Tumor-induced osteomalacia

Tumour-induced osteomalacia: the long road to diagnosis and recovery

Tumour-induced osteomalacia is caused by tumorous production of fibroblast growth factor 23 (FGF23) leading to urinary phosphate wasting, hypophosphataemia and decreased vitamin D activation. The resulting osteomalacia presents with muscle weakness and bone pain but progresses to multiple pathological fractures. Patients often remain undiagnosed for years with severe physical, psychological and economic ramifications. A young woman presented with multiple spontaneous fractures including bilateral femoral fractures. Laboratory tests revealed severe hypophosphataemia, elevated bone turnover markers and low to normal calcium and 25-hydroxy-vitamin D levels. Treatment with phosphate, alfalcalcidol, calcium and magnesium was initiated. 68Gallium-DOTATOC positron emission tomography imaging revealed a mass in the right foot and venous sampling of FGF23 from all extremities confirmed this tumour as the culprit. Biopsy and histology were consistent with a phosphaturic mesenchymal tumour, which was surgically resected. Phosphate levels quickly normalised postoperatively but a long convalescence with hungry bone syndrome, fracture healing and physical therapy followed.

Preoperative evaluation and orthopedic surgical strategies for tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO), also known as oncogenic osteomalacia, is very rare, with about 1000 reported cases globally. Removing most TIO culprit tumors requires the evaluation and intervention of orthopedic doctors. However, orthopedic doctors often have a poor understanding of the optical treatment of TIO due to its rarity. In addition, most TIO patients lack specific clinical manifestations. Also, the clinical localization and qualitative diagnosis of TIO are difficult and thus can easily be misdiagnosed and mistreated. Furthermore, the true incidence rate of TIO may be underestimated. Although many breakthroughs have been made in exploring the pathogenesis, clinical diagnosis, and treatment of TIO, rational and standardized orthopedic surgical treatment experience summary and sorting for TIO patients are lacking. In this article, the recent experience and progress in the field of orthopedic surgical treatment for TIO globally have been summarized, providing a theoretical basis and new clinical practice guidance for the rational treatment of TIO patients.

Spectrum of PHEX Mutations and FGF23 Profiles in a Taiwanese Cohort With X-Linked Hypophosphatemia Including 102 Patients

BACKGROUND/AIM

X-linked hypophosphatemia (XLH), the most common form of hereditary rickets, results from loss-of-function mutations in the phosphate-regulating PHEX gene. Elevated fibroblast growth factor 23 (FGF23) contributes to hypophosphatemia in XLH. This study aimed to characterize PHEX variants and serum FGF23 profiles in Taiwanese patients with XLH.

PATIENTS AND METHODS

We retrospectively reviewed the records of 102 patients clinically suspected of having hypophosphatemic rickets from 2006 to 2022. Serum intact Fibroblast growth factor-23 (iFGF23) levels were measured on clinic visit days. PHEX mutations were identified using Sanger sequencing, and negative cases were analyzed using whole-exome sequencing.

RESULTS

The majority (92.1%) of patients exhibited elevated FGF23 compared with normal individuals. Among 102 patients, 44 distinct PHEX mutations were identified. Several mutations recurred in multiple unrelated Taiwanese families. We discovered a high frequency of novel PHEX mutations and identified variants associated with extreme FGF23 elevation and tumorigenesis.

CONCLUSION

Our findings revealed the PHEX genotypic variants and FGF23 levels in Taiwanese patients with XLH. These results are crucial given the recent approval of burosumab, a monoclonal FGF23 antibody, for XLH therapy. This study provides key insights into the clinical management of XLH in Taiwan.

A case of hyperparathyroidism secondary to tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome in which tumor-induced osteochondrosis is a metabolic bone disease caused by increased renal excretion of phosphorus due to excessive secretion of fibroblast growth factor 23 (FGF23) by tumor tissue. We report here a rare case of TIO in which the tumor was found in the hyoid body and the patient had tertiary hyperparathyroidism. The patient's symptoms did not improve after removal of the tumor from the hyoid body, and the patient's hypophosphatemia was gradually improved after subsequent removal of the left parathyroid gland. TIO derived from the tongue tumor is very rare, and also subsequent tertiary hyperparathyroidism is even rarer. This report helps to improve the understanding of TIO and provides reference in the diagnosis and treatment of TIO.

Burosumab Improves Patient-Reported Outcomes in Adults With Tumor-Induced Osteomalacia: Mixed-Methods Analysis

Tumor-induced osteomalacia (TIO) is an ultra-rare disease caused by tumors that secrete fibroblast growth factor 23, leading to chronic hypophosphatemia, poor skeletal health, and impaired physical function. In a phase 2 trial (UX023T-CL201; NCT02304367; n = 14), 48 weeks of burosumab treatment restored phosphate homeostasis, with improvements in skeletal health, functional mobility, and patient-reported pain, fatigue, and health-related quality of life (HRQL) (SF-36 v2). Here, we report an exploratory mixed-methods analysis of change from baseline after 144 weeks of burosumab treatment alongside qualitative data from exit interviews with 8 of 14 trial participants to evaluate meaningful treatment effects from a patient perspective. The interview subset (n = 8) reported pain and fatigue and compromised HRQL at baseline. In the interviews, participants reported that compromised HRQL and pain were the most important aspects of the disease to treat; both were considered more bothersome than fatigue and compromised physical function and activities of daily living. Improvements in pain and fatigue after treatment were reported, some of which achieved statistically and/or clinically meaningful thresholds. Furthermore, improvements in SF-36 v2 scores were most pronounced in the Physical Component Score and its Physical Function and Bodily Pain domains. Overall, the interview subset provided descriptions of symptomatic improvement and its clinical meaningfulness, including physical function, participation in activities of daily living, and mental well-being. Thus, this exploratory mixed-methods analysis provides deeper understanding of patients' perception of clinical meaningfulness beyond that articulated in validated patient-reported outcome instruments. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Hypophosphatemia in Patients With Multiple Myeloma

Hypophosphatemia is among the most common electrolyte abnormalities, especially among patients with underlying malignancies, and is frequently associated with adverse prognoses. Phosphorus levels are regulated through a number of mechanisms, including parathyroid hormone (PTH), fibroblast growth factor-23 (FGF-23), vitamin D, and other electrolyte levels themselves. Clinically, the findings are nonspecific, and the diagnosis is frequently delayed. This article is a narrative literature review. The PubMed database was searched for relevant articles pertaining to hypophosphatemia causes and consequences in patients suffering from multiple myeloma. We found a variety of causes of hypophosphatemia in patients with multiple myeloma. Tumor-induced osteopenia, although more common among patients with small squamous cell carcinomas, can occur with multiple myeloma as well. Additionally, both light chains themselves and medications can trigger Fanconi syndrome, which leads to phosphorus wasting by the kidney. Bisphosphonates, in addition to being a possible cause of Fanconi syndrome, lead to a decrease in calcium levels, which then stimulates parathyroid hormone (PTH) release, predisposing the patient to significant hypophosphatemia. Additionally, many of the more modern medications used to manage multiple myeloma have been associated with hypophosphatemia. A better understanding of those mechanisms may give clinicians a clearer idea of which patients may need more frequent screening as well as what the potential triggers in the individual patient may be.

