to creatinine ratio (112), and normalization of bone-specific alkaline phosphatase (20 μg/L) (Table 1).
Table 1Baseline and follow-up laboratory findings
|Laboratory Data||December 2012||February 2013||May 2013|
|Serum calcium (normal range, 8.5–10.2), mg/dL||10.4||10.3||8.4|
|Ionized calcium (normal range, 1–1.35), mmol/L||1.32||—||1.2|
|Serum phosphorus (normal range, 2.2–4.5), mg/dL||6.5||6.7||3.2|
|Serum PTH (normal range, 16.5–70), pg/mL
|Serum bicarbonate (normal range, 22–30), mg/dL||33||—||27|
|25-hydroxyvitamin D (normal range, 35–80), ng/mL||16.7||—||20|
|1,25-hydroxyvitamin D (normal range, 10–75), pg/mL||9||—||18.6|
|Urine calcium to creatinine ratio||0.149||—||0.01|
|Fractional excretion of phosphorus (FePO4)||5.20%||—||16%|
|Tubular reabsorption of phosphorus||94.70%||—||84.00%|
|FGF-23 level (normal range, 44–215 RU/mL)
|Serum albumin, serum magnesium, cortisol, and TSH levels
a PTH, parathyroid harmone.
b TMP/GFR, The ratio of tubular maximum reabsorption rate of phosphate to the glomerular filtration rate.
c FGF-23, Fibroblast Growth Factor-23.
d TsH, Thyroid stimulating Hormone.
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The authors have no financial or other conflicts of interest to disclose.
© 2014 Southern Society for Clinical Investigation. Published by Elsevier Inc. All rights reserved.