Phosphaturic mesenchymal tumor-induced rickets

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.

Alkaline phosphatase in clinical practice in childhood: Focus on rickets

Serum alkaline phosphatase (ALP) and its isoenzymes reflect bone metabolism: ALP increases the ratio of inorganic phosphate to pyrophosphate systemically and facilitates mineralization as well as reduces extracellular pyrophosphate concentration, an inhibitor of mineral formation. On the contrary, low ALP activity is associated with reduction of bone turnover. ALP includes four isoenzymes depending on the site of tissue expression: intestinal ALP, placental ALP, germ cell ALP and tissue nonspecific ALP or liver/bone/kidney ALP. The bone isoenzyme (B-ALP) is involved in bone calcification and is a marker of bone turnover as a result of osteoblastic activity. ALP and its isoenzymes are crucial in the diagnostic process of all the forms of rickets.The most common cause of rickets is vitamin D nutritional deficiency. The aim of this review is to update on the role played by ALP serum concentrations as a relevant marker in thediagnosis and treatment of rickets. Indeed, the diagnosis of rickets is based on its clinical, radiological and laboratory characteristics. An elevated ALP level is one of the markers for the diagnosis of rickets in children, though it is also associated with bone formation process. ALP is also useful for the differentiation between rickets and other disorders that can mimic rickets because of their clinical and laboratory characteristics, and, together with other biochemical markers, is crucial for the differential diagnosis of the different forms of rickets. Age, severity and duration of rickets may also modulate ALP elevation. Finally, ALP measurements are useful in clinical and therapeutic follow-up.

Diagnostic Utility of Somatostatin Receptor 2A Immunohistochemistry for Tumor-induced Osteomalacia

CONTEXT

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic disorder caused by excessive fibroblast growth factor 23 (FGF23) secretion. FGF23 immunohistochemistry (IHC) is proposed as a useful adjunctive marker to confirm TIO diagnosis. However, it often stains focally, limiting its diagnostic utility.

OBJECTIVE

This work aimed to compare the diagnostic performance between somatostatin receptor 2A (SSTR2A) and FGF23 IHC for TIO.

METHODS

We retrospectively reviewed TIO-diagnosed patients in Severance Hospital between July 2006 and May 2020. Histologic evaluation was performed using histoscore (H score) (expression area proportion score [0-2] × intensity score [1-3], [total, 0-6]). FGF23 and SSTR2A IHC were performed using unstained slides from 18 localized TIO patients and 9 and 15 non-TIO controls with bone and soft-tissue tumors, respectively. SSTR2A positivity was defined as cytoplasmic, membranous, or Golgi staining in more than 1% of tumor cells, and negativity as nonspecific nuclear staining. FGF23 positivity was defined as cytoplasmic expression in more than 1% of the tumor area and negativity as nonspecific nuclear staining.

RESULTS

Suspicious lesions were successfully detected in 14 of 15 patients who underwent 68Ga-DOTATOC scans. Diffuse cytoplasmic SSTR2A expression was identified in all TIO patients and focal weak nuclear staining in 12 of 15 controls. FGF23 cytoplasmic expression was identified in 11 of 18 TIO patients and diffuse nuclear staining in 9 of 9 controls. The H score was higher in SSTR2A than in FGF23 IHC (median [interquartile range]: 6 [6-6] vs 1 [0-2], P < .001).

CONCLUSION

SSTR2A IHC with H-score quantification might be a more sensitive, adjunctive diagnostic tool than FGF23 IHC for TIO diagnosis.

FGF-23 transmitted tumor - induced hypophosphatemic osteomalacia: a rare case of a young woman with recurrent fractures and review of the literature

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Tumor-transmitted osteomalacia is a rare FGF 23 transmitted phosphaturic disease.

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Delay of diagnosis is common due to small and clinically silent underlying tumors.

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The most sensitive imaging modality is ⁶⁸Ga-DOTA-TOC-PET/CT-scan.

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Complete resection of the tumor mass cures this paraneoplastic disease.

We present a case of tumor-induced osteomalacia (TIO) in a young woman of 22 years. The fibroblast growth factor 23 transmitting tumor in her left foot remained undetected for several years. She suffered several fractures including insufficiency fractures of both femoral necks requiring bilateral proximal femoral nailing. After phosphaturia was diagnosed any known genetic etiology was excluded. Even advanced imaging modalities were unable to detect the clinically silent tumor until an ⁶⁸Ga-DOTA-TOC-PET/CT-scan revealed a mass with paraneoplastic activity in the left foot. Complete resection of the tumor proved to cure her condition after 9 years of uncertainty and suffering. Serum phosphate levels returned to normal within days.

