Fibroblast Growth Factor 23-Producing Phosphaturic Mesenchymal Tumor with Extraordinary Morphology Causing Oncogenic Osteomalacia

A possible cause of hypophosphatemia is paraneoplastic secretion of fibroblast growth factor 23 (FGF-23). Tumors secreting FGF-23 are rare, mostly of mesenchymal origin, usually benign, and may be located anywhere in the body, including hands and feet, which are often not represented in conventional imaging. A 50-year-old woman presented with diffuse musculoskeletal pain and several fractures. Secondary causes of osteoporosis were excluded. Laboratory analysis revealed hypophosphatemia and elevated alkaline phosphatase, parathyroid hormone, and FGF-23. Thus, oncogenic osteomalacia due to neoplastic FGF-23 secretion was suspected. FDG-PET-CT and DOTATATE-PET-CT imaging demonstrated no tumor. Cranial MRI revealed a tumorous mass in the left cellulae ethmoidales. The tumor was resected and histopathological examination showed a cell-rich tumor with round to ovoid nuclei, sparse cytoplasm, and sparse matrix, resembling an olfactory neuroblastoma. Immunohistochemical analysis first led to diagnosis of olfactory neuroblastoma, which was later revised to phosphaturic mesenchymal tumor. Following the resection, FGF-23 and phosphate levels normalized. In conclusion, we here describe a patient with an FGF-23-secreting phosphaturic mesenchymal tumor with an unusual morphology. Furthermore, we emphasize diagnostic pitfalls when dealing with FGF-23-induced hypophosphatemia.

The Association of Hypophosphatemia With Resistant Lactic Acidosis in Critical Care Illness

Critically ill patients are known to have a variety of electrolyte abnormalities. Lactic acidosis can frequently be seen secondary to shock states and is usually treated with aggressive volume resuscitation. Interestingly, hypophosphatemia is a potential cause of resistant lactic acidosis, which may not be as commonly identified or considered. We present a case of a 42-year-old man admitted twice over a span of 6 months with an elevated lactate level that did not resolve with volume resuscitation. It was ultimately determined that his lactic acidosis was due to hypophosphatemia after ruling out other potential causes. Phosphate replacement therapy resulted in the normalization of his lactate. In the literature, multiple theories have indicated the association of hypophosphatemia with lactic acidosis though no prior cases exist supporting a direct relationship. In this case, we set forth to evaluate the complicated relationship between all of these factors and to highlight the importance of early detection and treatment of hypophosphatemia, which may be beneficial in treating lactic acidosis.

Elevated FGF23 in a patient with hypophosphatemic osteomalacia associated with neurofibromatosis type 1

CONTEXT

The mechanism behind hypophosphatemia in the setting of neurofibromatosis type 1 (NF1) is not known. We describe a possible role of fibroblast growth factor-23 (FGF23) in the pathophysiology of hypophosphatemia in a patient with NF1.

CASE DESCRIPTION

A 34-year woman with NF1 presented with severe hypophosphatemia, osteomalacia, and elevated plasma FGF23. The patient had considerable improvement on replacement of oral phosphate. Two Ga68 DOTANOC PET-CT scans over a period of 2 years failed to detect any localized uptake. Immuno-staining for FGF23 was absent in the neural-derived tumour cells of the neurofibromas in the proband.

CONCLUSION

The patient with NF1 had elevated circulating FGF23. Tumour cells in the neurofibroma tissues did not stain for FGF23 on IHC. It is unlikely for neurofibromas to contribute to high circulating FGF23 levels in the proband.

Refeeding Syndrome

Refeeding syndrome describes the metabolic disturbances and clinical sequelae that occur in response to nutritional rehabilitation of patients who are moderate to severely malnourished. When risk factors are not identified and nutrition therapy is not managed appropriately, devastating consequences such as electrolyte depletion and imbalances, fluid overload, arrhythmia, seizure, encephalopathy, and death may occur. As this entity is often unrecognized, especially in pediatrics, becoming familiar with the pathophysiology, clinical manifestations, and management strategies will help clinicians caring for children avoid unnecessary morbidity and mortality. [Pediatr Ann. 2019;48(11):e448-e454.].

