Tumor-induced osteomalacia

Phosphaturic mesenchymal tumor: management and outcomes of ten patients treated at a single institution

BACKGROUND

Phosphaturic mesenchymal tumor (PMT) is a rare tumor that causes tumor-induced osteomalacia. Patients present with non-specific symptoms secondary to renal phosphate wasting and decreased bone mineralization. We sought to assess: (1) What are the common presenting features, laboratory and imaging findings, histologic findings of phosphaturic mesenchymal tumors? (2) What are the available treatment strategies for phosphaturic mesenchymal tumors and their long-term outcomes in terms of local recurrence and symptom control after treatment?

METHODS

We retrospectively identified patients with a histologic diagnosis of PMT located in the axial or appendicular skeleton, or surrounding soft tissues. A total of 10 patients were finally included in our study.

RESULTS

Median tumor size was 1.9 cm (range, 1.1 to 6.1) and median time from symptom onset to diagnosis was 3 years (range, 0.5 to 15 years). All patients but one presented with hypophosphatemia (median 1.9 mg/dL, range 1.2 to 3.2). Pre-operative FGF-23 was elevated in all cases (median 423.5 RU/mL, range 235 to 8950). Six patients underwent surgical resection, three were treated percutaneously (radiofrequency ablation or cryoablation), and one refused treatment. Only one patient developed local recurrence and no patients developed metastatic disease. At last follow-up, nine patients showed no evidence of disease and one was alive with disease.

CONCLUSION

Phosphaturic mesenchymal tumor is a rare tumor presenting with non-specific symptoms. Surgery is the standard treatment when negative margins can be achieved without significant morbidity. In patients with small tumors in surgically-inaccessible areas, radiofrequency ablation or cryoablation can be performed successfully.

Long-Term Follow-Up Data of Tumor-Induced Osteomalacia Managed with Surgery and/or Radiofrequency Ablation from a Single Center

Data on radiofrequency ablation (RFA) in tumor-induced osteomalacia (TIO) are restricted to case reports (~ 11 patients) and long-term follow-up data are further scarce. We describe our experience on managing TIO from a tertiary care center in India. Retrospective study of patients with localized TIO was performed and clinical, biochemical, treatment and follow-up details were retrieved. Normalization of serum phosphorus in absence of phosphate supplementation was defined as remission. Of 33 patients (23 males), 24 patients underwent surgery as first-line treatment, and early remission, delayed remission (> 1 month for phosphorus normalization) and persistence were observed 12, 3, and 9 patients at a median follow-up of 5 (4-9) years. The gender, age, tumor size, location of tumors and FGF23 levels were not statistically different in patients who were in remission after surgery versus those with persistent disease. Second/third line treatment included conventional medical treatment and/or repeat surgery (n = 3), radiotherapy (n = 3), peptide receptor radionuclide therapy (n = 1), RFA (n = 1). Two patients had transient worsening (weeks) of weakness post-surgery. 10 patients underwent RFA (first-line n = 9); at the last follow-up 5 (4-10) years, 7 are in remission. Two of three persistent disease patients had large tumors (5.6 and 3.6 cm). There were no RFA-related complications except local ulcer in one. Although persistent disease was present in a few patients in both arms, there was no recurrence in either RFA or surgical cohort. RFA provide durable response similar to surgery, persistence requires multi-modality treatment.

Challenges in the diagnosis and management of tumor-induced osteomalacia: A case report

The present case report is aimed to highlight the difficulty and the reason for the delayed diagnosis of phosphaturic mesenchymal tumors, emphasizing the need of standardized protocols for diagnosis, surgery and follow-up in high-volume hospitals. The clinical signs and symptoms, diagnostic and therapeutic procedures, immunohistological features were analyzed. Delayed diagnosis of phosphaturic mesenchymal tumor was primarily due to non-specific clinical symptoms such as fatigue, muscular and bone pain, and multiple fractures. This cryptic clinical picture made the diagnosis tricky that led to treatment of patient for non-specific pain and stress fractures before to consider the tumor-induced osteomalacia syndrome. Some well-documented studies were found in the literature in which the history of trauma is a critical trigger of glomus tumors. Extra-subungual tumors most frequently occur in the knee and ankle regions, particularly among young adults, and the diagnosis is typically made approximately 7.2 years after initial symptom onset. The difficult tumor localization represented an additional obstacle to the prompt treatment, leading to delayed curative surgery.