Global guidance for the recognition, diagnosis, and management of tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by mesenchymal tumors that secrete fibroblast growth factor 23 (FGF23). Patients present with progressive bone pain, muscle weakness, and fragility fractures. TIO is characterized by hypophosphatemia, excess renal phosphate excretion, and low/inappropriately normal 1,25-dihydroxyvitamin D (1,25(OH)₂ D) levels. Rarity and enigmatic clinical presentation of TIO contribute to limited awareness among the medical community. Accordingly, appropriate diagnostic tests may not be requested, leading to delayed diagnosis and poorer patient outcomes. We have developed a global guidance document to improve the knowledge of TIO in the medical community, enabling the recognition of patients with TIO and appropriate referral. We provide recommendations aiding diagnosis, referral, and treatment, helping promote a global standard of patient management. We reviewed the literature and conducted a three-round Delphi survey of TIO experts. Statements were drafted based on published evidence and expert opinions (≥70% consensus required for final recommendations). Serum phosphate should be measured in patients presenting with chronic muscle pain or weakness, fragility fractures, or bone pain. Physical examination should establish features of myopathy and identify masses that could be causative tumors. Priority laboratory evaluations should include urine/serum phosphate and creatinine to assess renal tubular reabsorption of phosphate and TmP/GFR, alkaline phosphatase, parathyroid hormone, 25-hydroxyvitamin D, 1,25(OH)₂ D, and FGF23. Patients with the clinical/biochemical suspicion of TIO should be referred to a specialist for diagnosis confirmation, and functional imaging should be used to localize causative tumor(s). Recommended treatment is tumor resection or, with unresectable/unidentifiable tumors, phosphate salts plus active vitamin D, or burosumab.

Tumor induced osteomalacia from a peripheral mesenchymal tumour of the foot

Tumour induced osteomalacia (TIO) is a rare condition caused by peripheral mesenchymal tumours (PMT) which produce fibroblast-growth factor 23 (FGF23). FGF23 inhibits renal phosphate reabsorption leading to vitamin D resistant osteomalacia. The rarity of the condition and difficulty with isolating the PMT make diagnosis difficult, with delayed treatment leading to significant patient morbidity. We present a case of PMT of the foot with TIO, with a discussion on diagnosis and treatment.

Long-term use of burosumab for the treatment of tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by tumoral overproduction of FGF-23. Due to local recurrence, we describe the long-term efficacy and safety profile of burosumab, an anti-FGF-23 monoclonal antibody, in a TIO patient after three unsuccessfully surgical attempts.

INTRODUCTION

TIO is a rare paraneoplastic syndrome caused by tumoral overproduction of fibroblast growth factor 23 (FGF23), resulting in hyperphospaturia, hypophosphatemia, and osteomalacia. Surgery is the only definitive treatment, but tumor can locally recur, even after years from primary surgery. Furthermore, some tumors cannot be removed by surgery due to their location.

METHODS

We describe the case of a 54-year-old woman affected by recurrent TIO who, after three unsuccessful surgical attempts of tumor removal, was treated with burosumab, an anti-FGF-23 monoclonal antibody.

RESULTS

The patient was referred to our Bone Unit after experiencing several fractures in different sites, both traumatic and non-traumatic. At the time of first evaluation, at the age of 46, serum-phosphate (SP) was 1.2 mg/dL (reference range (RR) 2.5-4.5), 24-h urinary phosphate was 842 mg (RR 400-1000), and intact-FGF-23 was 117 pg/mL (RR 25-45). Imaging showed a metabolic pre-sacral lesion that firstly underwent to exploratory laparotomy. Then, patient underwent to surgical excision of tumor. After 18 months of well-being, tumor relapsed and even the subsequent surgery was not able to completely remove it. Since 2015, patient was maintained in phosphorus supplements and 1,25(OH)₂vitamin D₃, but SP levels never normalized. In September 2019, she was started on burosumab, initially at the dose of 0.3 mg/kg/month, progressively increased to the current 0.8 mg/kg/month, with great improvement of pain, physical performance, and normalization of SP levels. Burosumab was temporary and cautionary discontinued for COVID-19 pneumonia, with a worsening of SP. After restart of burosumab, biochemistry returned to normal.

CONCLUSIONS

To our knowledge, this is the first European patient affected by TIO treated with burosumab for more than 2 years. Burosumab is a promising therapy in the medical treatment of TIO refractory or not eligible for definitive surgery, with good efficacy and safety profile.

Tumour-induced osteomalacia due to residual benign glomangioma

Tumour-induced osteomalacia (TIO) is a rare paraneoplastic syndrome. The constellation of findings of unprovoked fractures, hypophosphataemia, urinary phosphate wasting and a negative genetic evaluation suggest a TIO diagnosis. Tumours leading to TIO are often small and difficult to localise using standard imaging studies. The 68Ga-DOTATATE CT/positron emission tomography, a somatostatin receptor imaging modality, is the radiographical study of choice for localisation. It is highly sensitive and specific since tumours that cause oncogenic osteomalacia have been shown to express somatostatin receptors. Complete surgical resection is the treatment of choice; however, it may not always be feasible. Burosumab, a human anti-fibroblast growth factor-23 monoclonal antibody, is a therapeutic option in cases of unresectable TIO to normalise phosphorus levels and improve fracture healing. Our patient was initiated on burosumab, which led to healing of his fractures and profound symptomatic improvement of his pain. TIO is often undiagnosed for many years, leading to significant patient morbidity.

Disorders of phosphate homeostasis in children, part 2: hypophosphatemic and hyperphosphatemic disorders

Phosphorus, predominantly in the form of inorganic phosphate PO₄^-3, has many essential physiological functions. In the skeleton, phosphate and calcium form the mineral component and phosphate is also essential in regulating function of skeletal cells. Considerable advances have been made in our understanding of phosphate homeostasis since the recognition of fibroblast growth factor-23 (FGF23) as a bone-derived phosphaturic hormone. This second part of a two-part review of disorders of phosphate homeostasis in children covers hypophosphatemic and hyperphosphatemic disorders that are of interest to the pediatric radiologist, emphasizing, but not limited to, those related to abnormalities of FGF23 signaling.