Reliability of calcium-phosphorus (Ca/P) ratio as a new, accurate and inexpensive tool in the diagnosis of some Ca-P disorders

PURPOSE

The serum calcium/phosphorus (Ca/P) ratio is an accurate tool to differentiate patients with primary hyperparathyroidism (PHPT) from healthy subjects. However, other disorders of the Ca-P metabolism might impair the Ca/P ratio, such as hypophosphatemia (HypoP) not PHPT related. The aim of this study is to examine the diagnostic value of Ca/P ratio in the diagnosis of PHPT and HypoP not PHPT related.

METHODS

Single-center, retrospective, case-control study, including 150 patients with PHPT and 306 patients with HypoP, compared with 150 controls. HypoP patients were enrolled among HIV-infected patients by selecting those with Fanconi-like syndrome due to antiretroviral treatment. Parameters which were measured were serum Ca, P, parathyroid hormone (PTH), 25-OH vitamin D, albumin and creatinine).

RESULTS

The Ca/P ratio was significantly higher in PHPT and HypoP patients, compared to controls (p < 0.0001). At receiver operator characteristic (ROC) curve analysis, the cut-off of 3.56 (2.75 SI) for Ca/P ratio was able to identify patients with PHPT and HypoP (sensitivity 95%; specificity 93%). Among patients with Ca/P ratio above 3.56, the thresholds of 10.3 mg/dL (2.6 mmol/L) for serum Ca (sensitivity 93%; specificity 98%) and 80.5 pg/mL for PTH (sensitivity 91%; specificity 91%) were defined for the specific diagnosis of PHPT.

CONCLUSIONS

The Ca/P ratio above 3.56 (2.75 SI) is a highly accurate tool to identify PHPT and HypoP not PHPT-related patients. Thanks to its simplicity, this index can be proposed as a screening and first-line examination in the diagnostic work-up when a disorder of Ca-P metabolism is suspected or should be ruled out.

Sinonasal hemangiopericytoma caused hypophosphatemic osteomalacia: A case report

RATIONALE

Tumor-induced osteomalacia (TIO) is a rare, paraneoplastic syndrome featured with fibroblast growth factor 23 (FGF23) secretion primarily by benign mesenchymal tumors and sometimes by malignancies. TIO diagnosis and treatment is often delayed because TIO usually has nonspecific generalized bone pain and weakness, and location of TIO tumor is quite challenging. Very few TIO caused by sinonasal hemangiopericytoma have been reported in the literature.

PATIENT CONCERNS

A 40-year-old Chinese woman presented with diffuse bone pain for more than 1 year. Laboratory examination showed hypophosphatemia, hyperphosphaturia, hypocalcemia, an elevated serum alkaline phosphatase (ALP) level and bone-specific ALP level. Imaging studies revealed low bone mineral density (BMD) and multiple pseudofractures at the ribs. F-18 fluorodeoxyglucose positron emission tomography was negative in searching for tumors. Because no tumor was located, the patient was treated with oral phosphate, calcium, and alfacalcidol, and achieved great relief in her symptoms and improvement in BMD. Six years later, the patient had breast cancer surgery and received chemotherapy, and still had hypophosphatemia. During this time, nasopharyngo-fiberscope showed nasal mass in her left nasal cavity. Then she had her nasal polyps removed and surprisingly the serum phosphate became normal.

DIAGNOSES AND INTERVENTIONS

The patient had the nasal mass resected, and pathological diagnosis of the nasal mass was sinonasal hemangiopericytoma. Immunohistochemical analysis was positive for FGF23. Thus the final diagnosis was osteomalacia induced by sinonasal hemangiopericytoma. Phosphate supplementation and alfacalcidol were discontinued.

OUTCOMES

The patient had normal serum phosphate after 6-month follow-up.

LESSONS

By presenting this case, we hope to remind clinicians that in patients with osteomalacia with undetermined reason and intranasal polypoid mass, sinonasal hemangiopericytoma should be suspected.