18F-AlF-NOTA-octreotide PET/CT in the localization of tumor-induced osteomalacia: case series and literature review

Introduction

This study explores tumor-induced osteomalacia (TIO) through a case series and literature review, assessing the diagnostic potential of 18F-AlF-NOTA-octreotide (18F-OC) positron emission tomography/computed tomography (PET/CT).

Methods

We analyzed TIO patients who underwent 18F-OC PET/CT. Parameters such as tumor dimension, the maximum standardized uptake value (SUVmax), the mean standardized uptake value (SUVmean) and metabolic tumor volume (MTV) were meticulously assessed. Clinical features and imaging characteristics pertinent to TIO were reviewed.

Results

6 patients with clinical suspicion of TIO exhibited hypophosphatemia (0.25 to 0.64 mmol/L), elevated alkaline phosphatase (ALP) levels (142 to 506 U/L), and increased parathyroid hormone (PTH) levels (92.9 to 281.7 pg/mL). Of these patients, two underwent FGF-23 testing, with results of 3185.00 pg/ml and 17.56 pg/ml, respectively. Conventional imaging modalities depicted widespread osteoporosis, with several cases demonstrating fractures indicative of osteomalacic and associated pathological fractures. Subsequent 18F-OC PET/CT facilitated the accurate localization of causative tumors, with histopathological examination confirming the diagnosis of phosphaturic mesenchymal tumor (PMT). The interval from initial clinical presentation to definitive TIO diagnosis spanned approximately 2.5 years (range: 1 - 4 years), with tumors varying in size (maximum diameter: 7.8 to 40.0 mm), SUVmax (5.47 to 25.69), SUVmean (3.43 to 7.26), and MTV (1.27 to 18.59 cm3).

Conclusion

The implementation of whole-body 18F-OC PET/CT imaging emerges as a critical tool in the identification of occult tumors causing TIO. Future investigations incorporating a broader cohort are imperative to further delineate the diagnostic and therapeutic implications of 18F-OC PET/CT in managing TIO.

Tumor-induced osteomalacia: A systematic literature review

Introduction

Tumor-induced osteomalacia (TIO), is a rare acquired paraneoplastic syndrome characterized by defective bone mineralization, caused by the overproduction of fibroblast growth factor 23 (FGF23) by a tumor.

Material and methods

We conducted a systematic review to identify all case reports of TIO, focusing on those associated with mesenchymal tumors. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) consensus, and we included patients with a diagnosis of TIO and histological confirmation of phosphaturic mesenchymal tumors or resolution of the condition after treatment of the tumor. Bibliographical searches were carried out until December 2023 in the Cochrane Library, Medline and Embase, as well as congress abstracts online.

Results

We identified 769 articles with 1979 cases reported. Most patients were adults, with a higher incidence on men. Disease duration before diagnosis is a mean of 4.8 years. Most tumors were histologically classified as PMT. Lower limbs were the predominant location. Hypophosphatemia was present in 99.8 % of patients. The FGF23 was elevated at diagnosis in 95.5 %. Resection of the tumor was the treatment of choice in most of patients. After resection, there was a clinical improvement in 97.6 % of cases, and serum phosphorus and FGF23 levels returned to normal ranges in 91.5 % and 81.4 % of the patients, respectively.

Conclusion

TIO is usually misdiagnosed with rheumatological or musculoskeletal disorders. The diagnosis should be suspected in patients with hypophosphatemic osteomalacia, and the measurement of serum FGF23 can be useful for diagnosis and management.

