Tumour-induced osteomalacia: a literature review and a case report

Tumour-induced osteomalacia

Tumour-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by increased production of fibroblast growth factor 23 (FGF-23). A 45-year-old man presented to us with progressive weakness over 2 years along with recurrent fractures with minimal trauma. His FGF-23 was found to be above the normal range and DOTATATE positron emission tomography (PET) scan showed a well-defined enhancing soft tissue density involving the left posterior ethmoid with extension to the spheno-ethmoidal recess and sphenoid sinus ostium. He underwent endoscopic sinus surgery and excision of the tumour. Histopathological examination showed features of phosphaturic mesenchymal tumour-mixed connective tissue type. Postoperatively the serum phosphorus level increased from day 1 and reached the normal value of 2.5 mg/dl on day 3. He was discharged and continued on oral calcium and vitamin D3. Gradually his myalgia improved and he started walking independently over the next 1 month. The mean delay from symptom onset to treatment in our patient was 2 years and 5 months. Timely diagnosis and meticulous follow-up are necessary for the management of patients with this rare disorder.

A Rare Case of Phosphaturic Mesenchymal Tumor Distal Femur in a Young Female

Introduction

Phosphaturic mesenchymal tumors (PMTs) are rare bone neoplasms with diverse clinical presentations, often posing diagnostic challenges.

Case Report

We describe the case of a 37-year-old female schoolteacher with a PMT localized in the distal femur. Diagnostic indicators included hypophosphatemia, hyperphosphaturia, elevated fibroblast growth factor-23 levels, and clinical symptoms of osteomalacia. Surgical management involved tumor resection and limb salvage surgery with a megaprosthesis. The post-operative period was uneventful, leading to a stable discharge. On follow-up, the patient showed no signs of recurrence, regained full ambulation, remained pain-free, and resumed teaching comfortably.

Conclusion

This case highlights the importance of considering PMT in patients with unusual clinical symptoms, accompanied by hypophosphatemia, hyperphosphaturia, and osteomalacia, and demonstrates successful surgical management, leading to a favorable outcome.

FGF23-secreting sinonasal tumour presenting with acute subdural haemorrhage and tumour-induced osteomalacia

A female in her 50s developed a headache, collapsed and was noted to have an acute atraumatic subdural haemorrhage (SDH) requiring surgical evacuation and intracranial pressure-directed therapy. Her background included recurrent epistaxis, severe generalised bone pain and multiple insufficiency fractures and an undifferentiated autoimmune connective tissue disease. Chronic hypophosphataemia, elevated alkaline phosphatase and raised fibroblast growth factor 23 (FGF23) were also noted. An MRI head and subsequent 68Ga CT/positron emission tomography scan demonstrated an intensely avid tumour in the right ethmoid sinus, extending intracranially. Phosphate was aggressively replaced, and alfacalcidol was initiated to circumvent the effects of FGF23 on her kidneys and bone minerals. The tumour was biopsied and then definitively resected via combined endonasal and craniotomy approaches, resulting in good clinical improvement. FGF23 titre and serum phosphate both normalised leaving the diagnosis of a phosphaturic mesenchymal tumour-secreting FGF23, leading to tumour-induced osteomalacia.

Intracranial Phosphaturic Mesenchymal Tumors: A Systematic Literature Review of a Rare Entity

BACKGROUND

Phosphaturic Mesenchymal Tumors (PMTs) are rare mesenchymal neoplasms known for producing Tumor-induced Osteomalacia (TIO). TIO is an uncommon paraneoplastic syndrome characterized by radiographic evidence of inadequate bone mineralization and analytical abnormalites.

METHODS

We sought to present a case of TIO caused by skull base PMT with intracranial extension, manifesting with pain, progressive weakness, and multiple bone fractures. Furthermore, a systematic review was performed, following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. A search was conducted in PubMed database with title/abstract keywords "Phosphaturic mesenchymal tumor" and "Osteomalacia." Search results were reviewed looking for intracranial or skull base tumors.

RESULTS

Our systematic review included 29 reported cases of intracranial PMT. In the reviewed cases there was a significative female predominance with 22 cases (75,86%). Osteomalacia was presented in 25 cases (86,20%). Bone fractures were present in 10 cases (34,48%). The most common site of involvement was the anterior cranial fossa in 14 cases (48,27%). Surgery was performed in 27 cases (93,10%) with previous tumor embolization in 4 cases (13,79%). Total recovery of the presenting symptoms in the first year was achieved in 21 cases (72,41%). Recurrence of the disease was described in 6 cases (25%).

CONCLUSIONS

Skull base PMTs with intracranial extension are extremely rare tumors. Most patients are middle-aged adults with a PMT predominantly located in anterior cranial fossa. Surgery is the current treatment of choice with optimal outcome at 1-year follow-up, although recurrence could be present in almost 25% of the cases.

Unusual presentation of tumor-induced osteomalacia mismanaged due to misdiagnosis: A literature review based on a case report

Key Clinical Message

Tumor-induced osteomalacia is a rare but potentially serious disease with nonspecific misguiding manifestations that can result in a wrong diagnosis and being treated for rheumatologic or other similar diseases. In patients with unexpected fractures, resistant musculoskeletal pains, and hypophosphatemia, this diagnosis should be considered by the physicians and approached through a complete history taking, physical exam laboratory, and radiologic evaluation to give the opportunity of on-time treatment to the patient.

Abstract

Tumor-induced osteomalacia (TIO) is an uncommon mesenchymal tumor that results in disproportionate phosphorus excretion, primarily leading to bone-related symptoms. Laboratory, imaging, and histopathological evaluation can confirm this pathologic condition. In this case, we present the history and subsequent clinical parts of a 50-year-old woman who presented with an unusual presentation of generalized musculoskeletal pains and a right ankle mass. Her disease was diagnosed with multidisciplinary evaluation and was approached by a surgical treatment. The patient was treated with total resection of the tumor, which led to complete resolution of musculoskeletal and metabolic abnormalities, which were resolved following total tumor resection. TIO is a paraneoplastic disease that results in abnormal secretion of phosphatonins, particularly fibroblast growth factor 23 (FGF23). This can cause hypophosphatemia, hyperparathyroidism, lower bone density, and increased risk of pathologic fractures. These tumors are mostly cured by surgical ± radiotherapy. The present study aims to provide insight into the fact that a TIO diagnosis is not always straightforward. However, in suspicious cases such as unexplained hypophosphatemia, it should be considered to prevent delayed diagnosis of the progressive pathology. The earlier treatment can prevent several complications and reduce the risk of mortality.

