Diagnosis and Treatment > Signs and Symptoms > Renal phosphate wasting (isolated)
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Summary
Iron (ferric carboxymaltose) infusion therapy is used to treat severe iron deficiency which is not responding to the first-line oral iron therapy. However, it can also cause severe renal wasting of phosphate resulting in severe hypophosphataemia in some patients. Despite the growing number of case reports, this side effect is not well known to healthcare professionals. The product labelling information sheet does mention that hypophosphataemia can be a side effect, but also says that this side effect is usually transient and asymptomatic. We report a challenging case of a patient who developed severe, symptomatic and prolonged hypophosphataemia after an intravenous iron infusion for severe iron deficiency.
Learning points:
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Clinicians prescribing ferric carboxymaltose (Ferinject®) should be aware of the common side effect of hypophosphataemia, which could be mild, moderate or severe.
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Patients receiving iron infusion should be educated concerning this potential side effect.
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Pre-existing vitamin D deficiency, low calcium levels, low phosphate levels or raised parathyroid hormone levels may be risk factors, and these should be evaluated and corrected before administering intravenous iron.
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Patients may require phosphate and vitamin D replacement along with monitoring for a long period after iron infusion-induced hypophosphataemia.
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Every incident should be reported to the designated body so that the true prevalence and management thereof can be ascertained.
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Summary
Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by renal phosphate wasting leading to hypophosphatemia due to excessive actions of fibroblast growth factor 23 (FGF23) produced by the tumors. Although the best way of curing TIO is complete resection, it is usually difficult to detect the culprit tumors by general radiological modalities owing to the size and location of the tumors. We report a case of TIO in which the identification of the tumor by conventional imaging studies was difficult. Nonetheless, a diagnosis was made possible by effective use of multiple modalities. We initially suspected that the tumor existed in the right dorsal aspect of the scapula by 68Ga-DOTATOC positron emission tomography/computed tomography (68Ga-DOTATOC-PET/CT) and supported the result by systemic venous sampling (SVS). The tumor could also be visualized by 3T-magnetic resonance imaging (MRI), although it was not detected by 1.5T-MRI, and eventually be resected completely. In cases of TIO, a stepwise approach of 68Ga-DOTATOC-PET/CT, SVS and 3T-MRI can be effective for confirmation of diagnosis.
Learning points:
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TIO shows impaired bone metabolism due to excessive actions of FGF23 produced by the tumor. The causative tumors are seldom detected by physical examinations and conventional radiological modalities.
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In TIO cases, in which the localization of the culprit tumors is difficult, 68Ga-DOTATOC-PET/CT should be performed as a screening of localization and thereafter SVS should be conducted to support the result of the somatostatin receptor (SSTR) imaging leading to increased diagnosability.
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When the culprit tumors cannot be visualized by conventional imaging studies, using high-field MRI at 3T and comparing it to the opposite side are useful after the tumor site was determined.