Legionella Pneumonia Complicated with Acquired Fanconi Syndrome

Legionella pneumonia is occasionally accompanied by renal complications; however, the cause of this remains unknown. We herein report a 70-year-old Japanese man with Legionella pneumonia who presented with hyponatremia, hypophosphatemia, and hypouricemia. The levels of urinary β2-microglobulin and N-acetyl-β-D-glucosaminidase were remarkably high, indicating severe renal tubular damage. The presence of glycosuria and aminoaciduria as well as increased fractional excretion of uric acid and decreased tubular reabsorption of phosphate indicated that the patient's condition was complicated with Fanconi syndrome. After antimicrobial therapy, the electrolyte abnormalities and renal tubular damage were completely resolved.

The Relationship between Hypomagnesemia and Pulmonary Function Tests in Patients with Chronic Asthma

OBJECTIVE

To investigate the relationship between serum values of magnesium and the parameters of the pulmonary function tests (PFT) in patients with chronic asthma.

SUBJECTS AND METHODS

This study recruited 50 patients with chronic stable asthma and 40 healthy individuals as a control group. Data on age, sex, severity of asthma, PFT, and details of drug therapy were obtained from each group. Serum magnesium, potassium, phosphorus, calcium, and sodium levels were also measured. To evaluate differences between groups, the Student t test or Mann-Whitney U test was performed for continuous variables, and the χ2 test for categorical variables.

RESULTS

In the asthma group, 10% (n = 9) of the patients had hypomagnesemia and 5.5% (n = 5) had hypophosphatemia. Patients with asthma were divided into two groups: the hypomagnesemic group (n = 9) and the normomagnesemic group (n = 41). Forced expiratory volume in 1 s (FEV1), FEV1%, peak expiratory flow (PEF), and PEF% were lower in the hypomagnesemic group than in the normomagnesemic group (p = 0.02). Multiple logistic regression analysis revealed a statistically significant association between hypomagnesemia and PFT in the hypomagnesemic asthmatic group. The correlations of age with FEV1, FEV1%, PEF, and PEF% were as follows: p = 0.00, r = 0.29; p = 0.00, r = 0.43; p = 0.03, r = 0.22; p = 0.00, r = 0.38; and p = 0.03, r = 0.22, respectively. The correlation of serum magnesium levels with PFT (FEV1, FEV1%, PEF, PEF%) were as follows: p = 0.001, r = 0.29; p = 0.001, r = 0.43; p = 0.03, r = 0.22; and p = 0.001, r = 0.38, respectively. The other electrolytes were within the normal range in both groups.

CONCLUSION

In this study, hypomagnesemia and hypophosphatemia were found to be the most common electrolyte abnormalities in patients with chronic stable asthma. FEV1, FEV1%, PEF, and PEF% were significantly lower in asthmatic patients with hypomagnesemia compared to asthmatic patients with normomagnesemia.

Bone Histology of Two Cases with Osteomalacia Related to Low-dose Adefovir

We performed a bone histomorphometric analysis in two patients demonstrating Fanconi syndrome with hypophosphatemia, adefovir-related bone disease and chronic hepatitis B infection. Both patients had osteomalacia, but showed two different histological patterns. The osteoid volume of the patient without risedronate increased with [(osteoid volume/ bone volume)×100=18.6%]. However, the osteoid volume of the patient receiving risedronate without vitamin D analogue showed a greater increase of 53.8%. In both patients bone pain and hypophosphatemia subsided soon after the discontinuation of adefovir and the administration of phosphate derivative. These findings show that bisphosphonate may worsen this disease when this drug is administered without a vitamin D analogue.

[Limited evidence for monitoring and treatment of hypophosphataemia in critically ill patients]

Hypophosphataemia is a potentially hazardous metabolic disturbance which is common in critically ill patients. The condition is reported to be associated with severe complications and increased mortality. It is unknown, whether hypophosphataemia has a causal effect or reflects the severity of illness. There are no randomized clinical trials to support treatment of hypophosphataemia with intravenous phosphate substitution, which has resulted in large variations in monitoring and treatment of hypophosphataemia in the intensive care unit.