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.

Unusual phosphaturic mesenchymal tumor mimicking osteoid osteoma

Phosphaturic mesenchymal tumor is a rare tumor characterized by paraneoplastic osteomalacia. The diagnosis is often delayed because of nonspecific symptoms and difficulty to localize the tumor. In this study we report a case of PMT of the left femur detected by Ga-68-DOTATATE PET-CT with radiological features mimicking osteoid osteoma. We report a 31-year-old female patient who presented to our hospital for evaluation due to progressive bone pain and muscle weakness. Her laboratory data showed hypophosphatemia and increased fibroblast growth factor 23 (FGF-23) together with reduced bone mineral density on bone densitometry. The diagnosis of PMT was suspected and the tumor was identified on Ga-68-DOTATATE PET-CT as a focal uptake in a lucent lesion of the left femoral head with a central sclerotic dot mimicking a nidus as seen in osteoid osteoma. The lesion was treated with percutaneous radiofrequency ablation. Laboratory tests and bone densitometry rapidly improved post-treatment. The present case emphasizes the difficulty to diagnose PMT due to its nonspecific biochemical and clinical presentation and the relevance of functional imaging for locating these tumors despite different radiological presentation.

Tumour induced osteopenia due to phosphaturic mesenchymal sinonasal tumour presenting with delayed onset insufficiency fractures

We present a case of a 48-year-old female who presented with epistaxis. Magnetic resonance imaging (MRI) revealed a mass within the left nasal cavity which was revealed to be a phosphaturic mesenchymal sinonasal tumour. The patient defaulted treatment at this stage and later re-presented with pelvic and groin pain for which plain radiographs and computed tomography (CT) scan demonstrated diffuse osteopenia and multiple pelvic fractures of varying ages. MRI of the pelvis and both thighs revealed abnormal marrow signal of the bones and confirmed the presence of pelvic fractures. Multiple pseudo-fractures were seen at both femurs and scapula. The radiological findings along with abnormal biochemical markers were attributed to the paraneoplastic entity of tumour induced osteomalacia, in the context of unresected phosphaturic mesenchymal tumour. The tumour was resected, and patient showed complete reversal of the associated biochemical abnormalities. This case exemplifies that with early identification and complete resection of the causative tumour, the prognosis is excellent.

Imaging characteristics of phosphaturic mesenchymal tumors

BACKGROUND

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome associated with phosphaturic mesenchymal tumors (PMTs). Localization of the causative tumor in these cases is an arduous task since the culprit lesions are usually small, slow-growing, and can be located almost anywhere from head to toe.

PURPOSE

To describe the morphological characteristics of histologically proven PMTs on various radiological modalities.

MATERIAL AND METHODS

After institutional ethical approval, this retrospective study analyzed 20 cases with a histopathological evidence of PMT. Various imaging characteristics of the tumors on available computed tomography (CT) and magnetic resonance imaging (MRI) scans were evaluated. Descriptive statistical analyses were conducted.

RESULTS

The tumors were located in diverse locations: lower extremities (n = 10); head and neck (n = 5); vertebral column (n = 3); pelvis (n = 1); and upper extremities (n = 1). Bone lesions seen on CT had variable morphology: sclerotic (n = 3/8, 37.5%); lytic (n = 3/8, 37.5%), and both lytic and sclerotic (n = 2/8, 25%) with presence of narrow zone of transition in all cases (n = 8/8) and amorphous internal matrix calcifications in 25% of cases (n = 2/8). Of the tumors, 68.4% (n = 13/19) were hypointense on T1 and all of them showed hyperintense signal on T2-weighted and STIR images (n = 19/19) and contrast enhancement (n = 16/16). Of the tumors, 66.7% (n = 6/9) showed restricted diffusion. DOTANOC PET/CT showed tumor uptake in all cases (n = 8/8).

CONCLUSION

PMTs may have variable and non-specific tumor appearances on various imaging modalities. However, in an appropriate clinical scenario and a background of suggestive biochemical work-up, the radiologist should keep a high index of suspicion.

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.

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.

Diagnosis and surgical treatment of tumor-induced osteomalacia—a literature review and a case report

Background

Tumor-induced osteomalacia (TIO) is a rare condition with fewer than 500 cases reported in the literature although described. Phosphaturic mesenchymal tumor (PMT) is often unrecognized cause of hypophosphatemia. This case report aims to highlight such a rare association which warrants clinical and radiologist attention.

Case

A 51-year-old man had pain in his feet 2 years prior to the most recent presentation in our clinic. The patient experienced increasingly severe body aches and pain, which affected the feet, hips, knees, ribs, waist, and shoulders. MRI and CT led to the diagnosis of multiple insufficiency fractures. Laboratory tests showed that inorganic phosphate (IP) levels had decreased to 0.52 mmol/L(0.81–1.45 mmol/L), while alkaline phosphatase (ALP) had increased to 216 U/L(38.0–126.0 U/L). Positron emission tomography computed tomography showed tumor-derived hypophosphate osteomalacia of the right iliac wing; surgical resection was performed. markers of bone metabolism and bone density returned normal postoperative, after 9 months follow-up.

Conclusion

The possibility of tumor-induced osteomalacia should be considered if unexplained joint pain, decreased bone mineral density, increased ALP and insufficiency fractures, and no similar family history are found in adult patients. Surgical resection of the tumor is the key to the treatment.

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.

