Four cases of acquired hypophosphataemic ('oncogenic') osteomalacia. Problems of diagnosis, treatment and long-term management

Adult-onset hypophosphatemic osteomalacia as a cause of widespread musculoskeletal pain: A retrospective case series of single center experience

BACKGROUND

Osteomalacia (OM) is frequently confused with various musculoskeletal or other rheumatic diseases, especially in patients with adult-onset widespread musculoskeletal pain because of its low prevalence and non-specific manifestations.

AIM

To facilitate the early diagnosis and etiology-specific treatment of adult-onset hypophosphatemic OM.

METHODS

A retrospective review of medical records was performed to screen adult patients who visited a physiatry locomotive medicine clinic (spine and musculoskeletal pain clinic) primarily presenting with widespread musculoskeletal pain at a single tertiary hospital between January 2011 and December 2019. We enrolled patients with hypophosphatemia, high serum bone-specific alkaline phosphatase levels, and at least one imaging finding suggestive of OM.

RESULTS

Eight patients with adult-onset hypophosphatemic OM were included. The back was the most common site of pain. Proximal dominant symmetric muscle weakness was observed in more than half of the patients. Bone scintigraphy was the most useful imaging modality for diagnosing OM because radiotracer uptake in OM showed characteristic patterns. Six patients were diagnosed with adefovir (ADV)-induced Fanconi syndrome, and the other two patients were diagnosed with tumor-induced OM and light-chain nephropathy, respectively. After phosphorus and vitamin D supplementation and treatment for the underlying etiologies, improvements in pain, muscle strength, and gait were observed in all patients.

CONCLUSION

Mechanical pain characteristics, hypophosphatemia, and distinctive bone scintigraphy patterns are the initial diagnostic indicators of adult-onset hypophosphatemic OM. ADV-induced Fanconi syndrome is the most common etiology of hypophosphatemic OM in hepatitis B virus-endemic countries.

Phosphaturic Mesenchymal Tumors with or without Phosphate Metabolism Derangements

Phosphaturic mesenchymal tumors (PMT) are rare neoplasms, which can give rise to a multifaceted syndrome, otherwise called tumor-induced osteomalacia (TIO). Localizing these tumors is crucial to obtain a cure for the phosphate metabolism derangement, which is often the main cause leading the patient to seek medical help, because of invalidating physical and neuromuscular symptoms. A proportion of these tumors is completely silent and may grow unnoticed, unless they become large enough to produce pain or discomfort. FGF-23 can be produced by several benign or malignant PMTs. The phosphate metabolism, radiology and histology of these rare tumors must be collectively assessed by a multidisciplinary team aimed at curing the disease locally and improving patients' quality of life. This narrative review, authored by multiple specialists of a tertiary care hospital center, will describe endocrine, radiological and histological features of these tumors, as well as present surgical and interventional strategies to manage PMTs.

Persistence and recurrence in tumor-induced osteomalacia: A systematic review of the literature and results from a national survey/case series

PURPOSE

Tumor induced osteomalacia (TIO) is a rare disease of mineral metabolism, whose clinical picture is dominated by hypophosphatemia usually due to an excess of circulating FGF23 produced by small mesenchymal tumors. Data on the real prevalence of the disease are lacking, with the knowledge of the disease mainly relying on case reports and small case series. No estimate is available on the prevalence of uncured TIO.

METHODS

National multi-center, cross-sectional and retrospective study on persistent or recurrent cases of TIO followed in referral centers for bone diseases; systematic review of the published persistent and recurrent cases of TIO. Data from patients consecutively evaluated in referral Italian centers for bone diseases were collected; a PubMed search on persistent, recurrent and unoperable cases of TIO was carried out.

RESULTS

Sixteen patients (mean age at diagnosis 52.5 ± 10.6 years) with persistent (n = 6, 37,5%), recurrent (n = 7, 43.7%) or not operable (n = 3, 18.8%) TIO were described. Delay in diagnosis (2.5 ± 1.3 years) was demonstrated. All patients experienced fragility fractures or pseudofractures and disabling bone and muscle pain. BMD was significantly reduced (mean T-score -2.7 ± 1.7 and -2.7 ± 0.9 at lumbar spine and femoral neck, respectively). Fourteen patients were maintained under therapy with phosphate salts and calcitriol, while in 2 patients therapy with burosumab, an anti-FGF23 antibody, was commenced.

CONCLUSION

A significant number of patients with TIO remain either undiagnosed for tumor localization or tumor recur or persist after surgery. These patients with active disease represent possible candidates for burosumab treatment.

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.

Disorders of Divalent Ions (Magnesium, Calcium, and Phosphorous) in Patients With Cancer

Disorders of the divalent ions (magnesium, calcium, and phosphorous) are frequently encountered in patients with cancer. Of these, hypomagnesemia, hypocalcemia, hypercalcemia, and hypophosphatemia are seen most commonly. These electrolyte disturbances may be related to the underlying malignancy or due to side effects of anticancer therapy. When caused by a paraneoplastic process, these abnormalities may portend a poor prognosis. Importantly, the development of severe electrolyte derangements may be associated with symptoms that negatively impact quality of life, preclude the administration of critical chemotherapeutic agents, or lead to life-threatening complications that require hospitalization and emergent treatment. In accordance, prompt recognition and treatment of these disorders is key to improving outcomes in patients living with cancer. This review will discuss selected derangements of the divalent ions seen in this population, with a focus on paraneoplastic and therapy-associated etiologies.

