Standard treatment of hypoparathyroidism consists of supplementation of calcium and vitamin D analogues, which does not fully restore calcium homeostasis. In some patients, hypoparathyroidism is refractory to standard treatment with persistent low serum calcium levels and associated clinical complications. Here, we report on three patients (58-year-old male, 52-year-old female, and 48-year-old female) suffering from severe treatment-refractory postsurgical hypoparathyroidism. Two patients had persistent hypocalcemia despite oral treatment with up to 4 µg calcitriol and up to 4 g calcium per day necessitating additional i.v. administration of calcium gluconate 2–3 times per week, whereas the third patient presented with high frequencies of hypocalcemic and treatment-associated hypercalcemic episodes. S.c. administration of rhPTH (1–34) twice daily (40 µg/day) or rhPTH (1–84) (100 µg/day) only temporarily increased serum calcium levels but did not lead to long-term stabilization. In all three cases, treatment with rhPTH (1–34) as continuous s.c. infusion via insulin pump was initiated. Normalization of serum calcium and serum phosphate levels was observed within 1 week at daily 1–34 parathyroid hormone doses of 15 µg to 29.4 µg. Oral vitamin D and calcium treatment could be stopped or reduced and regular i.v. calcium administration was no more necessary. Ongoing efficacy of this treatment has been documented for up to 7 years so far. Therefore, we conclude that hypoparathyroidism that is refractory to both conventional treatment and s.c. parathyroid hormone (single or twice daily) may be successfully treated with continuous parathyroid hormone administration via insulin pump.
Standard treatment of hypoparathyroidism still consists of administration of calcium and active vitamin D.
Very few patients with hypoparathyroidism also do not respond sufficiently to standard treatment or administration of s.c. parathyroid hormone once or twice daily.
In those cases, continuous s.c. administration of parathyroid hormone via insulin pump may represent a successful treatment alternative.
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.
Clinicians prescribing ferric carboxymaltose (Ferinject®) should be aware of the common side effect of hypophosphataemia, which could be mild, moderate or severe.
Patients receiving iron infusion should be educated concerning this potential side effect.
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.
Patients may require phosphate and vitamin D replacement along with monitoring for a long period after iron infusion-induced hypophosphataemia.
Every incident should be reported to the designated body so that the true prevalence and management thereof can be ascertained.
Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is a rare, autosomal recessive disorder caused by mutations in the SLC34A3 gene that encodes the renal sodium-dependent phosphate cotransporter 2c (NaPi-IIc). It may present as intermittent mild hypercalcemia which may attract initial diagnostic attention but appreciation of concomitant hypophosphatemia is critical for consideration of the necessary diagnostic approach. A 21-year-old woman was assessed by adult endocrinology for low bone mass. She initially presented age two with short stature, nephrocalcinosis and mild intermittent hypercalcemia with hypercalciuria. She had no evidence of medullary sponge kidney or Fanconi syndrome and no bone deformities, pain or fractures. She had recurrent episodes of nephrolithiasis. In childhood, she was treated with hydrochlorothiazide to reduce urinary calcium. Upon review of prior investigations, she had persistent hypophosphatemia with phosphaturia, low PTH and a high-normal calcitriol. A diagnosis of HHRH was suspected and genetic testing confirmed a homozygous c.1483G>A (p.G495R) missense mutation of the SLC34A3 gene. She was started on oral phosphate replacement which normalized her serum phosphate, serum calcium and urine calcium levels over the subsequent 5 years. HHRH is an autosomal recessive condition that causes decreased renal reabsorption of phosphate, leading to hyperphosphaturia, hypophosphatemia and PTH-independent hypercalcemia due to the physiologic increase in calcitriol which also promotes hypercalciuria. Classically, patients present in childhood with bone pain, vitamin D-independent rickets and growth delay. This case of a SLC34A3 mutation illustrates the importance of investigating chronic hypophosphatemia even in the presence of other more common electrolyte abnormalities.