Challenges in the management of tumor-induced osteomalacia (TIO)

Tumor-induced osteomalacia (TIO), also known as oncogenic osteomalacia, is a rare acquired paraneoplastic disease, which is challenging to diagnose and treat. TIO is characterized by hypophosphatemia resulting from excess levels of tumor-secreted fibroblast growth factor 23 (FGF23), one of the key physiological regulators of phosphate metabolism. Elevated FGF23 results in renal phosphate wasting and compromised vitamin D activation, ultimately resulting in osteomalacia. Patients typically present with progressive and non-specific symptoms, including bone pain, multiple pathological fractures, and progressive muscle weakness. Diagnosis is often delayed or missed due to the non-specific nature of complaints and lack of disease awareness. Additionally, the disease-causing tumour is often difficult to detect and localize because they are often small, lack localizing symptoms and signs, and dwell in widely variable anatomical locations. Measuring serum/urine phosphate should be an inherent diagnostic component when assessing otherwise unexplained osteomalacia, fractures and weakness. In cases of hypophosphatemia with inappropriate (sustained) phosphaturia and inappropriately normal or frankly low 1,25-dihydroxy vitamin D, differentiation of the potential causes of renal phosphate wasting should include measurement of FGF23, and TIO should be considered. While patients experience severe disability without treatment, complete excision of the tumour is typically curative and results in a dramatic reversal of symptoms. Two additional key current unmet needs in optimizing TIO management are: (1 and 2) the considerable delay in diagnosis and consequent delay between the onset of symptoms and surgical resection; and (2) alternative management. These may be addressed by raising awareness of TIO, and taking into consideration the accessibility and variability of different healthcare infrastructures. By recognizing the challenges associated with the diagnosis and treatment of TIO and by applying a stepwise approach with clear clinical practice guidelines, patient care and outcomes will be improved in the future.

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.

Extended Whole-body Ga-68 DOTATATE PET-CT in evaluating Tumour-Induced Osteomalacia: Case report and review of literature

Tumour-induced osteomalacia is a rare paraneoplastic syndrome that manifests as chronic hypophosphataemia, non-specific bone pain and muscle weakness. It is generally caused by phosphaturic mesenchymal tumour (PMT), which is uncommonly associated with synchronous tumours. However, diagnosis is often delayed for several years due to the rarity, indolent growing nature and non-specific symptoms of the disease, often resulting in an overlook by clinicians during assessments. The patient initially presented with hypophosphataemia and generalised skeletal pain with multiple atraumatic fractures. Blood tests revealed serum calcium levels at the upper limit and extremely low inorganic phosphate levels. Herein, we report a case where two synchronous PMTs from two different sites were detected by 'extended' whole-body Ga-68 DOTATATE PET-CT, leading to remission of the disease after complete surgical removal. Early detection and diagnosis of PMT neoplasm is crucial, as complete surgical resection of this tumour is the only definitive treatment currently known. Upon excision, this curable disease will result in complete resolution of symptoms and blood parameters, leading to remission of the disease which significantly improves the patient's quality of life. PMT often over-expresses somatostatin receptors (SSTR), predominantly subtype 2A, and Ga-68 DOTATATE PET-CT is a selective SSTR imaging that targets this characteristic over-expression in these tumours. The high diagnostic accuracy of Ga-68 DOTATATE PET-CT should be the primary imaging modality for full evaluation of this disease.

Diagnostic utility of Ga-68 DOTA-SSTR and F-18 FDG PET/CT in the detection of culprit tumours causing osteomalacia: a systematic review and meta-analysis

BACKGROUND

Tumour-induced osteomalacia (TIO) or oncogenic osteomalacia is a rare variant of paraneoplastic syndrome secondary to a small benign phosphaturic mesenchymal tumour that secretes phosphaturic substances. Complete tumour excision is often curative. However, the localization of these offending tumours has always remained a challenge because of their small size, slow-growing nature, and presence in atypical locations. We performed a systemic review and meta-analysis on the sensitivity and specificity of F-18 FDG PET/CT and Ga-68 DOTA-SSTR PET/CT to detect tumours causing osteomalacia.

METHODS

Pub Med, SCOPUS, the Cochrane Library and Web of Science were searched for articles on F-18 FDG and Ga-68 DOTA-SSTR PET/CT in the detection of culprit tumours in TIO till September 2020. Both retrospective and prospective studies having three or more patients were included. The methodological quality of included studies was assessed using the Revised Tool for the Quality Assessment of Diagnostic Accuracy Studies-2 checklist. A random-effect model was used for the statistical pooling of sensitivity and specificity. Pooled data were presented with 95% confidence intervals (95% CI) and displayed using Forest plots. Heterogeneity was expressed using the I2 statistic.

RESULTS

The pooled sensitivity of Ga-68 DOTA-SSTR PET/CT in detecting the culprit tumour derived from all included studies is 86% (95% CI: 79-91%). There is moderate statistical heterogeneity among the included studies (I2 = 72.7%). The pooled sensitivity of F-18 FDG PET/CT in detecting the offending tumour derived from all included studies is 73% (95% CI: 61-84%) with moderate statistical heterogeneity among the included studies (I2 = 45.4%).

CONCLUSION

In the detection of offending tumours in TIO, Ga-68 DOTA-SSTR PET/CT has better sensitivity than F-18 FDG PET/CT and should be used as first-line imaging modality due to very high sensitivity.

Can conventional clinical chemistry tests help doctors in the monitoring of oncology patients?

The use of laboratory assays in the diagnostic care of oncology patients can markedly increase the efficacy of cancer treatments. Many cancer-specific biomarker assays have been developed. However, the use of these has some limitations due to their cost. Moreover, not every diagnostic laboratory can perform a complete set of these assays. On the other hand, the smart use of conventional clinical chemistry tests could improve the management of cancer. They could be especially valuable tools in the long-term care of patients with a verified diagnosis. In this review, we discuss the utilization of the conventional clinical chemistry assays for the diagnosis, monitoring and prognosis of various oncological diseases. The use of conventional blood tests to assess the levels of chemical elements, metabolites and proteins (including enzymatic activity measurements) in the care of oncology patients is discussed. We have shown that some clinical chemistry assays could be used in the management of distinct kinds of cancer.