Phosphaturic mesenchymal tumor in right thigh: 2 cases report and literature review

Background

Phosphaturic mesenchymal tumor (PMT) is a very rare tumor of bone and soft tissue that has no specific clinical manifestations. Here we present 2 cases of PMT in the right thigh, including comparatively adequate immunohistochemistry.

Case Presentation

We described 2 cases of PMT in the right thigh with manifestations of hypophosphatemia. PET-CT examination showed that both patients had lesions with increased expression of somatostatin receptors in the right thigh. Bland cells and dirty calcified stroma were exhibited under the microscope. And immunohistochemical detection of FGF-23 was positive.

Conclusions

PMT is a very uncommon tumor for which diagnosis and treatment are often delayed. Considering the importance of surgery for the treatment of this disease, a full understanding of its clinicopathological features will facilitate the diagnosis of this disease.

Total hip arthroplasty for treatment of femoral neck fracture due to hypophosphatemic osteomalacia: a retrospective case series with mean follow-up of five years

BACKGROUND

To retrospectively characterize the clinical characteristics and efficacy of total hip arthroplasty and the important factors needing attention in hypophosphatemic osteomalacia (HO) patients with hip involvement.

PATIENTS AND METHODS

We performed a review of seven patients (two women and five men) referred to our clinic with a final diagnosis of HO who received total hip arthroplasty between 2010 and 2018. Five patients (Group 1) received proper medical management with or without aetiologic therapy, while the other two patients (Group 2) did not receive due to misdiagnosis. The mean follow-up duration was 5.1 ± 2.0 years.

RESULTS

The patients in Group 1 had significant relief of pain and improved laboratory results. The mean Harris Hip Score of Group 1 increased from 44.2 ± 6.0 to 94.0 ± 3.0, and the mean VAS score decreased from 8.8 ± 0.4 to 1.8 ± 0.7. However, the progressive extensive pain score in Group 2 had no obvious improvement, with the Harris Hip Score increasing from 45.5 ± 0.5 to 60 ± 28.0 and the VAS score decreasing from 9.0 ± 1.0 to 6.5 ± 2.5.

CONCLUSION

THA appears to be an effective method for hip arthritis or joint deformities resulting from hypophosphatemic osteomalacia. A satisfactory outcome of the surgery depends on the early etiological identification, the treatment of hypophosphatemia, a careful operation, and the operative strategies, as well as proper medical treatment.

A literature review to understand the burden of disease in people living with tumour-induced osteomalacia

This study reviews publications to describe the signs, symptoms and impact of tumour-induced osteomalacia (TIO) on patients' burden of disease. TIO is associated with a spectrum of signs and symptoms imposing a significant clinical burden, but the psychosocial impact of this rare disease has been poorly researched so far.

INTRODUCTION

To describe the signs, symptoms and impacts of tumour-induced osteomalacia (TIO) and summarise the state of research on the burden of disease of this ultra-rare condition.

METHODS

A targeted literature review was conducted in PubMed using pre-defined search terms. Relevant articles published between 1980 and 2021 were screened for inclusion. Seventy records were selected for analysis. Data were extracted and grouped into categories and sub-categories to identify recurrent signs, symptoms and impacts of TIO and describe the burden on patients. Chord diagrams were created to analyse the relationships between different TIO outcomes and characterise the presentation of TIO.

RESULTS

Although the number of articles on TIO published have been increasing over the past 20 years, most studies were case reports and case series (n = 65/70) and only few were studies with higher quality of evidence (n = 5/70). Most articles were based on data reported by clinicians (n = 67/70). Patients with TIO experienced a combination of outcomes including chronic pain, weakness, skeletal-related manifestations and limitations in mobility. Only a few studies (n = 2/70) analysed the burden of TIO on the emotional wellbeing and on the work life of the patient.

CONCLUSION

Patients with TIO present with a spectrum of signs and symptoms that impose a significant burden. The impact on the psychosocial wellbeing of patients should be further investigated, as this has been poorly researched so far. Studies with high quality of evidence should be designed to further the understanding of the burden of disease of TIO from the patient's perspective.

Intracranial phosphaturic mesenchymal tumors. A case report and review of literature

Most osteomalacia-inducing tumors (OITs) are phosphaturic mesenchymal tumors (PMTs) that secrete fibroblast growth factor 23 (FGF23). These tumors usually occur in the bone and soft tissues, and intracranial OITs are rare. Therefore, intracranial OIT is difficult to diagnose and treat. This paper presents a case of intracranial OIT and shows a review of previous cases. A 45-year-old man underwent nasal cavity biopsy and treatment with active vitamin D₃ and neutral phosphate for hypophosphatemia. Amplification of FGF23 mRNA level within the tumor was detected. Subsequently, the surgical specimen was diagnosed with a PMT and was considered the cause of the patient's osteomalacia. The patient was referred to a neurosurgery department for the excision of the intracranial tumor extending to the nasal cavity. After tumor removal, the serum levels of FGF23 and phosphorus were normalized as compared to preoperative those. The patient remains disease-free, without additional treatment, approximately 10 years after surgery, with no tumor recurrence. As per the literature, intracranial OITs usually occur in patients aged 8-69 years. Bone and muscle pain are major complaints. Approximately 60% of the patients reported previously had symptoms because of intracranial tumors. In some cases, it took several years to diagnose OIT after the onset of the osteomalacia symptoms. Laboratory data in such cases show hypophosphatemia and elevated FGF23 levels. Because FGF23 levels are associated with the severity of osteomalacia symptoms, total tumor resection is recommended. PMT and hemangiopericytoma (HPC) are histologically similar, but on immunochemistry, PMT is negative for signal transducer and activator of transcription 6 (STAT6), whereas HPC is positive. FGF23 amplification is seen in PMTs but not in HPCs. Therefore, the analysis of FGF23 and STAT6 was helpful in distinguishing PMTs from HPCs. In cases of hypophosphatemia and osteomalacia without a history of metabolic, renal, or malabsorptive diseases, the possibility of oncogenic osteomalacia should be considered.

Challenging case of tumour-induced osteomalacia

Tumour-induced osteomalacia (TIO), also known as oncogenic osteomalacia, is an uncommon paraneoplastic syndrome which poses a diagnostic challenge. The hallmark feature is severe acquired hypophosphataemic osteomalacia due to renal phosphate wasting because of increased secretion of fibroblast growth factor 23 (FGF-23). A man in his 30s, presented with a 4-year history of severe muscle aches, bone pain and proximal muscle weakness, was referred for evaluation. His laboratory examination revealed severe hypophosphataemia as a result of urinary phosphate wasting, low 1,25-dihydroxyvitamin D, high alkaline phosphatase and elevated FGF-23. We could localise the tumour to his right femur and the biopsy showed a mesenchymal origin. The treatment with pharmacotherapy and radiofrequency ablation helped in the normalisation of blood chemistry and resulted in significant clinical improvement. Hypophosphataemia, phosphaturia, elevated FGF-23 and low 1,25-dihydroxyvitamin D level with severe musculoskeletal pain and muscle weakness necessitate careful evaluation of TIO.