After presentation of the case report, the current literature on published cases of TIO between 1956 and 2021 is summarized to emphasize the importance of an accurate and early diagnosis. Our case report aims to illustrate that a long latency period of diagnosis may be avoided utilizing the latest imaging techniques to spare affected patients from long treatment of symptoms instead of finding the underlying cause.

Ameloblastic Fibroodontoma of Mandible Causing Tumor Induced Osteomalacia: A Case Report with Review of 88 Phosphaturic Oral Neoplasms

Tumor induced osteomalacia (TIO) is a rare paraneoplastic syndrome associated with tumors secreting fibroblast growth factor 23, which induces osteomalacia. Microscopically, these tumors most commonly show benign phosphaturic mesenchymal tumors. We report the first case of phosphaturic ameloblastic fibro-odontoma (AFO) manifesting as osteomalacia. Our index patient was a 33-year-old male who was diagnosed with TIO and AFO in the mandible was identified as the cause. Our case is unique as AFO is considered as a hamartoma. To the best of our knowledge, there is no hamartoma reported till date causing phosphaturic osteomalacia. As AFO demonstrates mixed epithelial and mesenchymal origin, we propose a new histopathological subtype of TIO-"phosphaturic tumor of mixed epithelial and mesenchymal origin". A review of literature focused on TIO caused by oral lesions revealed 88 oral neoplasms which matched our search criteria. Due to the rarity and unpredictable behavior of TIOs, a high index of suspicion, a broad diagnostic approach, detailed history and multidisciplinary investigations are crucial for establishing the definitive diagnosis and proper treatment recommendations.

Occult tumour-induced osteomalacia causing lesion detected by FDG-PET/CT scan

Oncogenic osteomalacia is a rare condition, with overproduction of fibroblast growth factor 23, leading to hypophosphatemia, phosphaturia. If it is associated with benign mesenchymal tumor, then resection of tumor is curable. Thus, detection and localization of the lesion are of utmost importance. We report a case, where ¹⁸F-FDG PET/CT scan was useful in detection of such occult lesion.

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.

Phosphaturic Mesenchymal Tumor of Soft Tissue of the Foot: Report of a Case With Review of the Literature

Phosphaturic mesenchymal tumor (PMT) is a rare neoplasm that ectopically secretes fibroblast growth factor 23, a bone cell-derived protein that regulates phosphate homeostasis. The overproduction of fibroblast growth factor 23 causes a paraneoplastic syndrome characterized by hyperphosphaturia, hypophosphatemia, hypovitaminosis D, and vitamin D refractory rickets/osteomalacia, effects that disappear with tumor removal. The PMT may occur in several anatomic regions, mainly in the limbs, usually involving both soft tissue and bone. Acral locations occur in 10% to 15% of the cases, mostly in the feet, with 95 cases reported in this anatomic region to date. We report a case of a PMT in a young adult male who presented in 2007 with the classic constellation of signs and symptoms. A small soft-tissue tumor was detected in his right heel, 3 years after exhaustively seeking for it by various imaging techniques performed at different institutions. Before the tumor was detected, attempts to manage this patient's osteomalacia with phosphate and vitamin D (both calcitriol and ergocalciferol) supplementation were unsuccessful. Following surgical resection, the patient experienced prompt correction of the phosphaturia and gradual reconstitution of his bone mineralization. The pathologic diagnosis was (benign) PMT, mixed connective tissue type. In 2019, 12 years after resection, the patient is asymptomatic, and his bone mineral homeostasis has been restored.

Review of paraneoplastic syndromes in children

Paraneoplastic syndromes are defined as clinical syndromes that are not related to direct tumor invasion or compression but are secondary to tumor secretion of functional peptides/hormones or related to immune cross-reactivity with normal host tissue. Paraneoplastic syndromes have a wide range of presentations and can present before the primary malignancy or tumor recurrence is diagnosed. They can mimic non-neoplastic processes, making detection, diagnosis and treatment difficult. However, they can also provide clues to the presence of an underlying malignancy. In this paper, we reviewed a range of paraneoplastic syndromes that can occur in children including: (1) neurologic (opsoclonus-myoclonus, limbic, anti-N-methyl-d-aspartate [NMDA] and anti-Ma2 encephalitis and myasthenia gravis); (2) endocrine (neuroendocrine tumors, hypercalcemia, SIADH [syndrome of inappropriate antidiuretic hormone secretion], osteomalacia/rickets and ROHHAD [rapid onset of obesity, hypoventilation, hypothalamic dysfunction and autonomic dysregulation]); and (3) dermatologic/rheumatologic syndromes (hypertrophic osteoarthropathy and paraneoplastic pemphigus). Familiarity with these syndromes can aid in early diagnosis, treatment and imaging optimization.

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.