Tumor-Induced Osteomalacia

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by tumoral production of fibroblast growth factor 23 (FGF23). The hallmark biochemical features include hypophosphatemia due to renal phosphate wasting, inappropriately normal or frankly low 1,25-dihydroxy-vitamin D, and inappropriately normal or elevated FGF23. TIO is caused by typically small, slow growing, benign phosphaturic mesenchymal tumors (PMTs) that are located almost anywhere in the body from the skull to the feet, in soft tissue or bone. The recent identification of fusion genes in a significant subset of PMTs has provided important insights into PMT tumorigenesis. Although management of this disease may seem straightforward, considering that complete resection of the tumor leads to its cure, locating these often-tiny tumors is frequently a challenge. For this purpose, a stepwise, systematic approach is required. It starts with thorough medical history and physical examination, followed by functional imaging, and confirmation of identified lesions by anatomical imaging. If the tumor resection is not possible, medical therapy with phosphate and active vitamin D is indicated. Novel therapeutic approaches include image-guided tumor ablation and medical treatment with the anti-FGF23 antibody burosumab or the pan-FGFR tyrosine kinase inhibitor, BGJ398/infigratinib. Great progress has been made in the diagnosis and treatment of TIO, and more is likely to come, turning this challenging, debilitating disease into a gratifying cure for patients and their providers.

Peptide Receptor Radionuclide Therapy for a Phosphaturic Mesenchymal Tumor

Tumor-induced osteomalacia is a very rare paraneoplastic syndrome. It can be caused by phosphaturic mesenchymal tumor (PMT), a generally benign tumor that produces fibroblast growth factor 23 (FGF-23), which can cause a severe renal phosphate wasting syndrome. Upon complete surgical removal of the tumor, FGF-23 normalizes and the osteomalacia is cured. In cases in which surgery is not feasible, radiofrequency ablation (RFA) is the treatment of choice. We describe a case with a PMT situated in the sacrum, in close proximity to the sacral plexus. Both surgery and RFA were considered potentially nerve damaging. Since the tumor showed expression of somatostatin receptors, we opted for a peptide receptor radionuclide therapy (PRRT) with ¹⁷⁷Lu-DOTATOC. However, the therapy did not show the expected success, since the FGF-23 level had even temporarily increased. The patient was then successfully treated with RFA. A partial remission of the tumor was achieved and FGF-23 levels nearly normalized. Despite some severe neurological side effects, the patient showed a remarkable clinical improvement, with no symptoms of osteomalacia within a few weeks.

Hypophosphatemic Hypovitaminosis D Induces Osteomalacia in the Adult Female Rat

Osteomalacia is a bone-demineralizing disease of adulthood, often caused by hypovitaminosis D. Current animal models of the disease mimic osteomalacia as a consequence of gastric bypass or toxic exposure to metals, but a relevant model of diet-induced osteomalacia is lacking. For that purpose, 7-month-old female Sprague Dawley rats were randomly assigned into 2 weight-stratified groups and maintained for 4 months on synthetic diets containing negligible or normal levels of vitamin D. The dietary regimen resulted in vitamin D deficiency as measured by 25-hydroxyvitamin D serum levels; however, hypovitaminosis D per se did not affect biomarkers of calcium metabolism and bone turnover, nor did it result in increased osteoid. Thus, vitamin D depletion through the diet was found to be insufficient to induce an osteomalacia-like phenotype in the adult rat. After 4 months, the phosphate content of the vitamin D-depleted diet had decreased to 0.16% (calcium:phosphorus ratio of 5.85), resulting in an osteomalacic-like condition (trabecular osteoid surface/bone surface constituted 33%; CI, 26-40). The diet change also affected both metabolic and bone turnover biomarkers, including significantly suppressing serum fibroblast growth factor 23. Furthermore, decreased dietary phosphate in a vitamin D-depleted diet led to microarchitectural changes of trabecular and cortical bone, lower bone mass density, lower bone mass content and decreased bone strength, all indicating reduced bone quality. Taken together, our results show that osteomalacia can be induced in the adult female rat by depleting vitamin D and lowering phosphate content in the diet.

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.

[Osteomalacia-Clinical aspects, diagnostics and treatment]

Osteomalacia is a bone disease caused by impaired skeletal mineralization. Vitamin D dependent types have to be distinguished from hypophosphatemic forms. Typical signs and symptoms include diffuse bone pain, muscle weakness and fragility fractures. The fracture pattern in osteomalacia is typically different from that of osteoporosis. Fragility fractures of the pelvis, sacrum, distal parts of the foot, proximal tibia and ribs are indicators for osteomalacia, whereas femoral neck and vertebral fractures (wedged vertebra, fish vertebra, vertebra plana and cover plate impression fractures) are typical for osteoporosis. Unspecific clinical features may be the reason for a delayed diagnosis. The correct classification of the complaint is dependent on the knowledge of the pathophysiology of osteomalacia and performance of additional bone-specific examinations. Determination of specific laboratory parameters should follow a rational algorithm, supplemented by imaging methods and a bone biopsy.

A Rare Case of Phosphaturic Tumor/Oncogenic Osteomalacia - Diagnostic Challenges and Management Algorithm

Introduction

Oncogenic osteomalacia is a rare paraneoplastic syndrome of acquired hypophosphatemic osteomalacia, resulting from a deficit in renal tubular phosphate reabsorption, in which fibroblast growth factor 23 seems to be implicated.

Case Report

A 42-year-old male presented with complaints of low back pain for the past 4 years and inability to walk for the past 3 years. Blood investigations showed hypophosphatemia and elevated serum alkaline phosphatase. Radiographs and magnetic resonance imaging revealed features of osteomalacia. DOTONAC PET-computed tomography (CT) showed a lesion in the greater trochanter suggestive of a phosphaturic mesenchymal tumor. CT-guided biopsy of the lesion was done which confirmed the diagnosis. The tumor was resected by intralesional methods (burring and cementation) with correction of hypophosphatemia by oral phosphorus supplementation. Patient clinically improved and was able to walk with support at the time of discharge.

Conclusion

Phosphaturic tumor was localized to be in the posterior aspect of the right greater trochanter. To find the tumor was a major diagnostic challenge involving various diagnostic modalities. The occurrence of such a condition is rare and it may take even years to correctly diagnose the disease.

Oncogenic Osteomalacia with Elevated Fibroblast Growth Factor 23: A Rare Case of Paranasal Sinus Tumor Onset

Tumor-induced osteomalacia, also known as oncogenic osteomalacia, is a rare, acquired paraneoplastic disease characterized by hypophosphatemia and renal phosphate wasting.