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.

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.

Tumor induced osteomalacia in head and neck region: single center experience and systematic review

Tumor-induced osteomalacia in the head and neck region remains a challenging diagnosis to manage. Literature pertaining to management and outcome details remains sparse. We describe two cohorts: cohort 1 included seven patients from a single center in Western India with tumors located in paranasal sinuses (n = 3), intracranial (n = 2) and maxilla (n = 2). The unique features from our series is the management of persistent disease with radiation therapy (n = 2) and peptide receptor radionuclide therapy (PRRT) (n = 1). Cohort two has 163 patients identified from 109 publications for systematic review. Paranasal sinuses, mandible, intracranial disease, maxilla and oral cavity, in descending order, are reportedly common tumor sites. Within this cohort, mean age was 46 ± 14 years at presentation with 44.1% having local symptoms. Duration of symptoms varied from 1 to 240 months. Pre-surgery mean serum phosphorus was 1.4 ± 0.4 mg/dL and median FGF-23 levels were 3.6 (IQR:1.8-6.8) times of normal upper limit of normal. Majority (97.5%) were managed primarily with surgical excision; however, primary radiotherapy (n = 2) and surgery combined with radiotherapy (n = 2) were also reported. Twenty patients had persistent disease while nine patients had recurrence, more commonly noted with intracranial and oral cavity tumors. Surgery was the most common second mode of treatment employed succeeded by radiotherapy. Four patients had metastatic disease. The most common histopathological diagnosis reported is PMT mixed connective tissue, while the newer terminology 'PMT mixed epithelial and connective tissue type' has been described in 15 patients.

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.

Varied presentation of sinonasal phosphaturic mesenchymal tumour: report of a case series with follow-up

PURPOSE

Phosphaturic mesenchymal tumour (PMT) of the paranasal sinuses is a rare tumour that is associated with oncogenous osteomalacia causing predominant musculoskeletal symptoms. We present a series of eight patients diagnosed to have PMT of the paranasal sinuses with varied presentation and highlight the appropriate evaluation required to arrive at the diagnosis.

METHODS

Retrospective review of eight patients diagnosed to have PMT-causing tumour-induced osteomalacia with follow-up data.

RESULTS

Eight patients, 4 males and 4 females, aged 36-67 years (mean = 44 years) presented with vague musculoskeletal symptoms (6 patients) or epistaxis (3 patients). Six patients were found to have hypophosphatemia, phosphaturia and raised FGF-23 levels preoperatively. All eight patients were found to have a tumour in the nose and/ paranasal sinuses with one patient having intracranial extension. All patients were treated with endoscopic excision of these tumours which resulted in resolution of symptoms and normalisation of biochemical abnormalities. In addition, one patient required a craniofacial resection. Histopathological features were consistent with PMT mixed connective tissue variant. Two atypical patients were seen. The longest follow-up was for 5 years and there was no evidence of recurrence during the follow-up period in any patient.

CONCLUSION

Diagnosis of PMT of the paranasal sinuses causing oncogenous osteomalacia requires a high index of suspicion when there are no ENT symptoms. Appropriate biochemical tests and histopathology lead to the correct diagnosis. Total endoscopic surgical excision leads to a good outcome.

Tumor-induced hypophosphatemic osteomalacia caused by a mesenchymal tumor of the mandible managed by a segmental mandibulectomy and microvascular reconstruction with a free fibula flap

BACKGROUND

Tumor-induced osteomalacia is a rare paraneoplastic syndrome in which patients develop hypophosphatemia and osteomalacia.

METHODS AND RESULTS

Here, we report a unique case of a 42-year-old man who presented to our institution with a 1-year history of pain in his ribs, hips, lower back, and feet. Radiologic examination revealed a decrease in bone density and multiple insufficiency fractures. Laboratory evaluation revealed hypophosphatemia, low serum 1,25 dihydroxy vitamin D₃ , and elevated fibroblast growth factor 23 (FGF23). A positron emission tomography/CT scan showed increased uptake in the right mandibular third molar region. Panoramic radiography and CT scanning showed a lytic expansile bone lesion. A mandibular bone biopsy revealed a mixed connective tissue tumor. A right segmental mandibulectomy was performed, followed by microvascular reconstruction. The resection was confirmed by normalization of serum phosphate and FGF23.

CONCLUSION

Successful management of this condition was achieved, with complete surgical resection of the tumor and reconstructive surgery.