Phosphaturic mesenchymal tumor: two cases highlighting differences in clinical and radiologic presentation

Phosphaturic mesenchymal tumors are rare, usually benign neoplasms that occur in the soft tissue or bone and are the cause of nearly all cases of tumor-induced osteomalacia. Tumor-induced osteomalacia due to phosphaturic mesenchymal tumor is a challenging diagnosis to make-patients present with variable clinical and radiologic findings and the culprit neoplasm is often small and can occur anywhere head to toe. We present two cases of phosphaturic mesenchymal tumor in the scapular body and plantar foot. In both cases, the patient endured years of debilitating symptoms before a tissue diagnosis was eventually reached. Descriptions of clinical presentation, laboratory workup, surgical resection, and imaging characteristics, with a focus on CT, MRI, and functional imaging, are provided to assist with the diagnosis and management of this rare entity. A brief review of current literature and discussion of the differential diagnoses of phosphaturic mesenchymal tumor is also provided.

Spinal phosphaturic mesenchymal tumors: a rare etiology causing tumor-induced osteomalacia-a review of experience at a UK tertiary referral center and literature review

PURPOSE

This article aims to provide a comprehensive review of the management challenges associated with Spinal Phosphaturic Mesenchymal tumors (PMTs) and evaluates the surgical management outcomes for this rare entity linked to Tumor-induced osteolysis. The primary objective of this study is to enhance the familiarity of treating physicians with the clinical features, diagnosis, and treatment options for Spinal PMTs.

METHODS

A retrospective analysis was conducted, reviewing electronic medical records of patients diagnosed with spinal PMTs at our hospital between January 2019 and December 2022. The data collected included demographic information, clinical presentation, radiological findings, surgical details, and follow-up outcomes.

RESULTS

A total of three cases of Spinal PMTs causing Tumor-induced osteomalacia were identified. The diagnosis of Spinal PMTs presented challenges, with incidental detection often occurring during routine imaging. Surgical management was undertaken, resulting in successful symptom resolution and normalization of phosphate levels. The application of 68 Ga-DOTA-TATE PET/CT scans facilitated tumor localization, aiding in surgical planning. Spinal PMTs demonstrated a favorable response to surgical intervention.

CONCLUSION

Spinal PMTs play a significant role in Tumor-induced osteolysis, warranting timely and accurate diagnosis. Although diagnosing Spinal PMTs presents challenges, surgical management has proven to yield favorable outcomes, effectively alleviating symptoms and restoring phosphate levels. A multidisciplinary approach and continued vigilance are essential in ensuring early diagnosis, effective treatment, and long-term monitoring for patients affected by spinal PMTs.

Treatment and Diagnose of Spinal Phosphaturic Mesenchymal Tumor: A Case Report and a Systematic Literature Review

BACKGROUND

Spinal phosphaturic mesenchymal tumor (PMT) is a rare disorder but can be cured once the diagnosis is clear and a complete removal by surgery is performed. To the best of our knowledge, only 22 cases in the spine have been described, and we report a case with the largest number of spinal segments (T12-L5) affected among spine PMT cases.

METHODS

A comprehensive literature search was performed until May 23, 2023, following the Preferred Reporting Items for Systematic Reviews guidelines. Studies were chosen through relevant PubMed, Web of Science, and EMBASE searches to prioritize obtaining the largest studies. The Medical Subject Headings and Boolean operators employed for this search were ("PMT" or "TIO" or "Tumor-induced osteomalacia" or "phosphaturic mesenchymal tumor") and ("spine" or "spinal"). Two researchers (L.S.Z. and D.B.C) independently reviewed and evaluated the included articles. Any differing opinions were discussed until a consensus was reached. A total of 18 studies were included. A case report is also presented.

RESULTS

We report a case of spinal PMT. The full text of the relevant articles was construed. A total of 18 studies were reviewed and consolidated. These articles are roughly divided into the following 5 subcategories: 1) clinical features and baseline distribution, 2) laboratory and imaging findings, 3) pathological manifestations, and 4) surgical methods and treatment options.