We report on the case of a 52-year-old-man admitted to our hospital for bone and muscular pains and difficulty in walking. He underwent a computed tomography (CT) scan of the legs that documented fractures in the right tibia, femur, and fifth metatarsus. Laboratory findings showed hypophosphatemia and elevated levels of parathyroid hormone (PTH). The first diagnosis was osteomalacia, treated with calcium and vitamin D, without any benefit. So he underwent a whole body CT scan, showing a small expansive lesion occupying the left frontal sinus. Furthermore, we found high serum levels of fibroblast growth factor 23 (FGF23) using the enzyme-linked immune sorbent assay (ELISA) assay. The patient underwent endoscopic surgical resection of the frontal tumor with complete clinical remission and the histopathological diagnosis of an ossifying fibromyxoid tumor.

This is a rare case of oncogenic osteomalacia due to a paranasal sinus tumor. The main symptoms are not associated with nasal sinus involvement but with over-expressed FGF23. To conclude, physicians should never underestimate the chance of paraneoplastic syndrome in the head and neck district, even if such an occurrence is uncommon in this location. The clinical symptoms may be aspecific and not related to nose problems, making the differential diagnosis very difficult.

Tumor-induced osteomalacia: experience from three tertiary care centers in India

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by recalcitrant hypophosphatemia. Reports from the Indian subcontinent are scarce, with most being single center experiences involving few patients. Herein, we conducted a retrospective analysis of 30 patients of TIO diagnosed at three tertiary care hospitals in India. Patients with persistent hypophosphatemia (despite correction of hypovitaminosis D), normocalcemia, elevated alkaline phosphatase, low TmP/GFR and elevated or 'inappropriately normal' FGF23 levels were labeled as having TIO. They were sequentially subjected to functional followed by anatomical imaging. Patients with a well-localized tumor underwent excision; others were put on phosphorous and calcitriol supplementation. The mean age at presentation was 39.6 years with female:male ratio of 3:2. Bone pain (83.3%) and proximal myopathy (70%) were the chief complaints; 40% of cases had fractures. The mean delay in diagnosis was 3.8 years. Tumors were clinically detectable in four patients (13.3%). The mean serum phosphate was 0.50 mmol/L with a median serum FGF23 level of 518 RU/mL. Somatostatin receptor-based scintigraphy was found to be superior to FDG-PET in tumor localization. Lower extremities were the most common site of the tumor (72%). Tumor size was positively correlated with serum FGF23 levels. Twenty-two patients underwent tumor resection and 16 of them had phosphaturic mesenchymal tumors. Surgical excision led to cure in 72.7% of patients whereas disease persistence and disease recurrence were seen in 18.2% and 9.1% of cases, respectively. At the last follow-up, serum phosphate in the surgically treated group was significantly higher than in the medically managed group.

Physiological regulation of phosphate by vitamin D, parathyroid hormone (PTH) and phosphate (Pi)

Inorganic phosphate (Pi) is an abundant element in the body and is essential for a wide variety of key biological processes. It plays an essential role in cellular energy metabolism and cell signalling, e.g. adenosine and guanosine triphosphates (ATP, GTP), and in the composition of phospholipid membranes and bone, and is an integral part of DNA and RNA. It is an important buffer in blood and urine and contributes to normal acid-base balance. Given its widespread role in almost every molecular and cellular function, changes in serum Pi levels and balance can have important and untoward effects. Pi homoeostasis is maintained by a counterbalance between dietary Pi absorption by the gut, mobilisation from bone and renal excretion. Approximately 85% of total body Pi is present in bone and only 1% is present as free Pi in extracellular fluids. In humans, extracellular concentrations of inorganic Pi vary between 0.8 and 1.2 mM, and in plasma or serum Pi exists in both its monovalent and divalent forms (H2PO4- and HPO42-). In the intestine, approximately 30% of Pi absorption is vitamin D regulated and dependent. To help maintain Pi balance, reabsorption of filtered Pi along the renal proximal tubule (PT) is via the NaPi-IIa and NaPi-IIc Na+-coupled Pi cotransporters, with a smaller contribution from the PiT-2 transporters. Endocrine factors, including, vitamin D and parathyroid hormone (PTH), as well as newer factors such as fibroblast growth factor (FGF)-23 and its coreceptor α-klotho, are intimately involved in the control of Pi homeostasis. A tight regulation of Pi is critical, since hyperphosphataemia is associated with increased cardiovascular morbidity in chronic kidney disease (CKD) and hypophosphataemia with rickets and growth retardation. This short review considers the control of Pi balance by vitamin D, PTH and Pi itself, with an emphasis on the insights gained from human genetic disorders and genetically modified mouse models.

Phosphate wasting disorders in adults

A cause of hypophosphatemia is phosphate wasting disorders. Knowledge concerning mechanisms involved in phosphate wasting disorders has greatly increased in the last decade by the identification of phosphatonins, among them FGF-23. FGF-23 is a primarily bone derived factor decreasing renal tubular reabsorption of phosphate and the synthesis of calcitriol. Currently, pharmacological treatment of these disorders offers limited efficacy and is potentially associated to gastrointestinal, renal, and parathyroid complications; therefore, efforts have been directed toward newer pharmacological strategies that target the FGF-23 pathway. This review focuses on phosphate metabolism, its main regulators, and phosphate wasting disorders in adults, highlighting the main issues related to diagnosis and current and new potential treatments.

Successful Localization Using 68Ga-DOTATOC PET/CT of a Phosphaturic Mesenchymal Tumor Causing Osteomalacia in a Patient with Concurrent Follicular Lymphoma

Diagnosing tumor-induced osteomalacia is often challenging because conventional imaging modalities may fail to locate the responsible tumor. This report describes the ability of ⁶⁸Ga-DOTATOC PET/CT to successfully distinguish between the responsible phosphaturic mesenchymal tumor and concurrent lymphoma lesions. A 52-year-old man with bone pain for several years was diagnosed with a vitamin D-resistant hypophosphatemic osteomalacia. Whole body ¹⁸F-FDG PET/CT revealed multiple enlarged hypermetabolic lymph nodes in his bilateral cervical, axillary, mediastinal, abdominal, pelvic, and inguinal regions. Core needle biopsy of the right cervical lymph node confirmed the diagnosis of follicular lymphoma. However, lymphoma was not considered the cause of osteomalacia. ⁶⁸Ga-DOTATOC PET/CT before chemotherapy showed a small nodule with intensely increased uptake in the right inguinal region, which was distinguished from the other enlarged lymph nodes. The nodule was surgically removed and histopathologically consistent with phosphaturic mesenchymal tumor. After surgery, the patient's serum phosphorus and alkaline phosphatase levels normalized without nutritional supplement.