Tumor-induced osteomalacia: a case report

Background

Tumor-induced osteomalacia is a rare, acquired paraneoplastic syndrome, including hypophosphatemia, high serum alkaline phosphatase, reduced active vitamin D, suboptimal bone mineral density, bone pain, fragility fractures, and muscle weakness.

Case presentation

We report a case of 74–year–old male of mixed ancestry with hypophosphatemia resistant to treatment despite optimal compliance, associated with profound reduction of bone mineral density and multiple nontraumatic fractures, including bilateral rib fractures, lower-thoracic (T11, T12) vertebrae, and two fractures involving the surgical and anatomical neck of the right humerus. We discuss an approach to identifying the underlying cause of hypophosphatemia associated with fragility fractures, and options for management of this rare condition.

Conclusion

Although rare, tumor-induced osteomalacia can be diagnosed if a logical stepwise approach is implemented. Surgery could be curative if the tumor is properly located and is resectable.

Rare Diseases That Impersonate One Another: X‐Linked Hypophosphatemia and Tumor‐Induced Osteomalacia, a Retrospective Analysis of Discriminating Features

Tumor‐induced osteomalacia (TIO) is a rare paraneoplastic disease characterized by frequent fractures, bone pain, muscle weakness, and affected gait. The rarity of TIO and similar presentation to other phosphate‐wasting disorders contribute to a high misdiagnosis rate and long time to correct diagnosis. TIO is curable by tumor resection, so accurate diagnosis has significant impact on patients' emotional and economic burden. Current diagnostics for TIO rely on decades‐old literature with poor phenotypic validation. Here, we identify salient clinical differences between rigorously validated cohorts of patients with TIO (n = 9) and X‐linked hypophosphatemia (XLH; n = 43), a frequent misdiagnosis for patients with TIO. The TIO cohort had significantly elevated FGF23 (365 versus 95 RU/mL, p < 0.001) and alkaline phosphatase (282.8 versus 118.5 IU/L, p < 0.01) but significantly reduced phosphorus (1.4 versus 2.2 mg/dL, p < 0.05) and 1,25(OH)₂ D (16.6 versus 59.8 pg/mL, p < 0.01). By contrast, total vitamin D was similar between the two groups. Dual‐energy X‐ray absorptiometry (DXA) scans reveal lower Z‐scores in the hip (−1.6 versus 0.050, p < 0.01) and spine (0.80 versus 2.35, p < 0.05). TIO patients were more likely to have prior clinical diagnosis of osteoporosis (67% versus 0%), use assistive devices in daily living (100% versus 14%), and have received a knee arthroplasty (33% versus 7%). TIO patients lost an average of 1.5 cm over their disease course and had sustained an average of 8 fractures each, whereas fractures were rare in XLH. The XLH cohort had higher incidence of osteotomy (19% versus 0%), spinal stenosis (12% versus 0%), secondary dental abnormalities (95% versus 44%, p < 0.001), and depression and anxiety (46.5% versus 11%). These results deepen our understanding of the subtle differences present between diseases of phosphate wasting. They suggest several biochemical, clinical, and historical features that effectively distinguish TIO from XLH. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

An Expert Perspective on Phosphate Dysregulation With a Focus on Chronic Hypophosphatemia

Because of their rarity, diseases characterized by chronic hypophosphatemia can be underrecognized and suboptimally managed, resulting in poor clinical outcomes. Moreover, serum phosphate may not be measured routinely in primary care practice. Authors participated in several working sessions to advance the understanding of phosphate homeostasis and the causes, consequences, and clinical implications of chronic hypophosphatemia. Phosphate levels are regulated from birth to adulthood. Dysregulation of phosphate homeostasis can result in hypophosphatemia, which becomes chronic if phosphate levels cannot be normalized. Chronic hypophosphatemia may be underrecognized as serum phosphate measurement is not always part of routine analysis in the primary care setting and results might be misinterpreted, for instance, due to age-specific differences not being accounted for and circadian variations. Clinical consequences of chronic hypophosphatemia involve disordered endocrine regulation, affect multiple organ systems, and vary depending on patient age and the underlying disorder. Signs and symptoms of chronic hypophosphatemic diseases that manifest during childhood or adolescence persist into adulthood if the disease is inadequately managed, resulting in an accumulation of clinical deficits and a progressive, debilitating impact on quality of life. Early identification and diagnosis of patients with chronic hypophosphatemia is crucial, and clinical management should be started as soon as possible to maximize the likelihood of improving health outcomes. Furthermore, in the absence of a universally accepted description for "chronic hypophosphatemia," a definition is proposed here that aims to raise awareness of these diseases, facilitate diagnosis, and guide optimal phosphate management strategies by improving monitoring and assessment of patient response to treatment. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Favorable effects of burosumab on tumor-induced osteomalacia caused by an undetectable tumor: A case report

RATIONALE

Tumor-induced osteomalacia (TIO) is curable by tumor resection, but detection of the tumor can be challenging. Overproduction of fibroblast growth factor 23 (FGF23) by the tumor causes hypophosphatemia and consequently induces inappropriate bone turnover. Conventionally oral phosphate supplementation was the only treatment for TIO, but had risks of hypercalciuria and nephrocalcinosis. Burosumab, a human monoclonal anti-FGF23 antibody, was recently post-marketed in Japan against for FGF23-related hypophosphatemia. Herein, we present a case of TIO with undetectable tumor that was successfully treated with burosumab.

PATIENT CONCERNS

A 47-year-old woman was forced to use a wheelchair because of pain in both feet.

DIAGNOSIS

Laboratory findings showed hypophosphatemia, elevated bone markers, and high serum FGF23 without renal tubular defects. Imaging studies revealed bone atrophy in the feet, decreased bone density, and multiple pseudofractures in the talar, sacral, and L5 vertebral regions. After excluding drug-induced and hereditary osteomalacia, we diagnosed her as TIO.

INTERVENTIONS

Comprehensive imaging studies and stepwise venous sampling failed to localize the tumor, and we started to administer subcutaneous burosumab.

OUTCOMES

After administration of burosumab, her serum phosphate was normalized without phosphate supplementation within 2 months. Improvement of pseudofractures, relief of pain evaluated by a visual analog scale, and normalization of bone biomarkers were observed. The patient was able to stand by herself after 6 months administration of burosumab.

LESSONS

This is the first report in clinical practice to demonstrate favorable effects of burosumab, including not only normalization of serum phosphate but also improvements of pseudofractures and subjective pain, in a patient with TIO and undetectable tumor.