CONCLUSIONS

Spinal PMT is very rare with a high rate of misdiagnosis and debilitating complications, so it is of significance to increase awareness of the disease among spine surgeons consulted by patients with spinal PMT. 68Ga-DOTATOC-PET/CT shows very high sensitivity to the spinal PMT but there is no way to exactly determine the location of the tumor. PMT has unique immunohistochemical characteristics and malignant PMT is rare. Once diagnosed, complete surgical excision is the recommended treatment. Burosumab is one of the available options, especially in cases that are recurrent and difficult to surgically resect.

Phosphaturic mesenchymal tumor: Clinicopathological features with outcomes in 10 patients with review of literature

BACKGROUND

Phosphaturic mesenchymal tumors (PMTs) are rare mesenchymal tumors, associated with long-standing, non-specific but often debilitating symptoms in the affected patients. These tumors display characteristic histopathological features and in case, identified timely, can be a boon for patients, given an excision is completely curative.

AIMS

To evaluate the clinical and histopathological features of 10 PMTs, diagnosed at our institution, along with clinical outcomes in those patients.

MATERIALS AND METHODS

This was a retrospective study, wherein 10 PMTs, diagnosed from January 2013 to July 2022, were included.

RESULTS

The average age at the time of diagnosis was 40 years with an M:F ratio of 4:1. Clinical features included lumps, weakness, bone pain, difficulty in moving and walking, and pathologic fractures. The biochemical analysis showed normal serum calcium levels (average = 9.5 mg/dL), with low serum phosphorus (average = 2.2 mg/dL) and raised serum fibroblast growth factor 23 (FGF23) levels, in all the cases, wherever available. On histopathology, all tumors showed cells arranged in a hemangiopericytomatous pattern, including oval to short spindle forms. Multinucleate giant cells were present in nine tumors, and characteristic "grungy calcifications" was observed in eight tumors. Prominent pseudo cystic spaces were seen in eight tumors. A significant number of mitotic figures and tumor necrosis were not seen in any tumor. In five cases where follow-up was available, there was complete resolution of symptoms post-resection with no recurrence or metastasis. All those patients were free of disease until the last follow-up.

CONCLUSION

This constitutes the first largest comprehensive study on these rare tumors from our country. PMTs can be diagnosed based on certain histopathological features and correlation with clinicoradiological and biochemical findings. These are invariably benign neoplasms. Patients are relieved of their debilitating symptoms after adequate surgical tumor resection. Therefore, their correct and timely diagnosis is crucial.

Preoperative evaluation and orthopedic surgical strategies for tumor-induced osteomalacia

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Functional Classification of Fusion Proteins in Sarcoma

Sarcomas comprise a heterogeneous group of malignant tumors of mesenchymal origin. More than 80 entities are associated with different mesenchymal lineages. Sarcomas with fibroblastic, muscle, bone, vascular, adipocytic, and other characteristics are distinguished. Nearly half of all entities contain specific chromosomal translocations that give rise to fusion proteins. These are mostly pathognomonic, and their detection by various molecular techniques supports histopathologic classification. Moreover, the fusion proteins act as oncogenic drivers, and their blockade represents a promising therapeutic approach. This review summarizes the current knowledge on fusion proteins in sarcoma. We categorize the different fusion proteins into functional classes, including kinases, epigenetic regulators, and transcription factors, and describe their mechanisms of action. Interestingly, while fusion proteins acting as transcription factors are found in all mesenchymal lineages, the others have a more restricted pattern. Most kinase-driven sarcomas belong to the fibroblastic/myofibroblastic lineage. Fusion proteins with an epigenetic function are mainly associated with sarcomas of unclear differentiation, suggesting that epigenetic dysregulation leads to a major change in cell identity. Comparison of mechanisms of action reveals recurrent functional modes, including antagonism of Polycomb activity by fusion proteins with epigenetic activity and recruitment of histone acetyltransferases by fusion transcription factors of the myogenic lineage. Finally, based on their biology, we describe potential approaches to block the activity of fusion proteins for therapeutic intervention. Overall, our work highlights differences as well as similarities in the biology of fusion proteins from different sarcomas and provides the basis for a functional classification.