Hypophosphataemia: an important cause of collapse

We present a case of a 44-year-old man, civil servant, who presented to the emergency department (ED) following an episode of collapse. He was usually fit and well and while at work he had developed a headache with pins and needles over his face and subsequently collapsed. On arrival to ED, he had a Glasgow Coma Scale (GCS) of 4/15. There was no history of note apart from being prescribed citalopram for depression. Laboratory investigations revealed severe hypophosphataemia (phosphate 0.19 mmol/L) and no other electrolyte abnormality. He was commenced on intravenous phosphate and his GCS improved to 15 within 4 hours. Further investigations revealed no cause for his severe hypophosphataemia and repeat bloods in clinic follow-up showed a normal phosphate level.

Phosphaturic mesenchymal tumor, an unusual localization in head and neck

Phosphaturic mesenchymal tumor (PMT) is a rare mesenchymal neoplasm associated with tumor-induced osteomalacia involving bone and soft tissue that produces paraneoplastic hypophosphatemic osteomalacia. The common physiologic defect in this conditions involves an impairment in renal tubular phosphate reabsorption with a downregulation of renal 1α-hydroxylase activity, while calcium metabolism remains essentially unaffected. Microscopic features consist of spindle cells, multinucleated giant cells and calcifications embedded in a chondromyxoid matrix with variable cellularity and prominent vascularity. Approximately 95% of PMTs involve the extremities and appendicular skeleton, with only 5% occurring in the head and neck region. Localization in the head and neck is pretty uncommon, nose and paranasal sinuses are preferentially affected. Due to its rarity, the purpose of the study was to report a new case of PMT whose locations in temporomandibular joint was never reported in literature.

Hypophosphatemia, Severe Bone Pain, Gait Disturbance, and Fatigue Fractures After Iron Substitution in Inflammatory Bowel Disease: A Case Report

Intravenous infusions of different iron formulations are recognized as a cause of hypophosphatemia. Chronic hypophosphatemia can alter bone metabolism and bone material structure. As a consequence, osteomalacia may develop and lead to bone fragility. Herein, we report a patient with Crohn's disease presenting with persistent hypophosphatemia and insufficiency fractures while receiving regular iron infusions due to chronic gastrointestinal bleeding. Previously, the patient regularly received vitamin D and also zoledronic acid. The patient underwent bone biopsy of the iliac crest that showed typical signs of osteomalacia with dramatically increased osteoid volume and decreased bone formation. Analysis of the bone mineralization density distribution (BMDD) revealed a more complex picture: On the one hand, there was a shift to higher matrix mineralization, presumably owing to low bone turnover; on the other hand, a broadening of the BMDD indicating more heterogeneous mineralization due to osteomalacia was also evident. This is the first report on changes of bone histomorphometry and bone matrix mineralization in iron-induced osteomalacia. © 2017 American Society for Bone and Mineral Research.

The Foot That Broke Both Hips: A Case Report and Literature Review of Tumor-Induced Osteomalacia

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by hypophosphatemia and clinical symptoms of osteomalacia. Only discussed as case reports, there is still limited knowledge of this condition as a potentially curable cause of osteomalacia among clinicians and pathologists. In this article, we present a case of tumor-induced osteomalacia in a 59-year-old gentleman followed by an up-to-date review of the existing literature on TIO.

Treatment and outcomes of tumor-induced osteomalacia associated with phosphaturic mesenchymal tumors: retrospective review of 12 patients

Background

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by severe hypophosphatemia and osteomalacia. Nonspecific symptoms make the diagnosis elusive. In addition, locating the responsible tumor(s) is challenging. The aim of this study was to investigate the clinical management and outcomes of TIO.

Methods

The clinical features, diagnostic procedures, treatment, and outcomes of 12 patients were reviewed retrospectively.

Results

The cohort comprised six men and six women (mean age 45.5 ± 9.9 years, range 23–61 years). The mean duration of disease was 3.7 ± 2.6 years. All patients manifested progressive bone pain, muscle weakness, and/or difficulty walking. Serum phosphorus concentrations were low in all patients (mean 0.42 ± 0.12 mmol/L). Technetium-99m octreotide scintigraphy was performed in 11 patients and showed lesions in the right distal femur, left femoral head, and right tibial plateau, respectively, in three patients. Magnetic resonance imaging (MRI) was negative for lesions in one patient. Two patients underwent biopsies that showed negative histopathology. Two patients, at 2 years and 8 months, respectively, after having negative technetium-99m octreotide studies, underwent ¹⁸F–fluorodeoxyglucose positron emission tomography/computed tomography (CT), which revealed lesions in the sacrum and soft tissue of the left palm, respectively. One tumor was detected by CT and MRI. Overall, lesion sites were the head (two patients, 16.7%), thoracic and lumbar region (two, 16.7%), pelvis (three, 25%), lower limbs (four, 33.3%), and upper limbs (one, 8.3%). All patients underwent surgery, and histopathology showed phosphaturic mesenchymal tumors in each. Postoperatively, serum phosphorus concentrations normalized within 2–7 days in 11 patients. With follow-ups of 1–41 months, surgery was effective in 10 patients. One patient developed local recurrence and another had metastases.

Conclusions

Locating tumors responsible for tumor-induced osteomalacia is often challenging. Although complete tumor resection confers a good prognosis in most patients, surveillance for recurrence and metastasis is necessary. Before surgery or when surgery is not indicated, oral phosphate can alleviate symptoms and metabolic imbalance.

Electronic supplementary material

The online version of this article (10.1186/s12891-017-1756-1) contains supplementary material, which is available to authorized users.