Tumor induced osteomalacia: A single center experience on 17 patients

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome due to a phosphaturic tumor, which overproduces Fibroblast Growth Factor 23 (FGF-23), causing hyperphosphaturia, hypophosphatemia, low 1,25(OH)₂D and osteomalacia. Tumor localization is critical, diagnostic delay ranges from 2.5 to 28 years and to date surgical removal is considered effective treatment. We retrospectively evaluated patients with definite diagnosis of TIO referred to a tertiary Rheumatology Center between September 2000 and May 2020, investigating clinical management and disease outcome. We included 17 patients: 10 (58.8%) were females, mean age at diagnosis was 55.3 ± 13.9 years (mean ± standard deviation), with a diagnostic delay from symptoms onset to tumor detection of 6.6 ± 6.25 years. Biochemical data were: serum phosphorus 1.3 ± 0.4 mg/dL (Reference Range: 2.5-4.6), serum 1,25(OH)₂D 31.8 ± 22.9 ng/mL (RR: 25-86), intact FGF-23, 358.9 ± 677 pg/mL (RR: 25-45); 24 h-Urine Phosphorus was increased in only 2 patients, while tubular reabsorption of phosphate (TRP) was decreased in all patients confirming a renal phosphate wasting. In 2013 ⁶⁸Ga- DOTA-based PET/CT was introduced in routinely practice and diagnostic delay was consistently reduced (from 8.6 ± 7.9 to 4.3 ± 2.4 years). Thirteen patients underwent surgery, one patient underwent radiofrequency ablation; 3 patients, not eligible for surgery, were treated only with supplements of phosphorus and calcitriol. One was started on Burosumab after several unsuccessful surgical attempts. After surgery or ablation, 8 patients had complete remission, 3 TIO persistence, and 3 had overtime relapse. Relapses were observed only in patients who previously underwent closed biopsy. To our knowledge, this is the widest European cohort of TIO patients in the last two decades. We confirm a usual diagnostic delay and recommend a stepwise diagnostic approach. Tumor biopsy is not recommended due to the potential cell spilling. Surgery is generally considered a definitive treatment, even though other approaches have been successful in curing TIO. Active surveillance on possible recurrence is always needed. Burosumab appears a promising therapy.

Diagnosis and Management of Tumor-induced Osteomalacia: Perspectives From Clinical Experience

Purpose

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome of abnormal phosphate and vitamin D metabolism caused by typically small endocrine tumors that secrete fibroblast growth factor 23 (FGF23). TIO is characterized clinically by progressive musculoskeletal pain, fatigue, proximal muscle weakness, and multiple fractures, leading to long-term disability. Misdiagnosis and delayed diagnosis are common because of the nonspecific symptoms, and several years may elapse before patients receive an accurate diagnosis and appropriate treatment. Thus, it is vital that awareness of the appropriate recognition and management of TIO is increased among healthcare professionals who may encounter patients with suspected TIO.

Methods

A roundtable meeting was held on 10 January 2020 in Dallas, TX, USA, to gather perspectives on the diagnosis and treatment of TIO. The following topics were considered: clinical presentation, patient history, differential diagnosis, laboratory assessment, imaging, venous sampling, and treatment.

Results

This report provides a summary of our collective experiences in the management of TIO.

Main conclusions

Laboratory tests are mandatory to expedite TIO diagnosis and should include measurement of fasting serum phosphorus, renal phosphate reabsorption, serum 1,25-dihydroxyvitamin D, and serum FGF23 levels. Functional and anatomical imaging are essential to locate the FGF23-secreting tumor(s) causing TIO. Surgical resection is often a curative treatment when the tumor can be localized; however, better management of patients who cannot be operated on with targeted therapies is needed. Further efforts to increase awareness of TIO within the medical community, and education on recommended diagnostic and treatment pathways are required to improve the management of this debilitating disease.

Early Discrimination Between Tumor-Induced Rickets/Osteomalacia and X-Linked Hypophosphatemia in Chinese Children and Adolescents: A Retrospective Case-Control Study

In children and adolescents, distinguishing tumor-induced rickets/osteomalacia (TIR/O) from hereditary hypophosphatemic rickets/osteomalacia (HR/O) is a medical challenge. We retrospectively studied 10 Chinese children and adolescents with TIR/O who underwent surgery at a mean age of 17.4 ± 2.1 years and compared their characteristics to 24 age- and sex-matched patients with X-linked hypophosphatemia (XLH). Positive family history of HR/O and dental problems, such as enamel hypoplasia and dental abscess, were reported in 8 (33.3%) and 5 (20.8%) patients with XLX, respectively, but not in patients with TIR/O. In addition, in comparison with XLH patients, TIR/O patients had an older disease onset age (150 versus 24 months, p < 0.001), a higher height standard deviation score (SDS; -1.2 ± 1.8 versus -4.0 ± 1.4, p < 0.001), a lower Z-score of bone mineral density (BMD) at lumbar spine (LS) (-3.9 [6.0] versus +1.8 [7.0], p < 0.001), and a higher serum intact fibroblast growth factor 23 (FGF23) level (500.27 ± 87.20 versus 121.71 ± 70.94 pg/mL, p < 0.001), corresponding to a lower serum phosphate level (0.52 ± 0.07 versus 0.64 ± 0.11 mmol/L, p = 0.005) and a higher serum alkaline phosphatase (ALP) level (557 [631] versus 305 [249] U/L, p = 0.005). We generated receiver operating characteristic (ROC) curves and calculated the area under the ROC curve (AUC). The AUCs of onset age, FGF23, and LS Z-score were equal to 1, suggesting that these are excellent indices for the differential diagnosis between TIR/O and XLH. In summary, our study furthers our understanding of the spectrum of clinical, biochemical, and pathologic findings associated with TIR/O. For children and adolescent patients with HR/O, a comprehensive and careful clinical and laboratory evaluation is of great importance, and we recommend enquiry of the family history, onset age, and dental problems, as well as measurement of serum FGF23 and BMD. © 2021 American Society for Bone and Mineral Research (ASBMR).

Renal Phosphate Wasting Due to Tumor-Induced (Oncogenic) Osteomalacia

Osteomalacia is a widely prevalent bone disorder that is caused by an imbalance in body calcium and phosphate. Tumor-induced osteomalacia (TIO) is a rare form of osteomalacia that is associated with mesenchymal tumors. It is caused by overproduction of fibroblast growth factor 23 (FGF-23), a hormone involved in phosphate regulation.