Phosphaturic mesenchymal tumor with an admixture of epithelial and mesenchymal elements in the jaws: clinicopathological and immunohistochemical analysis of 22 cases with literature review

Information on the heterogeneity of phosphaturic mesenchymal tumor, a rare entity associated with tumor-induced osteomalacia, is limited. In this retrospective analysis of 222 phosphaturic mesenchymal tumors, 22 cases exhibited mixed mesenchymal and epithelial elements, which we propose to term "phosphaturic mesenchymal tumor, mixed epithelial, and connective tissue type." Phosphaturic mesenchymal tumor of the mixed epithelial and connective tissue type showed a distinctive and significant male predominance (male:female = 2.67:1), with most patients diagnosed at <40 years old. Moreover, all tumors were mainly located in the alveolar bone with focal invasion into surrounding soft tissue and oral mucosa, which could be detected preoperatively by oral examination. The mesenchymal component, composed of spindled cells resembling fibroblasts or myofibroblasts arranged in a storiform or fascicular pattern, exhibited a less prominent vasculature and lower cellularity than the typical phosphaturic mesenchymal tumor (mixed connective tissue type). The epithelial component was typically haphazardly and diffusely distributed throughout the tumor, forming small, irregular nests resembling odontogenic epithelial nests. All cases were immunoreactive for fibroblast growth factor-23, somatostatin receptor 2A, and NSE in both components. Mostly also demonstrated positive staining for CD99 (21/22, 96%), CD56 (16/22, 73%), Bcl-2 (21/22, 96%), and D2-40 (19/22, 86%) in one or both components. S100 was positive in both components in one of seven cases. Interestingly, immunoreactivity was typically stronger and more diffuse in the epithelial than in the paired mesenchymal components. The mesenchymal component was also diffusely positive for CD68 (17/17, 100%) and showed variable focal staining for SMA (15/22, 68%) and CD34 (9/19, 47 %). These results indicate that phosphaturic mesenchymal tumor of the mixed epithelial and connective tissue type has distinctive clinicopathological characteristics and a polyimmunophenotypic profile.

Tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO), also known as oncogenic osteomalacia, is a rare paraneoplastic syndrome characterized by hypophosphatemia resulting from decreased tubular phosphate reabsorption, with a low or inappropriately normal level of active vitamin D. The culprit tumors of TIO could produce fibroblast growth factor 23 which plays a role in regulating renal Pi handling and 25-hydroxyvitamin D 1α-hydroxylase activity. Chronic hypophosphatemia could eventually lead to inadequate bone mineralization, presenting as osteomalacia. The diagnosis should be considered when patients manifest as hypophosphatemia and osteomalacia, or rickets and needs to be differentiated from other disorders of phosphate metabolism, such as the inhereditary diseases like X-linked hypophosphataemic rickets, autosomal dominant hypophosphataemic rickets, autosomal recessive hypophosphataemic rickets and acquired diseases like vitamin D deficiency. Localization of responsible tumors could be rather difficult since the vast majority are very small and could be everywhere in the body. A combination of thorough physical examination, laboratory tests and imaging techniques should be applied and sometimes a venous sampling may come into handy. The technology of somatostatin-receptor functional scintigraphy markedly facilitates the localization of TIO tumor. Patients undergoing complete removal of the causative neoplasm generally have favorable prognoses while a few have been reported to suffer from recurrence and metastasis. For those undetectable or unresectable cases, phosphate supplements and active vitamin D should be administrated and curative intended radiotherapy or ablation is optional.

Ethmoid tumor and oncogenic osteomalacia: Case report and review of the literature

INTRODUCTION

Oncogenic osteomalacia is a very rare disease usually caused by a phosphaturic mesenchymal tumor, particularly the "mixed connective tissue type", secreting FGF-23 hormone.

OBJECTIVE

The authors report a case of ethmoid tumor associated with oncogenic osteomalacia and discuss management based on a review of the literature.

CASE SUMMARY

A 41-year-old woman with multiple fractures causing major disability was diagnosed with early-onset osteoporosis. CT scan followed by MRI, performed due to the concomitant presence of nasal obstruction, showed a right ethmoid tumor in contact with the dura mater and periorbital tissues, but with no signs of invasion. Endoscopic resection was performed with reconstruction of the defect of the cribriform plate by a nasoseptal flap. Nasal and bone symptoms subsequently resolved. Histological examination revealed a phosphaturic mesenchymal tumor.

DISCUSSION

Twelve cases of mesenchymal tumor of the ethmoid sinus associated with oncogenic osteomalacia have been reported to date. FGF-23 assay and whole-body MRI with STIR sequence are useful for the diagnosis. A very favorable outcome is observed after surgical treatment in the majority of cases.

Glomus tumor as a cause of oncogenic osteomalacia

Many tumors that occasionally are benign in origin causes hypophosphatemic osteomalacia. Here we present a case of glomus tumor in a 59-year-old man with oncogenic osteomalacia. Diagnosis was made after observation of abnormal increase activity in octreotide scan. The magnetic resonance imaging showed a round lesion in left ankle joint. Surgical excision of tumor was curative and all symptoms and intractable hypophosphatemia improved after few weeks.

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.

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.