The diagnostic dilemma of tumor induced osteomalacia: a retrospective analysis of 144 cases

Diagnostic delay of tumor induced osteomalacia (TIO) is common in clinic practice. To investigate the diagnostic condition of TIO in China and raise clinicians' awareness of TIO, we retrospectively analyzed clinical manifestations, biochemical features, and specially evaluated missed diagnoses and misdiagnoses among 144 TIO patients from Peking Union Medical College Hospital during December 1982 to December 2014. Clinical presentations of TIO mainly included bone pain, difficulty in walking, pathological fractures, muscle weakness, and height loss. TIO patients demonstrated hypophosphatemia (0.48±0.13 mmol/L), elevated serum alkaline phosphatase (277.9±152.6 U/L), reduced tubular maximum for phosphorus/glomerular filtration rate (0.39±0.14) and markedly elevated serum fibroblast growth factor 23 (FGF23) (median level 302.9 pg/mL). The average time from onset to a correct diagnosis was 2.9±2.3 years while the mean duration from onset to tumor resection was 5.4±4.2 years. The initial misdiagnosis rate was 95.1% (137/144) and 240 case-times of misdiagnoses occurred among the 144 cases. The most frequent misdiagnoses were intervertebral disc herniation, spondyloarthritis (including ankylosing spondylitis) and osteoporosis. A total of 43.1% (62/144) cases with hypophosphatemia presented on their laboratory sheets were neglected and missed diagnosed. Our study showed that TIO was frequently misdiagnosed and missed diagnosed due to its rarity, insidious onset, nonspecific clinical manifestations and clinicians' poor recognition. It is necessary to test serum phosphorus in patients with musculoskeletal symptoms and difficulty in walking. The measurement of serum FGF23 is rather valuable. Once hypophosphatemia is discovered, TIO should be suspected and it is highly recommended to search for tumors and perform curative surgery.

Coupling between phosphate and calcium homeostasis: a mathematical model

We developed a mathematical model of calcium (Ca) and phosphate (PO₄) homeostasis in the rat to elucidate the hormonal mechanisms that underlie the regulation of Ca and PO₄ balance. The model represents the exchanges of Ca and PO₄ between the intestine, plasma, kidneys, bone, and the intracellular compartment, and the formation of Ca-PO₄-fetuin-A complexes. It accounts for the regulation of these fluxes by parathyroid hormone (PTH), vitamin D₃, fibroblast growth factor 23, and Ca²⁺-sensing receptors. Our results suggest that the Ca and PO₄ homeostatic systems are robust enough to handle small perturbations in the production rate of either PTH or vitamin D₃ The model predicts that large perturbations in PTH or vitamin D₃ synthesis have a greater impact on the plasma concentration of Ca²⁺ ([Ca²⁺]_p) than on that of PO₄ ([PO₄]_p); due to negative feedback loops, [PO₄]_p does not consistently increase when the production rate of PTH or vitamin D₃ is decreased. Our results also suggest that, following a large PO₄ infusion, the rapidly exchangeable pool in bone acts as a fast, transient storage PO₄ compartment (on the order of minutes), whereas the intracellular pool is able to store greater amounts of PO₄ over several hours. Moreover, a large PO₄ infusion rapidly lowers [Ca²⁺]_p owing to the formation of CaPO₄ complexes. A large Ca infusion, however, has a small impact on [PO₄]_p, since a significant fraction of Ca binds to albumin. This mathematical model is the first to include all major regulatory factors of Ca and PO₄ homeostasis.

Tumor-induced Osteomalacia: A Sherlock Holmes Approach to Diagnosis and Management

Tumor-induced osteomalacia (TIO) is a subtype of paraneoplastic syndrome associated with hypophosphatemia due to renal phosphate wasting in adults. The humoral factor responsible for clinical picture known as fibroblast growth factor 23 (FGF23) is most often secreted by benign yet elusive mesenchymal tumors, difficult to localize, access, and excise completely; rarely, they are multiple and malignant. Paradoxical inappropriately normal or low levels of 1,25-dihydroxyvitamin D in the setting of hypophosphatemia is due to suppressive effect of FGF23. The following case report describes a 31-year-old male with symptoms of multiple fractures and severe muscle weakness, hypophosphatemia with elevated tubular maximum reabsorption of phosphate/glomerular filtration rate with low active Vitamin D, prompted assay for C-terminal FGF23, which was elevated multifold. The tumor was localized with whole body 68-Gadolinium DOTANOC positron emission tomography-computed tomography fusion scan in the left nasal cavity with ipsilateral maxillary antrum. It was excised through transnasal approach and found to be mesenchymal tumor on histopathology. At 1 week of follow-up, serum phosphate became normalized without supplementation. The patient is in follow-up for further measurement of FGF23 level and signs of recurrence. Because the occurrence of such a condition is rare and most often misdiagnosed or mismanaged for years, it is important to recognize this condition in differential diagnosis as potential curative surgical option is a reality.

Tumour-induced osteomalacia

Tumour-induced osteomalacia (TIO), also known as oncogenic osteomalacia, is a rare paraneoplastic disorder caused by tumours that secrete fibroblast growth factor 23 (FGF23). Owing to the role of FGF23 in renal phosphate handling and vitamin D synthesis, TIO is characterized by decreased renal tubular reabsorption of phosphate, by hypophosphataemia and by low levels of active vitamin D. Chronic hypophosphataemia ultimately results in osteomalacia (that is, inadequate bone mineralization). The diagnosis of TIO is usually suspected when serum phosphate levels are chronically low in the setting of bone pain, fragility fractures and muscle weakness. Locating the offending tumour can be very difficult, as the tumour is often very small and can be anywhere in the body. Surgical removal of the tumour is the only definitive treatment. When the tumour cannot be located or when complete resection is not possible, medical treatment with phosphate salts or active vitamin D is necessary. One of the most promising emerging treatments for unresectable tumours that cause TIO is the anti-FGF23 monoclonal antibody KRN23. The recent identification of a fusion of fibronectin and fibroblast growth factor receptor 1 (FGFR1) as a molecular driver in some tumours not only sheds light on the pathophysiology of TIO but also opens the door to a better understanding of the transcription, translocation, post-translational modification and secretion of FGF23, as well as suggesting approaches to targeted therapy. Further study will reveal if the FGFR1 pathway is also involved in tumours that do not harbour the translocation.