A 'shocking' finish to the Dam tot Damloop event

A patient with status epilepticus after long-distance running is described. The patient, a young woman, was brought to our hospital with status epilepticus after completing in a running event, probably caused by an extremely low phosphate level of 0.30 mmol/l. Hypophosphataemia is a rare complication of running and can be caused by the use of phosphate in the glycogenolyticand glycolytic pathway.

Rhabdomyolysis Due to Severe Hypophosphatemia in Diabetic Ketoacidosis

Rhabdomyolysis is a syndrome characterized by injury to skeletal muscle fibers with disruption and release of toxic metabolites into circulation. It is characterized by triad of muscle weakness, myalgia and dark urine and is associated with increased creatine kinase and lactate dehydrogenase. A severely malnourished 10 year old girl with severe diabetic ketoacidosis as hemr initial presentation of type 1 diabetes mellitus developed rhabdomyolysis (CK- 12,000 U/L) with non-oliguric renal failure during her initial course of hospital stay. The possible cause of her RM was attributed to severe hypophosphatemia (minimum serum phosphate, 0.8 mg/dL). Management of diabetic ketoacidosis phosphate supplementation and urinary alkalinization with diuresis improved her clinical course. She was discharged on Day 9 with Insulin. We recommend frequent monitoring of serum phosphate during early period of DKA, particularly in malnourished children, and its normalization in case of severe hypophosphatemia.

[Management of hypophosphatemia: a case report]

Hypophosphatemia is defined by a serum phosphate level lower than 0.8 mmol/l. If hypophosphatemia is chronically maintained, it is associated with muscular, osteous, neurological or cardio-respiratory disorders. We describe a patient with isolated hypophosphatemia, detail the mechanisms of phosphate homeostasis, and envisage the differential diagnosis of hypophosphatemia. Furthermore, we propose a sequential decisional algorithm based on basic biological tests and few complementary investigations. Treatment options are reviewed.

[The clinical characteristics of 26 cases of hypophosphatemia osteomalacia misdiagnosed as spondyloarthritis]

OBJECTIVE

To study and summarize the clinical features of hypophosphatemia osteomalacia (HO) misdiagnosed as spondyloarthritis (SpA), aiming to analyze the reasons of misdiagnosis and improve the prognosis of such patients.

METHODS

A total of 26 cases of HO misdiagnosed as SpA were selected. Clinical features, laboratory tests, and image presentations were analyzed. Related literatures were reviewed.

RESULTS

(1) Clinical characters: 26 patients were included (12 males and 14 females) with a median age of 38 years (range 20-60). The mean disease duration was 3.2 years (range 0.75 to 10 years). Of all the patients, 15 were diagnosed as tumor-induced HO, 4 were long-term oral adefovir dipivoxil-related HO, 3 were associated with Fanconi syndrome, 2 were related to hyperparathyroidism, while 2 were Sjogren's syndrome complicated with renal tubular acidosis. All of the 26 patients presented with low back pain including 15 with night pain. The time of morning stiffness was about 30 minutes. Non-steroidal anti-inflammatory drugs were given to each patient whereas with poor efficacy, neither did other agents work well, such as glucocorticoids, disease modifying anti-rheumatic drugs and biologics. (2) LABORATORY FINDINGS: the platelet count and inflammatory markers such as erythrocyte sedimentation rate, C-reactive protein (CRP) were usually normal. The level of serum calcium was normal or slightly lower, nevertheless, all patients had hypophosphatemia and increased level of alkaline phosphatase (ALP). Patients with adefovir dipivoxil-related HO, Fanconi syndrome or Sjogren's syndrome complicated with renal tubular acidosis were characterized by hypokalemia, hyperchloremia and alkaline urine. Patients with hyperparathyroidism had elevated parathyroid hormone (PTH). Positive antinuclear antibodies (ANA) (titer ≥ 1: 320), anti-SSA/SSB antibodies were found in patients with Sjogren's syndrome. (3) Radiographic features: sacroiliac joint lesions were found in X-ray, CT, positron emission tomography (PET-CT) or MRI, however the lesions in sacrum or ilium were predominant rather than in joints. Abnormal bone imaging in ribs, long bones and soft tissues in addition to joints could be detected by bone scintigraphy.