Phosphaturic Mesenchymal Tumor: 2 New Oral Cases and Review of 53 Cases in the Head and Neck

Phosphaturic mesenchymal tumor (PMT) is a rare neoplasm that secretes fibroblast growth factor-23 (FGF-23) and causes oncogenic osteomalacia. It occurs in adults with equal gender distribution and the most common location is the lower extremities, followed by the head and neck. Besides osteomalacia, the clinical presentation includes bone pain and multiple bone fractures. Microscopic features consist of spindle cells, multinucleated giant cells, and calcifications embedded in a chondromyxoid matrix. Laboratory findings indicate normal calcium and parathyroid levels, hypophosphatemia, and increased levels of FGF-23 that usually revert to normal after surgical removal. Due to its rarity, the purpose of the study was to report 2 new oral cases of PMT and to review the literature in the head and neck. The first case occurred in the gingiva and had been present for 6 years. The second case was a recurrence of a previously diagnosed PMT in the right mandible that metastasized to the lung and soft tissue. The literature review included 53 cases in the head and neck. There was a predilection for extra-oral sites (76%) compared to intra-oral sites (24%) with paranasal sinuses considered the most common location (38%) followed by the mandible (15%). There were 9 recurrences that included 3 malignant cases indicating a potentially aggressive tumor. Due to the indeterminate biological behavior of PMT and its rarity, a comprehensive evaluation of medical, laboratory, radiographic, and histological findings are crucial for a definitive diagnosis and treatment.

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

Tumour-induced osteomalacia (TIO) is a rare paraneoplastic syndrome characterised by severe hypophosphataemia and osteomalacia, with renal phosphate wasting that occurs in association with tumour. The epidemiology likewise aetiology is not known. The clinical presentation of TIO includes bone fractures, bone and muscular pains, and sometimes height and weight loss. TIO may be associated with mesenchymal tumours which may be benign or malignant in rare cases. Mesenchymal tumour itself may be related to fibroblast growth factor 23 (FGF23), which is responsible for hypophosphataemia and phosphaturia occurring in this paraneoplastic syndrome. Hypophosphataemia, phosphaturia and elevated alkaline phosphatase are the main laboratory readings that may lead to more precise investigations and better diagnosis. Finding the tumour can be a major diagnostic challenge and may involve total body magnetic resonance imaging, computed tomography and scintigraphy using radiolabelled somatostatin analogue. The treatment of choice for TIO is resection of a tumour with a wide margin to insure complete tumour removal, as recurrences of these tumours have been reported. We provide here an overview on the current available TIO case reports and review the best practices that may lead to earlier recognition of TIO and the subsequent treatment thereof, even though biochemical background and the long-term prognosis of the disease are not well understood. This review also includes a 4-year-long history of a patient that featured muscular pains, weakness and multiple stress fractures localised in the hips and vertebra with subsequent recovery after tumour resection. Because the occurrence of such a condition is rare, it may take years to correctly diagnose the disease, as is reported in this case report.

Electrolyte disorders associated with cancer

Patients with malignancies commonly experience abnormalities in serum electrolytes, including hyponatremia, hypokalemia, hyperkalemia, hypophosphatemia, and hypercalcemia. In many cases, the causes of these electolyte disturbances are due to common etiologies not unique to the underlying cancer. However, at other times, these electrolyte disorders signal the presence of paraneoplastic processes and portend a poor prognosis. Furthermore, the development of these electrolyte abnormalities may be associated with symptoms that can negatively affect quality of life and may prevent certain chemotherapeutic regimens. Thus, prompt recognition of these disorders and corrective therapy is critical in the care of the patient with cancer.

Bone scintigraphic patterns in patients of tumor induced osteomalacia

Tumor induced osteomalacia (TIO) or oncogenic osteomalacia is a rare condition associated with small tumor that secretes one of the phosphaturic hormones, i.e., fibroblast growth factor 23, resulting in abnormal phosphate metabolism. Patients may present with non-specific symptoms leading to delay in the diagnosis. Extensive skeletal involvement is frequently seen due to delay in the diagnosis and treatment. The small sized tumor and unexpected location make the identification of tumor difficult even after diagnosis of osteogenic osteomalacia. The bone scan done for the skeletal involvement may show the presence of metabolic features and the scan findings are a sensitive indicator of metabolic bone disorders. We present the bone scan findings in three patients diagnosed to have TIO.

Successful treatment of tumor-induced osteomalacia due to an intracranial tumor by fractionated stereotactic radiotherapy

CONTEXT

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome, characterized by tumor secretion of fibroblast growth factor-23 (FGF23) causing hypophosphatemia due to renal phosphate wasting. TIO is usually caused by small, benign, difficult-to-localize, mesenchymal tumors. Although surgery with wide excision of tumor borders is considered the "gold standard" for definitive therapy, it can be associated with considerable morbidity depending on the location. To date, radiation therapy has not been considered as an effective treatment modality in TIO.