Paraneoplastic endocrine syndromes

The majority of neoplasms are responsible for symptoms caused by mass effects to surrounding tissues and/or through the development of metastases. However, occasionally neoplasms, with or without endocrine differentiation, acquire the ability to secrete a variety of bioactive substances or induce immune cross-reactivity with the normal tissues that can lead to the development of characteristic clinical syndromes. These syndromes are named endocrine paraneoplastic syndromes when the specific secretory components (hormones, peptides or cytokines) are unrelated to the anticipated tissue or organ of origin. Endocrine paraneoplastic syndromes can complicate the patient's clinical course, response to treatment, impact prognosis and even be confused as metastatic spread. These syndromes can precede, occur concomitantly or present at a later stage of tumour development, and along with the secreted substances constitute the biological 'fingerprint' of the tumour. Their detection can facilitate early diagnosis of the underlying neoplasia, monitor response to treatment and/or detect early recurrences following successful initial management. Although when associated with tumours of low malignant potential they usually do not affect long-term outcome, in cases of highly malignant tumours, endocrine paraneoplastic syndromes are usually associated with poorer survival outcomes. Recent medical advances have not only improved our understanding of paraneoplastic syndrome pathogenesis in general but also enhanced their diagnosis and treatment. Yet, given the rarity of endocrine paraneoplastic syndromes, there is a paucity of prospective clinical trials to guide management. The development of well-designed prospective multicentre trials remains a priority in the field in order to fully characterise these syndromes and provide evidence-based diagnostic and therapeutic protocols.

Total hip/knee arthroplasty in the treatment of tumor-induced osteomalacia patients: More than 1 year follow-up

Background

Tumor-induced osteomalacia (TIO) may result in a better prognosis after complete resection of the causative neoplasm. However, tumors located proximal to the articular surface of the metaphysis remain largely uninvestigated.

Methods

A retrospective study of sixteen patients was undertaken to evaluate treatment of tumors with joint arthroplasty and tumor resection. The bone metabolism index, hip/knee joint function, arthroplasty complications and symptoms were followed up for at least 12 months in each patient.

Results

All patients presented with neoplasms situated in the articular surface of the metaphysis, with 13 cases undergoing hip arthroplasty and 3 undergoing knee arthroplasty. Treatment of the tumors with joint arthroplasty and tumor resection significantly and rapidly ameliorate bone metabolism indexes in patients with TIO (p<0.01), with no identified tumor recurrence. The joint function evaluation score was improved in 15 patients (93.75%). Complications in these patients included post-operative pain, joint squeaking and secondary hyperparathyroidism.

Conclusions

Joint arthroplasty that includes tumor-expanding resection appears to be a safe and appropriate method for the treatment of TIO patients with a neoplasm located in the metaphysis proximal to the articular surface.

Level of evidence

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Effective localization in tumor-induced osteomalacia using 68Ga-DOTATOC-PET/CT, venous sampling and 3T-MRI

Summary

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by renal phosphate wasting leading to hypophosphatemia due to excessive actions of fibroblast growth factor 23 (FGF23) produced by the tumors. Although the best way of curing TIO is complete resection, it is usually difficult to detect the culprit tumors by general radiological modalities owing to the size and location of the tumors. We report a case of TIO in which the identification of the tumor by conventional imaging studies was difficult. Nonetheless, a diagnosis was made possible by effective use of multiple modalities. We initially suspected that the tumor existed in the right dorsal aspect of the scapula by ⁶⁸Ga-DOTATOC positron emission tomography/computed tomography (⁶⁸Ga-DOTATOC-PET/CT) and supported the result by systemic venous sampling (SVS). The tumor could also be visualized by 3T-magnetic resonance imaging (MRI), although it was not detected by 1.5T-MRI, and eventually be resected completely. In cases of TIO, a stepwise approach of ⁶⁸Ga-DOTATOC-PET/CT, SVS and 3T-MRI can be effective for confirmation of diagnosis.

Learning points:

Fibroblast Growth Factor 23-Mediated Bone Disease

Fibroblast growth factor 23 (FGF23) is an important regulator of phosphate and vitamin D metabolism and its excessive or insufficient production leads to a wide variety of skeletal disorders. This article reviews the FGF23-α-Klotho signaling pathway, highlighting the latest developments in FGF23 regulation and action, and describes the disorders associated with FGF23 excess or deficiency.

[Small cell lung cancer associated with multiple paraneoplastic syndromes]

We report the case of a patient presenting with multiple severe electrolyte disturbances who was subsequently found to have small cell lung cancer. Upon further evaluation, she demonstrated three distinct paraneoplastic processes, including the syndrome of inappropriate antidiuretic hormone, Fanconi syndrome, and an inappropriate elevation in fibroblast growth factor-23 (FGF23). The patient underwent one round of chemotherapy, but she was found to have progressive disease. After 36 days of hospitalization, the patient made the decision to enter hospice care and later she expired.

Musculoskeletal oncogenic osteomalacia-An experience from a single centre in South India

BACKGROUND

Oncogenic osteomalacia is an acquired form of hypophosphatemic osteomalacia where the tumour resection may lead to cure of the disease. Tumours originating from the musculoskeletal region form an important subgroup of oncogenic osteomalacia.

METHODS

This was a retrospective study conducted at a tertiary care centre in south India where we analyzed the hospital records of all the patients with musculoskeletal oncogenic osteomalacia from January 2010-April 2016.

RESULTS

A total number of 73 patients were diagnosed to have adult onset hypophosphatemic osteomalacia out of which 13 patients (M: F = 6:7; mean age: 45.38 ± 18.23 years) with musculoskeletal oncogenic osteomalacia were included in the study. Common presenting symptoms were bony pains, proximal myopathy and fractures. Mean duration of symptoms from the initial hospital visit was 58.46 ± 64.48 months. The initial mean fibroblast growth factor (FGF) 23 levels being 828.86 ± 113.22 RU/ml (Normal range: 22-91). Imaging modalities used for localization of the tumour: DOTATATE PET/CT (8 patients), FDG PET/CT (3 patients), 1 patient (Both DOTATATE PET/CT and FDG PET/CT) and whole body Tc 99 m Red blood cell (RBC) blood pool scintigraphy (2 patients). 9 patients underwent surgery and all achieved remission. 4 patients denied surgical consent.

CONCLUSION

Musculoskeletal oncogenic osteomalacia is a major subgroup of oncogenic osteomalacia which need more extensive whole body imaging for the localization of the tumour. Surgical excision often leads to remission of the disease.