Phosphaturic mesenchymal tumor and related wound problem

INTRODUCTION

Phosphaturic mesenchymal tumor mixed connective tissue type (PMT/MCT) is the most common type (up to 90%) of phosphaturic mesenchymal tumor (PMT), a rare clinicopathologic entity. Besides overproduction of fibroblast growth factor 23 (FGF23), there is a big variation of immunohistochemical characteristic across types of PMT, which makes it difficult to obtain an early diagnosis of PMT/MCT. As a benign tumor, PMT/MCT usually happens in subcutaneous tissues and leads to nonhealing of wound. A complete excision of PMT/MCT facilitates wound healing.

CONCLUSIONS

Review of the existing evidence indicates that early diagnosis of PMT/MCT is critically important when treating PMT/MCT wound. Hence standardization of early diagnosis for PMT/MCT is mandated.

X-Linked Hypophosphatemia and FGF23-Related Hypophosphatemic Diseases: Prospect for New Treatment

Phosphate plays essential roles in many biological processes, and the serum phosphate level is tightly controlled. Chronic hypophosphatemia causes impaired mineralization of the bone matrix and results in rickets and osteomalacia. Fibroblast growth factor 23 (FGF23) is a bone-derived hormone that regulates phosphate metabolism. FGF23 excess induces hypophosphatemia via impaired phosphate reabsorption in the renal proximal tubules and decreased phosphate absorption in the intestines. There are several types of genetic and acquired FGF23-related hypophosphatemic diseases. Among these diseases, X-linked hypophosphatemia (XLH), which is caused by inactivating mutations in the phosphate-regulating endopeptidase homolog, X-linked (PHEX) gene, is the most prevalent form of genetic FGF23-related hypophosphatemic rickets. Another clinically relevant form of FGF23-related hypophosphatemic disease is tumor-induced osteomalacia (TIO), a paraneoplastic syndrome associated with FGF23-producing tumors. A combination of active vitamin D and phosphate salts is the current medical therapy used to treat patients with XLH and inoperative TIO. However, this therapy has certain efficacy- and safety-associated limitations. Several measures to inhibit FGF23 activity have been considered as possible new treatments for FGF23-related hypophosphatemic diseases. In particular, a humanized monoclonal antibody for FGF23 (burosumab) is a promising treatment in patients with XLH and TIO. This review will focus on the phosphate metabolism and the pathogenesis and treatment of FGF23-related hypophosphatemic diseases.

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.

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.

Sinonasal Phosphaturic Mesenchymal Tumor: A Rare and Misinterpreted Entity

Objectives Oncogenic osteomalacia is a paraneoplastic syndrome in which the tumor secretes a peptide-like hormone, fibroblast growth factor, resulting in urinary loss of phosphates. Methods We present the case of a 50-year-old woman with a benign phosphaturic mesenchymal tumor (PMT) involving the ethmoid sinus with obstruction of the ostiomeatal complex causing unilateral nasal airway obstruction. Results The tumor was initially thought to be an esthesioneuroblastoma based on primary pathology interpretation and on clinical and radiographic appearance. However, a benign PMT was later confirmed by further testing. Conclusion The tumor was removed entirely by the endoscopic transnasal approach, leading to a full resolution of symptoms.

Tumor-induced rickets in a child with a central giant cell granuloma: a case report

Tumor-induced osteomalacia/rickets is a rare paraneoplastic disorder associated with a tumor-producing fibroblast growth factor 23 (FGF23). We present a child with symptoms of rickets as the first clinical sign of a central giant cell granuloma (CGCG) with high serum levels of FGF23, a hormone associated with decreased phosphate resorption. A 3-year-old boy presented with a limp and 6 months later with painless growth of the jaw. On examination gingival hypertrophy and genu varum were observed. Investigations revealed hypophosphatemia, normal 1,25 and 25 (OH) vitamin D, and high alkaline phosphatase. An MRI showed an osteolytic lesion of the maxilla. Radiographs revealed typical rachitic findings. Incisional biopsy of the tumor revealed a CGCG with mesenchymal matrix. The CGCG was initially treated with calcitonin, but the lesions continued to grow, making it necessary to perform tracheostomy and gastrostomy. One year after onset the hyperphosphaturia worsened, necessitating increasing oral phosphate supplements up to 100 mg/kg per day of elemental phosphorus. FGF23 levels were extremely high. Total removal of the tumor was impossible, and partial reduction was achieved after percutaneous computed tomography-guided radiofrequency, local instillation of triamcinolone, and oral propranolol. Compassionate use of cinacalcet was unsuccessful in preventing phosphaturia. The tumor slowly regressed after the third year of disease; phosphaturia improved, allowing the tapering of phosphate supplements, and FGF23 levels normalized. Tumor-induced osteomalacia/rickets is uncommon in children and is challenging for physicians to diagnose. It should be suspected in patients with intractable osteomalacia or rickets. A tumor should be ruled out if FGF23 levels are high.