OBJECTIVE

A 67-year-old female presented with multiple nontraumatic fractures, progressive bone pain, and muscle weakness for 4 years. She was found to have biochemical evidence of urinary phosphate wasting with low serum phosphorus, low-normal serum calcium, normal 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, and high serum FGF23 levels. TIO was diagnosed. Selective venous sampling for FGF23 confirmed that a 1.7-cm left frontal mass, radiographically similar to a meningioma, was the causative tumor. She declined surgery due to fear of complications and instead underwent fractionated stereotactic radiotherapy for 6 weeks.

RESULTS

In less than 4 years after radiation therapy, she was successfully weaned off phosphorus and calcitriol, starting from 2 g of oral phosphorus daily and 1 μg of calcitriol daily. Her symptoms have resolved, and she has not had any new fractures.

CONCLUSIONS

Stereotactic radiotherapy was an effective treatment modality for TIO in our patient. Fractionated stereotactic radiation therapy represents an alternative to surgery for patients with TIO who are not surgical candidates or who decline surgery.

Osteomalacia caused by skull base tumors: report of 2 cases

BACKGROUND AND IMPORTANCE

Tumor-induced osteomalacia (TIO) is an uncommon paraneoplastic syndrome rarely encountered in neurosurgical practice. We report on 2 cases of TIO caused by skull base tumors. Although the diagnosis of TIO is difficult to make and often is delayed because of the insidious nature of the symptoms, mostly systemic pain and weakness, it is curable once it is diagnosed and properly treated.

CLINICAL PRESENTATION

Both patients presented with severe pain developing in the lower extremities and moving out to the entire body, as well as difficulty moving. They were diagnosed with TIO several years after onset. A high level of serum FGF23 was confirmed, and whole-body imaging studies demonstrated tumors in the middle and anterior cranial base, respectively. The patient with the anterior cranial base tumor had a history of hemorrhage into the frontal lobe and partial resection. En bloc resection of tumor with surrounding skull bone was performed. The histological diagnosis for both cases was phosphaturic mesenchymal tumor, mixed connective tissue variant.

CONCLUSION

The level of FGF23 normalized immediately after surgery. Both patients experienced a dramatic relief of pain and recovery of muscle power. Although reports of osteomalacia caused by tumors in the neurosurgical field are extremely rare in the literature, its true incidence is unknown. We emphasize the importance of recognition of this syndrome and recommend total resection of tumors when possible.

FGF23 and Phosphate Wasting Disorders

A decade ago, only two hormones, parathyroid hormone and 1,25(OH)2D, were widely recognized to directly affect phosphate homeostasis. Since the discovery of fibroblast growth factor 23 (FGF23) in 2000 (1), our understanding of the mechanisms of phosphate homeostasis and of bone mineralization has grown exponentially. FGF23 is the link between intestine, bone, and kidney together in phosphate regulation. However, we still do not know the complex mechanism of phosphate homeostasis and bone mineralization. The physiological role of FGF23 is to regulate serum phosphate. Secreted mainly by osteocytes and osteoblasts in the skeleton (2,3), it modulates kidney handling of phosphate reabsorption and calcitriol production. Genetic and acquired abnormalities in FGF23 structure and metabolism cause conditions of either hyper-FGF23 or hypo-FGF23. Hyper-FGF23 is related to hypophosphatemia, while hypo-FGF23 is related to hyperphosphatemia. Both hyper-FGF23 and hypo-FGF23 are detrimental to humans. In this review, we will discuss the pathophysiology of FGF23 and hyper-FGF23 related renal phosphate wasting disorders (4).

Anesthesia for oncogenic osteomalacia--a rare paraneoplastic syndrome

Two patients with a diagnosis of oncogenic osteomalacia are described. This rare disease, characterized by secretion of fibroblast growth factor-23 by the tumor cells, causes myopathy, extreme debilitation and severe osteopathy because of severe hypophosphatemia. Both patients presented with severe bone pain, pathological fractures and proximal muscle weakness. Multiple diagnostic tools had to be utilized to settle the diagnosis of this rare disease. Although supplemental therapy for hypophosphatemia is usually started preoperatively, surgical excision of the causative tumor is the only definite treatment. Surgery is almost always curative; however, there is a lack of discourse in the literature regarding the anesthetic implications for the disease. The complete pathophysiology of the disease, clinical picture, its diagnostic intricacies as well as the salient points in its anesthetic management are discussed in this report.

[Oncogenic osteomalacia: increased production of fibroblast growth factor 23 is not the unique actor]

The importance of fibroblast growth factor 23 (FGF 23) has been highlighted in the mechanism of urinary leakage of phosphate in the oncogenic osteomalacia (OO). It is now a component of diagnosis of this disease. We report a 58-year-old man who presented with osteomalacia and hypophosphatemia secondary to urinary leakage of phosphorus. Although serum FGF 23 was normal, the diagnosis of OO was obtained after another cause of acquired prolonged hypophosphatemia has been excluded (hyperparathyroidism and Fanconi syndrome in particular). The search for a deep tumor was performed, allowing the detection of a 12 mm hemangiopericytoma in the upper thigh. Its removal allowed the rapid resolution of clinical symptoms and laboratory abnormalities. The importance of functional sequelae in OO depends on prompt diagnosis. Tumorectomy remains the optimal treatment. Thus, the search for a secreting tumor is essential even in the absence of elevated serum FGF 23.