A 59-year-old male with a history of factor V Leiden mutation, pulmonary embolism, and deep vein thrombosis was diagnosed with oncogenic osteomalacia in 2008 following laboratory findings significant for low phosphorus and elevated FGF-23 levels. He underwent a resection of a right suprascapular notch mass with the biopsy confirming a phosphaturic mesenchymal tumor. He was maintained on oral phosphorus and calcitriol replacements with a regular follow-up with oncology and nephrology. Eight years later, the patient’s phosphorus levels started declining despite replacement. A repeat test showed FGF-23 levels once again elevated. A whole-body magnetic resonance imaging (MRI) scan showed no significant findings. The patient was continued on oral replacement therapy with a close follow-up. Two years later, urine phosphorus excretion was elevated at 2494 mg per 24 hours with low plasma phosphorus (1.2 mg/dL) and an elevated FGF-23 level of 1005 relative units (RU)/mL. A repeat MRI of the right shoulder revealed a mass in the supraspinatus muscle and another in the spinal glenoid notch. The masses were resected and the biopsy was consistent with a recurrence of the phosphaturic mesenchymal tumor. Follow-up serum phosphate levels remained in the normal range.

FGF-23 plays a critical role in bone mineralization through the regulation of phosphate levels. Overproduction, as seen in mesenchymal tumors, results in hyperphosphaturia, hypophosphatemia, and low calcitriol levels. While the definitive treatment of TIO involves the resection of the mesenchymal tumor, localization of the tumor is often challenging given its small size and slow growth. This leads to delayed diagnosis and treatment. For individuals whose tumor cannot be resected or detected, burosumab is the preferred form of therapy. Interestingly, FGF-23 is shown to have a potential cardiovascular (CV) morbidity and mortality through various mechanisms like activation of myocardial FGF-23 receptors, endothelial dysfunction, inflammation, and altered phosphorus and vitamin D metabolisms. While studies have shown possible FGF-23 effects on CV outcomes in patients with chronic kidney disease, this has not been proven in cases of TIO.

The genetic polymorphisms of XPR1 and SCL34A3 are associated with Fanconi syndrome in Chinese patients of tumor-induced osteomalacia

PURPOSE

Tumor-induced osteomalacia (TIO) is an acquired form of hypophosphatemia caused by tumors with excess production of fibroblast growth factor 23 (FGF23). Some reports showed that TIO patients had renal Fanconi syndrome (FS) with unidentified mechanism. In this study, we investigated the association between genetic polymorphisms of phosphate transporters in renal proximal tubules and TIO with FS.

METHODS

We recruited 30 TIO patients with FS (TIO-FS) as well as 30 TIO patients (TIO-nonFS) without any urine abnormalities matched by age and gender. We collected clinical manifestations and conducted targeted sequencing of SLC34A1, SLC34A3 and XPR1 genes and the association analysis between variants in TIO with FS and phenotypes.

RESULTS

TIO-FS group had lower levels of serum phosphate (0.44 ± 0.12 vs. 0.51 ± 0.07 mmol/L, p < 0.05) than TIO-nonFS group. Among the 16 SNPs in SLC34A1, SLC34A3 and XPR1 genes, GG/GC genotypes of rs148196667 in XPR1 and AA/TA genotypes of rs35535797 in SLC34A3 were associated with a reduced susceptibility to have FS. The G allele of rs148196667 in XPR1 decreased the risk of FS. The GGAA haplotype in SLC34A3 and GCT haplotype in XPR1 were associated with a decreased risk for FS.

CONCLUSIONS

The polymorphisms of XPR1 and SCL34A3 are associated with TIO patients with Fanconi syndrome. It provides novel insight to the relationship of phosphate transportation and general functions of renal proximal tubules.

Application of ultrasound-guided biopsy and percutaneous radiofrequency ablation in 2 cases with phosphaturic mesenchymal tumor and literature review

Tumor-induced osteomalacia (TIO) is a vanishingly rare paraneoplastic syndrome which is usually caused by phosphaturic mesenchymal tumors (PMTs). The conventional treatment for PMTs is total resection, and ultrasound-guided radiofrequency ablation (RFA) can also be used for the treatment of PMTs patients, especially for patients in whom complete resection may lead to serious complications. We report two cases with PMT who presented syndrome with progressive musculoskeletal complaints and performed ultrasound-guided biopsy and RFA. Ultrasound-guided RFA, which is a safe and effective minimally invasive treatment option, appears to be a valuable alternative to surgery for patients presenting with PMT. We are the first reported case of RFA guided by ultrasonography in the treatment of PMT.

A case report of mesenchymal scapular FGF secreting tumor: Importance of follow up in tumor induced osteomalacia

A 46-year-old Asian male with history of atraumatic fracture of femur (requiring the use of a walker), muscle cramps and loosening teeth presents to Endocrine clinic. He had elevated parathyroid hormone, severely low phosphorus, elevated bone-specific ALP, with normal serum and urine calcium. He was found to have elevated FGF 23 levels, but initial functional and anatomic imaging was negative for any localizing tumor. With persistent follow-up and serial imaging, after 3 years, a 2.2 cm right scapular mass was found on MRI. Since it was also visualized on PET/CT, this was suspected to be the cause of his severe hypophosphatemia. He underwent surgical excision and pathology revealed a phosphaturic mesenchymal tumor after excision. Tumor induced osteomalacia is a rare, acquired paraneoplastic syndrome in which a tumor that secretes FGF23 leads to decreased renal phosphate reabsorption, resulting in hypophosphatemia, and bone demineralization. Diagnosis is challenging as common presenting symptoms are nonspecific, but when followed up closely with proper diagnostic modalities, identification & removal of the culprit lesion is usually curative.

Onconephrology: The intersections between the kidney and cancer

Onconephrology is a new subspecialty of nephrology that recognizes the important intersections of kidney disease with cancer. This intersection takes many forms and includes drug-induced nephrotoxicity, electrolyte disorders, paraneoplastic glomerulonephritis, and the interactions of chronic kidney disease with cancer. Data clearly demonstrate that, when patients with cancer develop acute or chronic kidney disease, outcomes are inferior, and the promise of curative therapeutic regimens is lessened. This highlights the imperative for collaborative care between oncologists and nephrologists in recognizing and treating kidney disease in patients with cancer. In response to this need, specific training programs in onconephrology as well as dedicated onconephrology clinics have appeared. This comprehensive review covers many of the critical topics in onconephrology, with a focus on acute kidney injury, chronic kidney disease, drug-induced nephrotoxicity, kidney disease in stem cell transplantation, and electrolyte disorders in patients with cancer.