Sinonasal phosphaturic mesenchymal tumor: Case report and systematic review

We report a case of sinonasal phosphaturic mesenchymal tumor (PMT) and conduct a systematic review of the literature to highlight a unique paraneoplastic syndrome associated with PMT. We used English language publications from Medline and Cochrane databases (1970-2013) as data sources. A systematic review of the literature was conducted. All reported cases of head and neck PMTs were included. The presence or absence of the associated paraneoplastic syndrome was noted. We found 33 cases of PMT in the head and neck reported in the literature, 17 of which occurred in the sinonasal area. Approximately 5% of all PMTs are located in the head and neck. Just greater than half are concentrated in the sinonasal area, and the remaining involve various bony and soft tissue structures of the head and neck. PMT is sometimes associated with a paraneoplastic syndrome of tumor-induced (oncogenic) osteomalacia (TIO) causing bone pain, muscle weakness, and pathologic fractures. We present the 18th reported case of sinonasal PMT. A smooth mucosa-covered midline intraseptal mass filling the posterior nasal cavity with destruction and erosion of the skull base was found in an adult male. The patient underwent successful endoscopic resection with wide negative margins and is without recurrence at 24-month follow-up. PMT is a benign, locally aggressive tumor with rare malignant transformation. Knowledge of the bony invasion and destruction caused by this tumor is essential in planning surgical resection with wide negative margins. Familiarity with the associated TIO is essential to investigate for and manage any associated bony morbidity.

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.

Recurrent phosphaturic mesenchymal tumour of the temporal bone causing deafness and facial nerve palsy

OBJECTIVE

We describe the first reported case of a phosphaturic mesenchymal tumour, mixed connective tissue variant, invading the temporal bone.

CASE REPORT

A female patient presented with increasing deafness. On examination there appeared to be a mass behind an intact tympanic membrane. Further radiological investigation showed a vascular mass occupying the middle ear, mastoid and internal auditory meatus. This was surgically resected and revealed to be a benign phosphaturic mesenchymal tumour, mixed connective tissue variant. The tumour recurred a year later, presenting as facial nerve palsy. A revision procedure was carried out; the tumour was excised with the sacrifice of a segment of the facial nerve, and a facial-hypoglossal nerve anastomosis was performed.

CONCLUSION

This case report highlights the occurrence of this benign but sometimes aggressive tumour, of which both clinicians and pathologists should be aware. Early recognition of the condition remains of utmost importance to minimise the debilitating consequences of long-term osteomalacia in affected patients, and to prevent extracranial and intracranial complications caused by the tumour.

Evaluation of hypophosphatemia: lessons from patients with genetic disorders

Phosphate is a key component of several physiologic pathways, such as skeletal development, bone mineralization, membrane composition, nucleotide structure, maintenance of plasma pH, and cellular signaling. The kidneys have a key role in phosphate homeostasis, with 3 hormones having important roles in renal phosphate handling: parathyroid hormone, fibroblast growth factor 23 (FGF-23), and 1,25-dihydroxyvitamin D. Independent of the genetic diseases affecting the FGF-23 pathway (such as hypophosphatemic rickets), hypophosphatemia is a frequent condition encountered in daily practice, and untreated critical hypophosphatemia can induce hemolysis, rhabdomyolysis, respiratory failure, cardiac dysfunction, and neurologic impairment. Rapid correction thus is necessary to avoid severe complications. The aims of this teaching case are to summarize the causes and biological evaluation of hypophosphatemia and provide an overview of our current understanding of phosphate metabolism.

Using (18)F-FDG PET/CT to Detect an Occult Mesenchymal Tumor Causing Oncogenic Osteomalacia

Oncogenic osteomalacia is a rare paraneoplastic syndrome characterized by renal phosphate excretion, hypophosphatemia, and osteomalacia. This syndrome is often caused by tumors of mesenchymal origin. Patients with oncogenic osteomalacia have abnormal bone mineralization, resulting in a high frequency of fractures. Tumor resection is the treatment of choice, as it will often correct the metabolic imbalance. Although oncogenic osteomalacia is a potentially curable disease, diagnosis is difficult and often delayed because of the small size and sporadic location of the tumor. Bone scintigraphy and radiography best characterize osteomalacia; magnetic resonance imaging findings are nonspecific. Here, we report a case of oncogenic osteomalacia secondary to a phosphaturic mesenchymal tumor that was successfully detected by (18)F-fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG PET/CT). This case illustrates the advantages of (18)F-FDG PET/CT in detecting the occult mesenchymal tumor that causes oncogenic osteomalacia.