Tumor-induced osteomalacia: a single center experience

OBJECTIVE

To describe the clinical presentation, localization modalities, and management of patients with tumor-induced osteomalacia (TIO).

METHODS

We performed a retrospective analysis of case records of patients diagnosed with TIO between January 1996 and March 2010 at our institution in Mumbai, India.

RESULTS

Nine patients (6 female and 3 male) with a mean age of 37.5 ± 17.5 years with biochemical and imaging evidence of TIO were included in the study. Overall, patients presented with proximal muscle weakness and pain. Three patients had neurofibromatosis 1, one had isolated schwannoma, and one had epidermal nevus syndrome. The mean delay in diagnosis was 7.67 years. Biochemical studies revealed normal serum calcium (mean, 9.2 ± 0.8 mg/dL), low serum phosphorus (mean, 1.36 ± 0.54 mg/dL), and low maximal tubular reabsorption of phosphorus factored for glomerular filtration rate (mean, 0.94 ± 0.49 mg/dL). Fibroblast growth factor-23 was increased in 3 of the patients without neurofibromatosis but was normal or near-normal in all the patients with neurofibromas. A fludeoxyglucose F 18 positron emission tomography (FDG PET) scan helped to localize the tumors in 4 of the 5 patients with diagnoses other than neurofibromatosis. Three patients underwent surgical excision and were cured. One patient underwent biopsy and partial excision. Histopathologic findings were suggestive of phosphaturic mesenchymal tumor, benign fibrous histiocytoma, nonossifying fibroma, and sciatic nerve schwannoma.

CONCLUSION

There is a well-known delay in the diagnosis of TIO. FDG PET is a useful modality for localization of tumors. Preoperative localization increases the odds for cure after surgical excision.

Tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO) is a rare and fascinating paraneoplastic syndrome in which patients present with bone pain, fractures, and muscle weakness. The cause is high blood levels of the recently identified phosphate and vitamin D-regulating hormone, fibroblast growth factor 23 (FGF23). In TIO, FGF23 is secreted by mesenchymal tumors that are usually benign, but are typically very small and difficult to locate. FGF23 acts primarily at the renal tubule and impairs phosphate reabsorption and 1α-hydroxylation of 25-hydroxyvitamin D, leading to hypophosphatemia and low levels of 1,25-dihydroxy vitamin D. A step-wise approach utilizing functional imaging (F-18 fluorodeoxyglucose positron emission tomography and octreotide scintigraphy) followed by anatomical imaging (computed tomography and/or magnetic resonance imaging), and, if needed, selective venous sampling with measurement of FGF23 is usually successful in locating the tumors. For tumors that cannot be located, medical treatment with phosphate supplements and active vitamin D (calcitriol or alphacalcidiol) is usually successful; however, the medical regimen can be cumbersome and associated with complications. This review summarizes the current understanding of the pathophysiology of the disease and provides guidance in evaluating and treating these patients. Novel imaging modalities and medical treatments, which hold promise for the future, are also reviewed.

Oncogenic osteomalacia from nasal cavity giant cell tumor

BACKGROUND

Oncogenic osteomalacia is a rare paraneoplastic syndrome characterized by osteomalacia, which occurs as a result of excess renal phosphate excretion caused by fibroblast growth factor-23 secreted by mesenchymal tumors. This entity is rare in head and neck cancers. We report a rare case of oncogenic osteomalacia in a patient with an anterior skull base giant cell tumor.

METHODS AND RESULTS

A 34-year-old woman presented with a 5-year history of progressive weakness in both lower limbs and the trunk. Hypophosphatemia and hypocalcemia had been noted by a local physician, but her symptoms persisted despite receiving calcium and vitamin D supplements. A recent onset of epistaxis and nasal blockage led to referral to the head and neck services. Nasal endoscopy revealed a left nasal cavity mass. Further evaluation with imaging studies revealed a mass in the nasal cavity with intracranial extension. Biopsy of the lesion suggested a neurogenic tumor. A putative diagnosis of anterior skull base neurogenic tumor with paraneoplastic hypophosphatemia was made. After the biochemical parameters were corrected, the patient underwent craniofacial resection. The final histopathologic study suggested the lesion as a "giant cell tumor." During the postoperative period the patient's biochemical and clinical symptoms improved dramatically, allowing her to regain normal mobility.

CONCLUSIONS

Clinicians and pathologists must be aware of the clinical symptoms, laboratory abnormalities, and pathologic features of oncogenic osteomalacia, which may be caused by tumors in the head and neck and thus make an exhaustive effort to diagnose the same.

Oncogenic osteomalacia in a patient with an ethmoid sinus tumour

OBJECTIVE

To highlight the clinical presentation and management of a rare case of oncogenic osteomalacia due to an ethmoid sinus tumour.