Hiding in plain sight: Gene panel and genetic markers reveal 26-year undiagnosed tumor-induced osteomalacia of the rib concurrently misdiagnosed as X-linked hypophosphatemia

Tumor-induced osteomalacia (TIO), caused by phosphaturic mesenchymal tumors (PMTs), is a rare paraneoplastic syndrome characterized by frequent bone fractures, bone pain, muscle weakness, and affected gait. These tumors typically secrete high levels of Fibroblastic Growth Factor 23 (FGF23), a hormone which acts on the kidney to cause hypophosphatemia, ultimately impairing bone mineralization. In this case report, we present a 41-year-old female with FGF23-mediated hypophosphatemia with a 26-year delay in TIO diagnosis and a concurrent misdiagnosis of X-linked hypophosphatemic rickets (XLH). Given an absence of family history of hypophosphatemia, a 13-gene hypophosphatemia panel including XLH (PHEX gene) was performed and came back negative prompting a diagnostic search for a PMT causing TIO. A ⁶⁸Ga-DOTATATE PET/CT scan revealed the presence of a 9th right rib lesion, for which she underwent rib resection. The patient's laboratory values (notably serum phosphorus, calcium, and vitamin D) normalized, with FGF23 decreasing immediately after surgery, and symptoms resolving over the next three months. Chromogenic in situ hybridization (CISH) and RNA-sequencing of the tumor were positive for FGF23 (CISH) and the transcriptional marker FN1-FGFR1, a novel fusion gene between fibronectin (FN1) and Fibroblast Growth Factor Receptor 1 (FGFR1), previously determined to be present in the majority of TIO-associated tumors. This case demonstrates the notion that rare and diagnostically challenging disorders like TIO can be undiagnosed and/or misdiagnosed for many years, even by experienced clinicians and routine lab testing. It also underscores the power of novel tools available to clinicians such as gene panels, CISH, and RNA sequencing, and their ability to characterize TIO and its related tumors in the context of several phenotypically similar diseases.

Effects of burosumab on osteocalcin and bone mineral density in patient with 15-year history of nonremission tumor-induced osteomalacia initially treated with conventional therapy: Case report

Excess fibroblast growth factor 23 (FGF23) causes hypophosphatemic osteomalacia, which is associated with impaired bone matrix mineralization. Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by over-secretion of FGF23 from a tumor. Burosumab, a fully human monoclonal antibody with activities against FGF23, was initially approved in Japan before the rest of the world for treatment of FGF23-associated hypophosphatemic osteomalacia by TIO. We report here a patient with a 15-year history of non-remission TIO initially treated with conventional therapy who was then switched to burosumab treatment. Persistent hypophosphatemia and a relative low level of osteocalcin (bone Gla protein, BGP) compared with bone alkaline phosphatase (BAP) level, indicating poor matrix mineralization, developed during long-term conventional therapy. Repeated surgical and stereotactic body radiation treatments did not result in complete resection of the causable tumor, and bone mineral density (BMD) gradually decreased. Ultimately, burosumab treatment was administered and the serum Pi concentration immediately normalized, while both BGP and BMD also showed a good response. This is first known case report of the detailed efficacy of burosumab for nonremission TIO as an alternative to conventional therapy.

Clinical Characteristics and Surgical Outcomes of Sinonasal Lesions Associated With Tumor-Induced Osteomalacia

OBJECTIVE

To investigate the clinical characteristics and surgical outcomes of sinonasal tumors associated with tumor-induced osteomalacia (TIO).

STUDY DESIGN

Retrospective case series.

SETTING

Single tertiary center.

METHODS

We studied the clinical characteristics and surgical outcomes of 43 patients (22 male, 21 female) who had lesions in the nasal cavity and paranasal sinus associated with TIO and underwent surgery between August 2006 and November 2019.

RESULTS

The mean ± SD duration between the onset of symptoms and surgery was 3.9 ± 2.6 years. The most common tumor site was the ethmoid sinus (76.7%), and the skull base was involved in 12 cases. Phosphaturic mesenchymal tumors were diagnosed in 41 patients, among whom there was 1 multifocal case. Another 2 cases involved odontogenic fibroma and hemangiofibroma, respectively. Serum phosphorus normalized in 39 cases within 4.4 ± 2.3 days, and serum fibroblastic growth factor 23 normalized within 1 day; clinical symptoms, however, gradually improved within several months after the first operation. There was no significant difference in the recovery rate between endoscopic and open surgery (P = 0.639). Two patients with recurrent cases and 2 with nonremission cases recovered after a sinonasal reoperation. The patient with a multifocal case recovered after the resection of the tumors in the ethmoid sinus and mandible. The overall recovery rate was 97.7%.

CONCLUSION

Most sinonasal tumors associated with TIO are located in the ethmoid sinus, and the skull base is involved in some cases. Complete excision of the tumor leads to recovery, and endoscopic surgery could achieve recovery rates similar to those of open surgery.

Tumor-Induced Osteomalacia and the Importance of Plasma Fibroblast Growth Factor 23 as an Indicator: Diagnostic Delay Leads to a Suicide Attempt

Tumor-induced osteomalacia is a rare hypophosphatemic disease caused by unregulated production of fibroblast growth factor 23 by a tumor, thereby inducing renal phosphate wasting and inhibiting appropriate increase of calcitriol production. Symptoms of tumor-induced osteomalacia, including muscle weakness, bone pain, and pathologic fractures, are nonspecific and warrant further workup. We report the case of a 50-year-old African American female with no known psychiatric illness who was admitted after a failed suicide attempt provoked by severe bone pain. She had been treated for fibromyalgia and hypophosphatemic rickets at other facilities with no improvement. The findings of profound renal phosphate wasting initiated further evaluation, which revealed an elevated fibroblast growth factor 23 level and a right proximal fibular mesenchymal tumor on octreotide scintigraphy. Magnetic resonance imaging confirmed the findings of a solid intramuscular tumor corresponding to the octreotide avid lesion. After wide excision of the tumor, serum phosphate and parathyroid hormone levels began to normalize. This case highlights the importance of extensively investigating the cause of bone pain, weakness, and fatigue in patients without a family history of hypophosphatemia or bone disorders. The aforementioned symptoms may precede recurrent pathological fractures, and a thorough workup ensures that a diagnosis of tumor is not delayed or overlooked, as tumor resection confers a favorable prognosis and dramatic increase in the quality of life for patients.

Neurofibromatosis type 1 associated with hypophosphatemic osteomalacia due to hypersecretion of fibroblast growth factor 23: a case report

BACKGROUND

Neurofibromatosis type 1 is characterized by multiple café au lait spots and cutaneous and plexiform neurofibromas, and is one of the most common autosomal dominant hereditary disorders caused by mutations of the neurofibromatosis type 1 tumor suppressor gene. Osteomalacia in neurofibromatosis type 1 is very rare and is characterized by later onset in adulthood. In humans, fibroblast growth factor 23, which is a causative factor of tumor-induced osteomalacia, is not only a paracrine and autocrine factor, but is also a physiological regulator of phosphate balance in normal serum.