[FGF23 and Klotho: the new cornerstones of phosphate/calcium metabolism]

Since its first description as a phosphaturic agent in the early 2000s, fibroblast growth factor 23 (FGF23) has rapidly become the third key player of phosphate/calcium metabolism after PTH and vitamin D. FGF23 is a protein synthesized by osteocytes that acts mainly as a phosphaturic factor and a suppressor of 1α hydroxylase activity in the kidney. It inhibits the expression of type IIa and IIc sodium-phosphate cotransporters on the apical membrane of proximal tubular cells, thus leading to inhibition of phosphate reabsorption. Moreover, it also inhibits 1α hydroxylase activity. These two renal pathways account together for the hypophosphatemic effect of FGF23, but FGF23 has also been recently described as an inhibiting factor for PTH synthesis. Its exact role in bone remains to be defined. A transmembrane protein, Klotho, is an essential cofactor for FGF23 biological activity, but it can also act by itself for calcium and PTH regulation. This paper gives an overview of these recent data of phosphate/calcium physiology, as well as a description of clinical conditions associated with FGF23 deregulation (genetic diseases and chronic kidney disease). As a conclusion, future therapeutic consequences of the FGF23/Klotho axis are discussed.

A nonphosphaturic mesenchymal tumor mixed connective tissue variant of the sacrum

Tumor-induced or oncogenic osteomalacia is a rare paraneoplastic syndrome characterized by overproduction of fibroblast growth factor-23 as a phosphaturic agent and renal phosphate wasting. A range of predominantly mesenchymal neoplasms have been associated with tumor-induced osteomalacia and classified as phosphaturic mesenchymal tumor mixed connective tissues. However, phosphaturic mesenchymal tumor mixed connective tissues could be nonphosphaturic in the first stage of the disease, either because the tumors are resected early in the clinical course or because the patient's osteomalacia was attributed to another cause. This article presents a case of a 42-year-old woman with a 2-year history of low back and right leg pain. Laboratory examinations including serum and urine calcium and phosphorous were within normal values. Imaging of the lumbar spine and pelvis showed an osteolytic lesion occupying the right sacral wing. Histology was unclear. Reverse-transcription polymerase chain reaction analysis for fibroblast growth factor-23 was positive and confirmed the diagnosis of phosphaturic mesenchymal tumor mixed connective tissues. Preoperative selective arterial embolization and complete intralesional excision, bone grafting, and instrumented fusion from L4 to L5 to the iliac wings bilaterally was performed. Postoperative recovery was uneventful. Neurological deficits were not observed. A lumbopelvic corset was applied for 3 months. At 12 months, the patient was asymptomatic. Serum and urine values of calcium and phosphorous were normal throughout the follow-up evaluation.

Tumor-induced hypophosphatemic rickets in an adolescent boy--clinical presentation, diagnosis, and histological findings in growth plate and muscle tissue

CONTEXT

The mechanism behind disabling muscle weakness in tumor-induced hypophosphatemic rickets is obscure. Histological investigation of growth plate tissue of patients with tumor-induced osteomalacia has so far not been reported.

PATIENT

A mesenchymal tumor was detected in the left distal fibula by (68)Ga-DOTATOC in a 17-yr-old boy with adolescent onset of severe hypophosphatemic rickets. Disabling muscle weakness improved within days after surgery, and normal mobility was restored within months.

METHODS AND RESULTS

The resected tissue included part of the growth plate allowing immunohistochemical investigation. Positive staining of FGF23 was found in the tumor cells and in hypertrophic chondrocytes, osteoblasts, and osteoclasts of the adjacent growth plate. This distribution matched that found in growth plate tissue of a healthy control. We found positive staining for the somatostatin receptor not only in the tumor but also within the growth plate and adjacent bony tissue in the patient and the healthy control. Muscle tissue provided evidence for a partial defect in respiratory chain complexes I-IV. Biochemical markers were nearly or completely restored to normal 12 months after surgery.

CONCLUSIONS

Hypertrophic growth plate chondrocytes are a target or source of FGF23 in tumor-induced osteomalacia. Low serum phosphate, FGF23, or other factors produced by the tumor may interfere with mitochondrial function.

A 61-year-old woman with osteomalacia and a thoracic spine lesion

Phosphaturic mesenchymal tumor, mixed connective tissue variant (PMT-MCT) is a rare, largely benign, mesenchymal neoplasm almost invariably associated with oncogenic osteomalacia. It is generally found in the soft tissue and bone of the extremities. We report a case of a 61-year-old female with long-standing osteomalacia who was found to have PMT-MCT of the thoracic spine. There have been very few previously reported cases of PMT involving the spinal vertebrae and neuropathologists should be aware of this lesion. Recognition of PMT-MCT is critical for optimal patient care since complete surgical resection without additional therapy is curative.