Approaching virtual osteoid volume estimation and in-depth tissue characterization in patients with tumor-induced osteomalacia

Tumor-induced osteomalacia (TIO) poses a significant diagnostic challenge, leading to increased disease duration and patient burden also by missing clinical suspicion. Today, diagnosis of osteomalacia relies on invasive iliac crest biopsy, if needed. Therefore, a noninvasive method would be beneficial for patients with severe osteomalacia, such as TIO, to inform their clinical management and address specific needs, like estimating the regeneration capacity at high osteoid volumes (OVs) or the potential of a hungry bone syndrome after tumor removal. Furthermore, given the lack of comprehensive histological characterization of TIO, there is a need for additional tissue characterization. Therefore, our assessment encompassed iliac crest biopsies that were examined using quantitative electron backscattered microscopy, Raman spectroscopy, micro-computed tomography, and histology to analyze the biopsy tissue. Our clinical assessment encompassed DXA and high-resolution peripheral quantitative computed tomography (HR-pQCT) alongside with biochemical analyses and clinical evaluations. Combining imaging and clinical data, we established a model to predict the OV. We compared 9 TIO patients with 10 osteoporosis (OPO) patients and 10 healthy controls. Histological analyses confirmed a pronounced OV in TIO patients (OPO: 1.20% ± 1.23% vs TIO: 23.55% ± 12.23%, P < .0005), and spectroscopy revealed lower phosphate levels in TIO biopsies. By combining HR-pQCT and laboratory diagnostics, we developed a linear regression model to noninvasively predict the OV revealing significantly higher modeled OV/BVmodel values of 24.46% ± 14.22% for TIO compared to the control group (5.952% ± 3.44%, P ≤ .001). By combining laboratory diagnostics, namely, ALP and Tt.BMDRadius measured by HR-pQCT, we achieved the calculation of the virtual osteoid volume to bone volume ratio (OV/BVmodel) with a significant correlation to histology as well as reliable identification of TIO patients compared to OPO and control. This novel approach is potentially helpful for predicting OV by noninvasive techniques in diagnostic procedures and improving the clinical management of TIO.

Tumor-induced osteomalacia: An overview

Tumor-induced osteomalacia (TIO) is rare paraneoplastic syndrome of hypophosphatemic osteomalacia, caused by phosphaturic factors secreted by small mesenchymal origin tumors with distinct pathological features, called 'phosphaturic mesenchymal tumors'. FGF23 is the most well-characterized of the phosphaturic factors. Tumors are often small and located anywhere in the body from head to toe, which makes the localisation challenging. Functional imaging by somatostatin receptor-based PET imaging is the first line investigation, which should be followed with CT or MRI based anatomical imaging. Once localised, complete surgical excision is the treatment of choice, which brings dramatic resolution of symptoms. Medical management in the form of phosphate and active vitamin D supplements is given as a bridge to surgical management or in inoperable/non-localised patients. This review provides an overview of the epidemiology, pathophysiology, pathology, clinical features, diagnosis, and treatment of TIO, including the recent advances and directions for future research in this field.

Phosphaturic Mesenchymal Tumor in the Proximal Femur Presenting as Tumor-induced Osteomalacia: A Case Report and Literature Review

Introduction

An uncommon medical disorder known as tumor-induced osteomalacia (TIO) is characterized by severe hypophosphatemia, renal phosphate wasting, and osteomalacia due to a tumor. TIO has recently been linked to a particular kind of tumor known as phosphaturic mesenchymal tumor (PMT). PMTs release phosphatonins, such as fibroblast growth factor-23 (FGF23), which elevates serum levels of FGF23, leading to phosphate wasting and osteomalacia. However, due to their infrequent occurrence and vague symptoms, such as bone pain, myopathies, arthralgias, fractures, and weakness, the diagnosis of PMTs is often delayed or misdiagnosed. In this case report, a rare case of PMT in the proximal femur resulted in TIO, and it highlights the long and difficult journey from symptom onset to correct diagnosis and successful surgical management.