MATERIALS AND METHODS

We examined the case records of a 55-year-old man who presented with progressive fatigue, weakness and bone pain, and noted the clinical presentation, laboratory investigations, computed tomography findings, operative notes and follow-up details.

CONCLUSION

Oncogenic osteomalacia secondary to a paranasal sinus neoplasm is a rare entity. The causative tumour is often occult and may be missed by routine clinical examination. This case report illustrates the appropriate pattern of evaluation and management to ensure a successful outcome.

Oncogenic osteomalacia caused by a phosphaturic mesenchymal tumor of the thoracic spine

Phosphaturic mesenchymal tumors that cause the paraneoplastic syndrome known as oncogenic osteomalacia are rare. The authors report on the case of a 57-year-old man with a history of osteomalacia and in whom was diagnosed a thoracic spine tumor at the T-4 level. Complete tumor resection was accomplished. The histological diagnosis was phosphaturic mesenchymal tumor (mixed connective tissue variant). After lesion removal, the paraneoplastic syndrome resolved. At the 24-month follow-up, no recurrence of the disease was observed. The clinical presentation, surgical technique, and follow-up in this case were reviewed in detail.

Tumor-induced osteomalacia: successful treatment by radio-guided tumor surgery

Tumor-induced osteomalacia is a rare syndrome characterized by urinary phosphate loss with hypophosphatemic osteomalacia. The proposed pathogenetic mechanism is paraneoplastic secretion of phosphaturic factors (so-called phosphatonins).We describe a 34-year-old male patient who presented with severe pain of the spine and ribs for at least 2 years. Bone scintigraphy using Technetium hydroxymethylene diphosphonate (Tc HDP) showed multiple lesions suggesting metastatic disease. Bone biopsy however revealed osteomalacia. The patient had subnormal plasma phosphate levels (0.42 mmol/L; normal range, 0.87-1.45) and markedly increased phosphate clearance (82.8 mL/min; normal range, 5.4-16.2). The patient was treated with phosphate supplementation (up to 5 g daily) along with calcium (1000 mg daily) and calcitriol (1.5 microg daily). Although this therapy did not correct hypophosphatemia, it resulted in complete relief of pain within several months. (111)In pentetreotide scintigraphy showed a tiny lesion of 1-cm diameter, which could be localized to the left femoral neck in close vicinity to the greater trochanter by MRI and image fusion analysis. This lesion had not been visualized by Tc-99m HDP bone scintigraphy. Intraoperatively, use of a hand-held gamma probe after administration of (111)Indium pentetreotide ((111)In pentetreotide) clearly identified the tumor, which was completely removed and was shown to be a hemangiopericytoma. After removal of the tumor, phosphate metabolism normalized within 1 week without requirement of phosphate supplementation. Hypophosphatemic osteomalacia, although rare, raises an important differential diagnosis. An underlying tumor may be detected only by (111)In pentetreotide scintigraphy. Preoperative labeling with (111)In pentetreotide is a useful tool in detecting these tumors during surgery.This 34 year old man with osteomalacia had a small causative hemangiopericytoma detected in the indium pentetreotide scintography.

Case report: Solitary plasmacytoma of bone with oncogenic osteomalacia: recurrence of tumour confirmed by PET/CT. A case report with a review of the radiological literature

We describe a case of oncogenic osteomalacia secondary to solitary plasmacytoma of the vertebral body of T3. The patient presented with symptoms of hypophosphataemia. Following the initial diagnosis, the lesion was surgically resected with good results, although several follow-up procedures, including bone grafting, were necessary to stabilize the thoracic spine. The lesion recurred almost 15 years after its initial resection, again presenting with hypophosphataemia and neurological symptoms suggestive of local tumour recurrence. A variety of radiological examinations were performed in an attempt to confirm and localize recurrent tumour, including bone scintigraphy, (111)indium octreotide scintigraphy, high-resolution CT and MRI of the thoracic spine, but these yielded only negative or equivocal results owing, in part, to the presence of extensive post-operative changes, and also to a difference in the MR signals of the recurrent and original tumours. Positron emission tomography (PET/CT) demonstrated a solitary focus of intense fluorodeoxyglucose uptake in the T3 vertebral body, enabling a definitive diagnosis of recurrent plasmacytoma. This case illustrates the diagnostic value of PET/CT in the setting of challenging post-operative changes in the surrounding tissue and in the appearance of the tumour itself. Relevant related imaging literature is also reviewed.

Sporadic adult-onset hypophosphatemic osteomalacia caused by excessive action of fibroblast growth factor 23

A 50-year-old man without family history of metabolic bone disease was referred to our hospital with a 5-year history of progressively worsening spinal and bilateral diffuse leg pain and proximal muscle weakness. Two years before admission, he was diagnosed as ankylosing spondylitis by a rheumatologist and was maintained on low-dose prednisone therapy without benefit. He developed progressive spinal and thoracic deformities, resulting in a 10 cm loss in height in the preceding 2 years. On physical examination, marked thoracic kyphosis and pectus carinatum was noted. Plain radiograph revealed pseudofracture in the right femoral neck. Laboratory findings showed a normal level of serum calcium, elevated level of serum alkaline phosphatase and inappropriately increased urinary phosphate excretion despite extreme hypophosphatemia. He was diagnosed as adult-onset hypophosphatemic osteomalacia caused by renal phosphate wasting. Serum fibroblast growth factor 23 was the upper limit of normal despite extreme hypophosphatemia and no neoplastic lesion potentially inducing hypophosphatemic osteomalacia could be identified in a thorough search including imaging studies of his entire body. Oral administration of phosphate and activated vitamin D together with dipyridamole relieved the persistent pain and weakness, and he became fully ambulatory.