CONCLUSION

HO is not uncommon in daily practice. Besides SpA, other diseases should be considered in the setting of low-back pain and diseased sacroiliac joints. Comprehensive screening of bone metabolic parameters contributes to the timely diagnosis of HO.

Hypophosphatemic osteomalacia and bone sclerosis caused by a novel homozygous mutation of the FAM20C gene in an elderly man with a mild variant of Raine syndrome

BACKGROUND

Hypophosphatemia and increased serum fibroblast growth factor 23 (FGF23) levels have been reported in young brothers with compound heterozygous mutations for the FAM20C gene; however, rickets was not observed in these cases. We report an adult case of Raine syndrome accompanying hypophosphatemic osteomalacia with a homozygous FAM20C mutation (R408W) associated with increased periosteal bone formation in the long bones and an increase in bone mineral density in the femoral neck.

CASE

The patient, a 61-year-old man, was born from a cousin-to-cousin marriage. A short stature and severe dental demineralization were reported at an elementary school age. Hypophosphatemia was noted inadvertently at 27years old, at which time he started to take an active vitamin D metabolite (alphacalcidol) and phosphate. He also manifested ossification of the posterior longitudinal ligament. On bone biopsy performed at the age of 41years, we found severe osteomalacia surrounding osteocytes, which appeared to be an advanced form of periosteocytic hypomineralized lesions compared to those reported in patients with X-linked hypophosphatemic rickets. Laboratory data at 61years of age revealed markedly increased serum intact-FGF23 levels, which were likely to be the cause of hypophosphatemia and the decreased level of 1,25(OH)2D. We recently identified a homozygous FAM20C mutation, which was R408W, in this patient. When expressed in HEK293 cells, the R408W mutant protein exhibited impaired kinase activity and secretion.

DISCUSSION

Our findings suggest that certain homozygous FAM20C mutations can cause FGF23-related hypophosphatemic osteomalacia and indicate the multiple roles of FAM20C in bone.

Fibroblast growth factor 23 is elevated in tenofovir-related hypophosphatemia

In human immunodeficiency virus (HIV)-infected patients, tenofovir disoproxil fumarate (TDF) may cause hypophosphatemia leading to osteomalacia due to renal phosphate wasting. Fibroblast growth factor 23 (FGF23) may play a role in this setting. We present an HIV-infected patient with TDF-induced profound hypophosphatemia, Fanconi syndrome, osteomalacia, and bilateral hip fracture. Routine serum biochemistry was assessed by standard methods. The plasma FGF23 concentration was measured at Mayo Laboratories (Scottsdale, AZ, USA). Bone mineral density (BMD) was measured using a Hologic Discovery densitometer. At presentation, the patient's plasma C-terminal FGF23 was 2,760 reference units (RU)/mL (15 times upper limit of normal; reference interval [RI] ≤ 180 RU/mL), serum phosphate was 0.58 (RI 0.8-1.6 mmol/L), and TmPO4/GFR was 95%. DXA at the lumbar spine showed a Z score of -4.0. Vitamin D3 and oral phosphate were administered, and TDF was discontinued. After 4 months off TDF, lumbar spine BMD significantly increased by 12% (Z score -3.5); by 6 months the plasma C-terminal FGF23 declined to 1.8 times the upper limit of normal, and both urine and serum phosphate levels normalized. By its marked elevation and subsequent near normalization, FGF23 may be responsible for a component of the phosphate wasting syndrome in these patients. The time course of resolution was 6 months. As expected, with calcium, vitamin D, and phosphate management, BMD significantly improved with resolution of osteomalacia. Clinicians should be aware of this side effect of TDF and the time course of its resolution.