Mesenchymal phosphaturic neoplasm in the maxillary sinus: a case report

The authors describe a case of oncogenic osteomalacia due to a mesenchymal phosphaturic tumour in the maxillary sinus. This is a paraneoplastic syndrome in which a tumour produces a peptide hormone-like substance (phosphatonin) that causes a urinary loss of phosphates resulting in a debilitating systemic condition. In this case, the patient experienced muscle stiffness, reduction of muscle tone, loss of weight and pathological fractures. Clinical and radiological examination revealed a tumour in the right maxillary sinus; all other results were negative. The diagnosis following pathology examination was mesenchymal phosphaturic tumour with a haemangiopericytoma-like vascular pattern. Different histological types of mesenchymal tumours can be associated with paraneoplastic syndrome, but their localization in the paranasal sinuses is rare. The correct diagnosis allows the appropriate therapeutic approach, which can lead to an almost immediate resolution of the clinical situation after surgical removal of the neoplasm as in the present case. Oncogenic osteomalacia is rare, particularly in the maxillofacial region, and only a few cases have been reported.

Tumor-induced osteomalacia originating from the temporal bone: a case report

BACKGROUND

Tumor-induced osteomalacia (TIO) is a rare clinical entity in which secondary osteomalacia is induced by tumor-related products. Fibroblast growth factor 23 (FGF-23) mRNA is overexpressed in the tumor tissue, leading to impaired reabsorption of phosphorus in the renal tubules and hypophosphatemia. Curative treatment is considered to be total resection of the tumor.

METHODS AND RESULTS

A 53-year-old woman had experienced systemic bone pain and muscle weakness for several years. She had refractory hypophosphatemia and marked elevation of serum FGF-23 level. Whole body imaging eventually revealed a hypervascular mass in the right temporal bone, leading to a diagnosis of TIO. She underwent skull-base surgery after embolization of the tumor. After the en bloc resection, FGF-23 became undetectable, phosphate reabsorption normalized, and all symptoms resolved.

CONCLUSIONS

We discuss the clinical features and treatment options for this rare disease.

Phosphaturic mesenchymal tumor, mixed connective tissue variant, of the mandible: report of a case and review of the literature

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome that results in renal phosphate wasting with hypophosphatemia. In most cases, the underlying cause of TIO is a small mesenchymal neoplasm that is often difficult to detect, resulting in delayed diagnosis. One such neoplasm is the phosphaturic mesenchymal tumor, mixed connective tissue variant (PMTMCT), an unusual entity with unique morphologic and biochemical features. Most of these tumors are found at appendicular sites with only rare cases reported in the jaws. We describe a PMTMCT involving the mandible in a patient with a protracted history of osteomalacia. A review of the current literature is provided with emphasis on the clinical and histologic features, etiopathogenesis, and management of PMTMCT in the setting of TIO.

Bone turnover and the osteoprotegerin-RANKL pathway in tumor-induced osteomalacia: a longitudinal study of five cases

To evaluate serum levels of osteoprotegerin (OPG), soluble receptor activator of the nuclear factor-kappaB (RANKL), and their relationship with FGF-23, lumbar bone mineral density (BMD), and bone turnover markers, five patients with tumor-induced osteomalacia (TIO) and 40 healthy controls were studied. TIO patients were followed for 360 days after surgical removal of underlying tumor (n = 2) or beginning of therapy with phosphate and calcitriol when surgical treatment was impossible (n = 3). At diagnosis, TIO patients had higher levels of FGF-23 and bone-specific alkaline phosphatase (bALP) and lower levels of cathepsin K (CathK), RANKL, and RANKL/OPG ratio compared to controls. During the follow-up, FGF-23 decreased significantly only in patients who underwent a surgical excision, while phosphate and BMD increased in all patients. The increases in BMD, phosphate, and renal phosphate reabsorption rate were directly related. In the first 60 days of follow-up, we observed a prolonged inhibition of RANKL, CathK, and bone resorption markers associated with a persistence of TIO symptoms and an increase in bALP. From day 60, levels of bone turnover markers returned progressively within the normal range and a clinical remission was observed. The inhibition of the RANKL/OPG pathway and the uncoupling of bone formation and resorption observed in patients with active TIO may be a compensatory mechanism, attempting to reduce worsening of osteomalacia. The BMD increase during TIO treatment is related to the improvement of phosphate rather than FGF-23 levels. A "hungry bone"-like syndrome was observed after surgical or pharmacological treatment.