CASE PRESENTATION

Our patient was a 65-year-old Japanese woman whose neurofibromas began to appear when she was in elementary school. At age 28, she was diagnosed as having neurofibromatosis type 1. A spinal compression fracture and multiple rib fractures were identified in 2012 and 2017, respectively. Her laboratory findings revealed hypophosphatemia due to renal phosphate wasting and a high serum level of fibroblast growth factor 23. Neurofibromas located on the surface of her right forearm and left upper arm, in which a slight abnormal accumulation of tracers was observed on ¹¹¹indium-pentetreotide scintigraphy, were surgically removed, but there was no improvement in hypophosphatemia or serum fibroblast growth factor 23 after surgery. Therefore, we administered eldecalcitol, which also failed to produce improvement in abnormal data. Subsequent combination with dibasic calcium phosphate hydrate led to improvement in some of the abnormalities, including hypophosphatemia. Immunohistochemical staining using anti-human fibroblast growth factor 23 antibody revealed slightly positive results, however, only one out of three amplifications of the fibroblast growth factor 23 gene was observed by real-time polymerase chain reaction, and no clear fibroblast growth factor 23 gene expression in the resected neurofibromas could be confirmed.

CONCLUSIONS

We here describe a first rare case of a 65-year-old woman with neurofibromatosis type 1 associated with hypophosphatemic osteomalacia in which a high serum fibroblast growth factor 23 level was confirmed.

Lessons learnt from delayed diagnosis of FGF-23-producing tumour-induced osteomalacia and post-operative hungry bone syndrome

Tumour-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by a fibroblast growth-factor-23 (FGF-23)-secreting phosphaturic mesenchymal tumour (PMT) and is characterised by hypophosphataemic osteomalacia. We present a 36-year-old man initially presenting with diffuse bone and joint pain who was inappropriately treated for presumed ankylosing spondylitis for 2 years. Whole-body bone scan suggested metabolic bone disease, prompting referral to our endocrine institution. He was subsequently diagnosed with persistent hypophosphataemia, inappropriately high renal tubular phosphate excretion, 1,25-dihydroxyvitamin D₃ suppression, severe osteoporosis and severe osteomalacia. FGF-23 concentrations (140 ng/L) were raised 3-fold above the upper limit of normal. Initial Gallium-68 (⁶⁸Ga) DOTATATE positron emission tomography (PET)/CT scan missed an active lesion in the left fibular head as the field only included the mid-brain to the proximal femora. Histopathology results from tumour resection confirmed a PMT over-expressing FGF-23. Serum phosphate and FGF-23 normalised immediately post-operatively. He developed severe hypocalcaemia 3-weeks post-operatively (1.77 mmol/L) which normalised after 1 month of high-dose caltrate and calcitriol therapy. Osteomalacia, osteoporosis and associated symptoms resolved during medium-term follow-up with >100% improvement in his bone mineral density. This case report and discussion highlights the pitfalls contributing to delayed diagnosis of TIO and alerts clinicians to the potential complication of hungry bone syndrome post-tumour resection.

Multidisciplinary patient care in X-linked hypophosphatemic rickets: one challenge, many perspectives

X‑linked hypophosphatemic rickets (XLH, OMIM #307800) is a rare genetic metabolic disorder caused by dysregulation of fibroblast-like growth factor 23 (FGF23) leading to profound reduction in renal phosphate reabsorption. Impaired growth, severe rickets and complex skeletal deformities are direct consequences of hypophosphatemia representing major symptoms of XLH during childhood. In adults, secondary complications including early development of osteoarthritis substantially impair quality of life and cause significant clinical burden. With the global approval of the monoclonal FGF23 antibody burosumab, a targeted treatment with promising results in phase III studies is available for children with XLH. Nevertheless, complete phenotypic rescue is rarely achieved and remaining multisystemic symptoms demand multidisciplinary specialist care. Coordination of patient management within the major medical disciplines is a mainstay to optimize treatment and reduce disease burden. This review aims to depict different perspectives in XLH patient care in the setting of a multidisciplinary centre of expertise for rare bone diseases.

Detection Rate of Culprit Tumors Causing Osteomalacia Using Somatostatin Receptor PET/CT: Systematic Review and Meta-Analysis

Background: Tumor-induced or oncogenic osteomalacia (TIO) is a rare paraneoplastic syndrome in which osteomalacia is a consequence of fibroblast growth factor 23 (FGF23) secretion by a mesenchymal tumor. The localization of the culprit lesion in patients with TIO is often challenging. Several studies have evaluated the detection rate (DR) of these tumors using somatostatin receptor positron emission tomography (SSTR-PET/CT). We aimed to summarize literature findings on this topic providing pooled estimates of DR. Methods: A comprehensive literature search by screening PubMed, Embase and Cochrane library electronic databases through August 2019 was performed. The pooled DR of culprit tumors using SSTR-PET/CT in patients with TIO was calculated using a random-effects statistical model. Results: Fourteen studies on the use of SSTR-PET/CT in detecting the culprit tumor in patients with TIO were included in the qualitative analysis. The pooled DR of SSTR-PET/CT on a per-patient-based analysis calculated using eleven studies (166 patients) was 87.6% (95% confidence interval (95% CI) 80.2–95.1%). Statistical heterogeneity among studies was detected (I-square = 63%), likely due to the use of different radiolabeled somatostatin analogues, as demonstrated by a subgroup analysis. Conclusions: Despite limited literature data due to the rarity of the disease, SSTR-PET/CT demonstrated a very high DR of culprit tumors in patients with TIO and it could be used as first-line imaging method for this indication.

Phosphaturic mesenchymal tumor: Case report

Phosphaturic mesenchymal tumors (PMT) are an extremely rare pathologic phenomenon that presents as paraneoplastic tumor-induced osteomalacia. Their diagnosis is often significantly delayed due to their rare occurrence in addition to the generalized and vague symptoms of their presentation including progressive bone pain, myopathies, arthralgias, fractures, and generalized weakness. This case report identifies a very characteristic presentation of a 37-year old African American male suffering from a PMT; with symptom onset presenting over 5-years prior to presentation with a consistent complaint of progressive and debilitating quadriparesis. The tumor was first identified by pelvic computerized tomography, although it was initially thought to be a noncontributory benign soft tissue mass. It was only after being hospitalized due to a severe and unresponsive hypophosphatemic state (less than 1 mg/dl) that the collective differential switched to one of a PMT with follow up nuclear 99mTc bone scintigraphy and magnetic resonance imaging being used to aid in the overall assessment of changes, extent, and general metabolic properties of the tumor. The confirmatory diagnosis of a PMT was later established through both serum fibroblast growth factor 23 testing and histopathologic review of the surgically removed specimen. By including this rare but curative disease into the differential of osteomalacia and thereby further examining patient serum phosphate levels, the previous 5-7 year delay in diagnosis will be dramatically reduced.