Rickets

Rickets, historically referred to as "the English disease", is common worldwide. Absence of phosphate at the growth plate and mineralising bone surfaces due to inadequate vitamin D supply either from sunlight exposure or diet is the main cause. Inherited disorders causing hypophosphataemia have shown the intricacies of phosphate metabolism. Present advice about the provision of vitamin D to young infants needs to be clarified; the existing guidance is fragmentary and contradictory, and will not help to eradicate the disease.

Postzygotic HRAS mutation causing both keratinocytic epidermal nevus and thymoma and associated with bone dysplasia and hypophosphatemia due to elevated FGF23

INTRODUCTION

Epidermal nevus syndrome is a rare group of disorders characterized by the combination of congenital epidermal nevi and extracutaneous features, including skeletal, neurological, ocular, and other systemic findings. We report a case of keratinocytic epidermal nevus syndrome that includes a thymoma, bone dysplasia, and hypophosphatemia with elevated fibroblast growth factor 23 (FGF23) levels associated with postzygotic HRAS mutation.

CASE REPORT

A 14-year-old boy was admitted due to recent limping. The physical examination revealed multiple right-sided linear epidermal nevi along Blaschko's lines. Magnetic resonance imaging showed cystic lesions in cervical bones and thymoma, and x-ray examination showed cystic lesions in the hands. Biochemical studies demonstrated severe hypophosphatemia, normocalcemia, high normal PTH, low 25-hydroxyvitamin D and low 1,25-dihydroxyvitamin D levels. The serum FGF23 C-terminal level was normal, but the intact FGF23 level was found to be elevated. Genetic evaluation revealed a heterozygote mutation in the HRAS gene in both the keratinocytic epidermal nevus and thymoma but not in DNA extracted from blood lymphocytes, thus establishing the mutation as postzygotic.

DISCUSSION

Postzygotic mutations in HRAS lead to elevation of FGF23 levels, as found in mutated PHEX, FGF23, DMP1, and ENPP1 genes, which lead to hypophosphatemia.

CONCLUSION

An identical postzygotic HRAS mutation was shown to be present in both keratinocytic epidermal nevus and thymoma and to be associated with bone lesions and hypophosphatemia due to elevated FGF23 levels. These may all be related to the HRAS mutation.

Severe hypophosphataemia after intravenous iron administration

Currently, in many centres, intravenous administration of iron is becoming increasingly popular because of higher efficacy and decreased side effects, mainly gastrointestinal, compared with oral iron therapy. Studies of intravenous ferric carboxymaltose administration in the postpartum setting and in patients with non-dialysis-dependent chronic kidney disease revealed a decrease in serum phosphate levels that was generally asymptomatic and transient. Here, we report four cases of severe and symptomatic hypophosphataemia after intravenous iron administration. All patients received this as therapy for iron deficiency anaemia due to heavy menstrual bleeding. In most cases, a pre-existent disorder in the phosphate homeostasis existed, such as a secondary (cases 3 and 4) or tertiary hyperparathyroidism (case 1). However, in the second case there were no risk factors for a dysregulation of the phosphate homeostasis. Based on these findings, we conclude that severe and symptomatic hypophosphatemia can occur as a side effect of intravenous iron administration and can persist for months after administration. Especially patients with low phosphate levels prior to therapy due to concomitant disorders in phosphate homeostasis (e.g. hyperparathyroidism, vitamin D deficiency) are at risk.

Prolonged disturbance of consciousness caused by severe hypophosphatemia: a report of two cases

We herein describe two patients with a prolonged disturbance of consciousness due to severe hypophosphatemia. Case one presented with pneumococcal infection and acute exacerbation of chronic obstructive pulmonary disease and asthma. Case two presented with diabetic foot infections and diabetic ketoacidosis. Both patients responded to initial therapy for their primary diseases, but consciousness became worse in both cases. Their test results for impaired consciousness revealed severe hypophosphatemia; therefore, phosphate replacement therapy was administered, thus resulting in complete alertness. These cases demonstrate that we should consider the possibility of hypophosphatemia in critically ill patients with an altered consciousness.