Imaging in the investigation of paraneoplastic syndromes

Paraneoplastic syndromes are a heterogeneous group of disease presentations caused by underlying tumours. As they are non-metastatic in nature an intensive diagnostic evaluation is warranted to identify potentially curable lesions. The selection of the appropriate method of imaging is important in these cases, especially when history and physical examination are unrevealing. In this review the important paraneoplastic syndromes and underlying malignancies are discussed along with relevant imaging strategies.

A paranasal tumor associated with tumor-induced osteomalacia

BACKGROUND

Tumor-induced osteomalacia (TIO) is an extremely rare paraneoplastic syndrome associated with mesenchymal tumors in the craniofacial region.

METHODS

We treated a 24-year-old Japanese woman with paranasal sinus tumor and a low serum phosphate level who presented with nasal obstruction and systemic bone fractures. Serum fibroblast growth factor 23 (FGF-23) was measured before and after surgery.

RESULTS

After surgery, her symptoms were resolved and the serum phosphate and FGF-23 levels became normalized.

CONCLUSION

FGF-23 is thought to be a useful diagnostic marker in patients with craniofacial tumors associated with multiple systemic fractures.

[Hyperparathyroidism associated with hypophosphatemic osteomalacia: case report and review of the literature]

Adult-onset hypophosphatemic osteomalacia is a rare disease characterized by hypophosphatemia, increased levels of alkaline phosphatase and decreased bone mass. Oral supplementation with phosphate and vitamin D is the main treatment and, in cases of oncogenic osteomalacia, tumor resection is mandatory. We report the case of a patient with hypophosphatemic osteomalacia of an unknown cause. Despite extensive search, no tumor was found. The patient was treated with phosphate for a long period and developed tertiary hyperparathyroidism. Serum PTH levels did not return to normal after surgical excision of three parathyroids and the patient refused to continue clinical investigation and treatment. After ten years absent from the hospital, during which medications were used irregularly, she was admitted with multiple fractures and respiratory insufficiency caused by severe thoracic deformities, and died. The authors discuss the relationship between osteomalacia and hyperparathyroidism and the aggressive course of the disease.

The development of hypophosphataemic osteomalacia with myopathy in two patients with HIV infection receiving tenofovir therapy

We report two cases in which osteomalacia developed in patients on tenofovir-containing highly active antiretroviral therapy (HAART) in the context of Fanconi syndrome with hypophosphataemia. Bone pain was the presenting feature and myopathy followed in one case. Disability was reversed with withdrawal of the drug and with mineral supplementation. The cases highlight the importance of considering the diagnosis of osteomalacia in patients treated with tenofovir. A possible association with incipient acute renal failure, particularly during nonsteroidal anti-inflammatory drug (NSAID) use, needs further investigation.

Acquired hypophosphatemic osteomalacia associated with multiple myeloma

Hypophosphatemic osteomalacia is a rare but important complication of multiple myeloma. In these cases, the pathophysiology of the phosphate renal wasting notably differs from oncogenic osteomalacia and is due to light-chain nephropathy, resulting in proximal tubular dysfunction which is not restricted to phosphate handling. These patients seems to have a distinct type of plasma cell disorder characterized by a slow progression of the tumor and by an early phase dominated by the metabolic complications of the renal proximal tubular dysfunction. For this reason hypophosphatemic osteomalacia is the presenting feature that leads to the diagnosis of multiple myeloma in most of these patients. Recognition of this complication is important, since supportive treatment with phosphate supplements and calcitriol may substantially alleviate pain and weakness associated with hypophosphatemia.

Hypophosphaturic mesenchymal tumor of the ethmoid associated with oncogenic osteomalacia

Oncogenic osteomalacia is an uncommon syndrome characterized by bone pain, proximal muscle weakness, hypophosphatemia, hyperphosphaturia, and a low plasma concentration of 1,25-dihydroxy-vitamin D. The disease affects both sexes at around 40 years of age, although it can sometimes affect children and adolescents. Generally, the syndrome is associated with a tumor, usually benign, of mesenchymal origin and is resolved after removal of the tumor; this syndrome can sometimes be associated with malignant tumors. These tumors seem to be histologically heterogeneous and are generally localized in soft tissues and bone. In this article, a case of oncogenic osteomalacia associated with a hypophosphaturic mesenchymal tumor of the ethmoid is reported in a 24-year-old man. After surgical and radical removal of the tumor, the patient noted a decrease in the clinical symptoms and signs.