Hypocalcemia as a presentation for multifocal osteosarcoma

We report the case of a 16-year-old male with multifocal osteosarcoma presented with symptomatic hypocalcemia. The patient presented signs of hypocalcemia accompanied by generalized bone pain and a femoral mass. Further evaluation revealed secondary hyperparathyroidism, highly elevated alkaline phosphatase levels, and generalized sclerotic and lytic lesions. Biopsy confirmed osteosarcomatosis. Despite aggressive chemotherapy, he died from progressive disease 2 months after diagnosis. The course of disease in this patient suggests that hypocalcemia reflects a poor prognosis.

Tumor-induced rickets: usefulness of MR gradient echo recall imaging for tumor localization

An 11-year-old boy presented with a femur fracture, bone hypomineralization, and hypophosphatemia, suggesting tumor-induced rickets. Conventional radiologic techniques including magnetic resonance skeletal survey did not identify a tumor. Magnetic resonance gradient echo recall imaging demonstrated a 3-cm iliac tumor, the resection of which rapidly reversed metabolic abnormalities. This technique may be useful in identifying elusive tumors associated with tumor-induced rickets.

Most osteomalacia-associated mesenchymal tumors are a single histopathologic entity: an analysis of 32 cases and a comprehensive review of the literature

Oncogenic osteomalacia (OO) is a rare paraneoplastic syndrome of osteomalacia due to phosphate wasting. The phosphaturic mesenchymal tumor (mixed connective tissue variant) (PMTMCT) is an extremely rare, distinctive tumor that is frequently associated with OO. Despite its association with OO, many PMTMCTs go unrecognized because they are erroneously diagnosed as other mesenchymal tumors. Expression of fibroblast growth factor-23 (FGF-23), a recently described protein putatively implicated in renal tubular phosphate loss, has been shown in a small number of mesenchymal tumors with known OO. The clinicopathological features of 32 mesenchymal tumors either with known OO (29) or with features suggestive of PMTMCT (3) were studied. Immunohistochemistry for cytokeratin, S-100, actin, desmin, CD34, and FGF-23 was performed. The patients (13 male, 19 female) ranged from 9 to 80 years in age (median 53 years). A long history of OO was common. The cases had been originally diagnosed as PMTMCT (15), hemangiopericytoma (HPC) (3), osteosarcoma (3), giant cell tumor (2), and other (9). The tumors occurred in a variety of soft tissue (21) and bone sites (11) and ranged from 1.7 to 14 cm. Twenty-four cases were classic PMTMCT with low cellularity, myxoid change, bland spindled cells, distinctive "grungy" calcified matrix, fat, HPC-like vessels, microcysts, hemorrhage, osteoclasts, and an incomplete rim of membranous ossification. Four of these benign-appearing PMTMCTs contained osteoid-like matrix. Three other PMTMCTs were hypercellular and cytologically atypical and were considered malignant. The 3 cases without known OO were histologically identical to the typical PMTMCT. Four cases did not resemble PMTMCT: 2 sinonasal HPC, 1 conventional HPC, and 1 sclerosing osteosarcoma. Three cases expressed actin; all other markers were negative. Expression of FGF-23 was seen in 17 of 21 cases by immunohistochemistry and in 2 of 2 cases by RT-PCR. Follow-up (25 cases, 6-348 months) indicated the following: 21 alive with no evidence of disease and with normal serum chemistry, 4 alive with disease (1 malignant PMTMCT with lung metastases). We conclude that most cases of mesenchymal tumor-associated OO, both in the present series and in the reported literature, are due to PMTMCT. Improved recognition of their histologic spectrum, including the presence of bone or osteoid-like matrix in otherwise typical cases and the existence of malignant forms, should allow distinction from other mesenchymal tumors. Recognition of PMTMCT is critical, as complete resection cures intractable OO. Immunohistochemistry and RT-PCR for FGF-23 confirm the role of this protein in PMTMCT-associated OO.

New insights into phosphate homeostasis: fibroblast growth factor 23 and frizzled-related protein-4 are phosphaturic factors derived from tumors associated with osteomalacia

PURPOSE OF REVIEW

Studies of patients with tumors associated with osteomalacia (tumor-induced osteomalacia), X-linked hypophosphatemia (XLH) and autosomal-dominant hypophosphatemic rickets have provided important new insights into the identity and mechanisms of action of factors that play a role in controlling renal phosphate excretion and serum phosphate concentrations. In the present review I discuss how these disorders may be mechanistically related to one another.

RECENT FINDINGS

Patients (or mice) with these disorders manifest rickets as a result of excessive urinary phosphate losses. Tumors associated with osteomalacia elaborate factors ('phosphatonins') that increase renal phosphate excretion and reduce serum phosphate concentrations. These factors include fibroblast growth factor (FGF) 23 and frizzled-related protein-4. Mice with XLH (Hyp) elaborate a circulating factor that induces changes in mineral metabolism similar to those in patients with tumor-induced osteomalacia. In mice and humans with XLH, a mutant enzyme, phex/PHEX, cannot degrade the phosphaturic factor. Patients with autosomal-dominant hypophosphatemic rickets produce a mutant FGF 23 that is resistant to proteolytic degradation. Excessive FGF 23 activity is associated with increased renal phosphate excretion and hypophosphatemia.