Hypophosphatemia is an important diagnostic clue that should not be ignored, even in the face of more common electrolyte disorders.
HHRH is a cause of PTH-independent hypophosphatemia that may also show hypercalcemia.
HHRH is a cause of hypophosphatemic nephrocalcinosis that should not be treated with calcitriol, unlike other congenital phosphate wasting syndromes.
Some congenital phosphate wasting disorders may not present until adolescence or early adulthood.
HNF4A gene mutations have been reported in cases of transient and persistent hyperinsulinaemic hypoglycaemia of infancy (HHI), particularly in families with adulthood diabetes. The case of a patient with HHI, liver impairment and renal tubulopathy due to a mutation in HNF4A is reported.
Urine specimen study in cases of HHI with diazoxide response is necessary to rule out specific metabolic conditions (l-3-hydroxyacyl-coenzyme A dehydrogenase deficiency) or tubular renal involvement.
Hyperinsulinaemic hypoglycaemia due to the heterozygous mutation (p.Arg63Trp, c. 187C > T) in the HNF4A gene is associated with renal tubulopathy and liver involvement.
Follow-up of patients diagnosed of HHI is mandatory to detect associated conditions.
Maria P YavropoulouDivision of Clinical and Molecular Endocrinology, 1st Department of Internal Medicine, AHEPA University Hospital, Aristotle University of Thessaloniki, 1 Stilponos, Kyriakidi Street, Thessaloniki, 54636, Greece
Nikolina GerothanasiDivision of Clinical and Molecular Endocrinology, 1st Department of Internal Medicine, AHEPA University Hospital, Aristotle University of Thessaloniki, 1 Stilponos, Kyriakidi Street, Thessaloniki, 54636, Greece
Athanasios FrydasDivision of Clinical and Molecular Endocrinology, 1st Department of Internal Medicine, AHEPA University Hospital, Aristotle University of Thessaloniki, 1 Stilponos, Kyriakidi Street, Thessaloniki, 54636, Greece
Evangelia TriantafyllouDivision of Clinical and Molecular Endocrinology, 1st Department of Internal Medicine, AHEPA University Hospital, Aristotle University of Thessaloniki, 1 Stilponos, Kyriakidi Street, Thessaloniki, 54636, Greece
John G YovosDivision of Clinical and Molecular Endocrinology, 1st Department of Internal Medicine, AHEPA University Hospital, Aristotle University of Thessaloniki, 1 Stilponos, Kyriakidi Street, Thessaloniki, 54636, Greece
Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused primarily by benign mesenchymal tumors. These tumors typically follow a benign clinical course and local recurrence occurs in <5% of cases. We investigated a 49-year-old man with a recurrent mesenchymal phosphaturic tumor showing no signs of malignancy. The patient suffered from chronic muscle weakness, myalgia and cramps. His medical record included the diagnosis of oncogenic osteomalacia, for which he was submitted to tumor resection in the left leg three times before. Laboratory examination showed hypophosphatemia, hyperphosphaturia and an elevated serum FGF23 level. A radical surgical approach (amputation) was advised, however, complete biochemical and clinical remission was not reached. Molecular analysis of the tumor cells demonstrated overexpression of growth factor receptors implicated in tumor angiogenesis and metastatic potential (platelet derived growth factor type A (PDGFRA), PDGFRB and vascular endothelial growth factor receptor) together with increased expression of FGF23, x-linked-phosphate-regulating endopeptidase and KLOTHO. TIO is usually associated with benign phosphauturic tumors and, when identified, resection of the tumor leads to complete remission in the majority of cases. The underlying pathophysiology of recurrences in these tumors is not known. This is the first report showing increased expression of growth factor receptors in a locally aggressive but histopathologically benign phosphaturic mesenchymal tumor.
TIO is usually associated with benign soft tissue or bone neoplasms of mesenchymal origin.
These tumors typically follow a benign clinical course and even in the rare malignant cases local recurrence occurs in <5%.
Successful identification and removal of the tumor leads to full recovery in the majority of cases.