SUMMARY

In tumor-induced osteomalacia, excessive production of factors such as FGF 23 and frizzled-related protein-4 is associated with inability of endogenous proteolytic enzymes to degrade these individual substances, with resultant hyperphosphaturia, hypophosphatemia, and rickets. In XLH, mutant PHEX/phex (phosphate-regulating gene with homology to endopeptidases located on the X-chromosome) activity prevents degradation of a phosphaturic factor. In autosomal-dominant hypophosphatemic rickets, a mutant form of FGF 23 that is resistant to proteolytic degradation causes increased renal phosphate losses and hypophosphatemia.

Pseudo-(tumor-induced) rickets

An athletic 8-year-old boy developed severe muscle weakness over 2 years. At the age of 10 years, investigation for possible neuromuscular disease disclosed hypophosphatemia (1.8 mg/dl) and rickets. There was selective renal tubular wasting of inorganic phosphate (Pi) but no history of toxin exposure, familial bone or kidney disease, or biochemical evidence of vitamin D deficiency. Urine amino acid quantitation was unremarkable. Serum 1,25-dihydroxyvitamin D [1,25(OH)2D] concentration was in the lower half of the reference range. Our presumptive diagnosis was tumor-induced rickets; however, physical examination and bone scanning in search of a neoplasm were unrevealing. Soon after 1,25(OH)2D3 and Pi treatment began, muscle strength improved considerably. After 6 months of therapy, radiographic abnormalities were substantially better. During the next 6 years, physical examinations, a second bone scan, whole-body and nasal sinus magnetic resonance imaging, and octreotide scintigraphy were unremarkable. When his physes fused at the age of 16 years, assessment of his course showed excellent control of his rickets requiring decreasing doses of medication. Furthermore, fasting serum Pi levels and tubular maximum phosphorus/glomerular filtration (TmP/ GFR) values had increased steadily and normalized after 3 years of treatment. Accordingly, therapy was stopped. Seven months after stopping medication, he continues to feel completely well. Fasting serum Pi levels, TmP/GFR, other biochemical parameters of bone and mineral homeostasis, creatinine clearance, and renal sonography are normal. Neither spontaneous or pharmacologic cure of tumor-induced rickets or osteomalacia nor a patient matching ours has been reported. His disorder, which we call pseudo-(tumor-induced) rickets, should be considered when investigation for oncogenic rickets or osteomalacia discloses no causal lesion. Consequently, prolonged medical therapy and futile searches for a neoplasm may be avoided.

Hypophosphatemic rickets presenting as recurring pedal stress fractures in a middle-aged woman

Stress fractures frequently occur from overtraining. When stress fractures recur, underlying metabolic abnormalities should be ruled out. We report a middle-aged woman in whom such an evaluation demonstrated previously undiagnosed hypophosphatemic rickets after she presented with recurring stress fractures in her feet. Treatment with phosphate and calcitriol was associated with clinical improvement that would likely not have occurred without this intervention. Any patient with recurring stress fractures should be evaluated with several screening laboratory tests, metabolic bone x-rays, and a measurement of bone mineral density.

Tumor-induced osteomalacia and the regulation of phosphate homeostasis

Tumor-induced osteomalacia (TIO) is a rare and unique syndrome characterized by hypophosphatemia, excessive urinary phosphate excretion, reduced 1,25-dihydroxyvitamin D concentrations, and osteomalacia. Removal of the tumor is associated with a cure of the lesion. Several laboratories have now shown that conditioned medium derived from cultures of such tumors contain a small, heat-sensitive substance ("phosphatonin") of <25,000 daltons that specifically inhibits sodium-dependent phosphate transport in cultured renal proximal tubular epithelia. This substance does not increase cyclic adenosine monophosphate (cAMP) formation in tubular epithelial cells and does not increase cAMP excretion in urine. A substance with similar properties is present in the circulation of patients on hemodialysis. A syndrome with a remarkably similar biochemical phenotype, namely, X-linked hypophosphatemic rickets (XLH), also has a circulating factor with properties similar, if not identical, to those of the tumor-derived factor, "phosphatonin." The molecular defect in XLH has been shown to be due to a mutant endopeptidase, PHEX, whose substrate might be "phosphatonin." Hypophosphatemia and other biochemical abnormalities in TIO are due to excessive production of "phosphatonin" with normal PHEX function, whereas the biochemical abnormalities in XLH are caused by a mutant PHEX enzyme that fails to process "phosphatonin."