Case Report

A 51-year-old woman endured persistent joint pain, muscle weakness, and fatigue for 2 years. Despite having no known health issues, she suffered from hip pain that spreads to her knees and ankles, and tingling and paresthesia in her legs, making it difficult to bear weight. She underwent surgery to remove a parathyroid adenoma, but unfortunately, her symptoms returned. Her magnetic resonance imaging revealed a lesion in her proximal femur, which was promptly removed. The tissue examination results verified the identity of the tumor as a PMT. The patient's phosphorus levels returned to normal and after a year of follow-up, she was able to resume normal daily activities, bear weight on the affected limb and showed no signs of the tumor recurrence.

Conclusion

Adult patients experiencing bone pain, progressive weakness, and multiple fractures with no family history of similar conditions should consider TIO as a potential cause. It is rare and often misdiagnosed and complete surgical removal of the tumor is the optimal treatment for TIO, resulting in the resolution of long-standing symptoms and biochemical abnormalities. Timely recognition, localization, and surgical removal of the tumor are crucial for symptom resolution and the restoration of normal bone mineralization.

Prevalence of FGF23 elevation in patients with hypophosphatemia

BACKGROUND AND AIMS

To investigate the contribution of FGF23 in explaining the cases of hypophosphatemia observed in clinical practice, we aimed to determine for the first time the prevalence of FGF23 elevation in patients with hypophosphatemia and to describe the different mechanisms of FGF23-related hypophosphatemic disorders.

MATERIALS AND METHODS

We performed a prospective, observational, multicenter, cohort study of 260 patients with hypophosphatemia. Blood measurements (PTH, 1,25-dihydroxyvitamin D, bone alkaline phosphatase, 25-hydroxyvitamin D, and FGF23) were performed on a Liaison XL® (DiaSorin) analyzer.

RESULTS

Primary elevation of FGF23 (>95.4 pg/mL) was reported in 10.4% (95CI: 7.0-14.7) of patients (n = 27) with hypophosphatemia, suggesting that at least 1 in 10 cases of hypophosphatemia was erroneously attributed to an etiology other than FGF23 elevation. Patients with elevated blood FGF23 were grouped according to the etiology of the FGF23 elevation. Thus, 10 patients had a renal pathology, chronic kidney disease or post-renal transplantation condition. The remaining patients (n = 17) had the following etiologies: malignancies (n = 9), benign pancreatic tumor (n = 1), post-cardiac surgery (n = 4), cirrhosis (n = 2), and chronic obstructive pulmonary disease (n = 1).

CONCLUSION

In order to improve patient management, it seems essential to better integrate plasma FGF23 measurement into the routine evaluation of hypophosphatemia.

Prolonged generalized osteomalacia associated with a sinonasal cavity phosphaturic mesenchymal tumor: A case report

Phosphaturic mesenchymal tumor (PMT) is a rare disorder primarily affecting the extremities. It is notable for its correlation with hypophosphatemic osteomalacia and high FGF23 serum levels, which results in renal phosphate wasting and clinical symptoms associated with low serum phosphorus. We presented a patient with a 5-year history of progressive osteomalacia who recently experienced a major pathological bone fracture. Laboratory findings showed a persistent low serum phosphate, normal calcium, elevated alkaline phosphatase activity, high parathyroid hormone levels, and increased renal excretion of phosphate. According to ultrasonography and nuclear imaging, there was no evidence of parathyroid adenoma. During further diagnostic assessment, a sinonasal cavity tumor was found and resected. Histologically, the tumor was composed of bland spindle cell proliferation in the background of a calcified matrix with foci of osteoid formation, hemangiopericytoma-like (HPC-like) vasculature, and osteoclast-like giant cells. Tumor cells showed variable positivity for SMA, but CD34, S100, CD99, Melan-A, p63, and desmin were all nonreactive. Regarding the clinical context, histological and immunohistological findings, a final diagnosis of tumor-induced osteomalacia (TIO) secondary to a PMT was made. After surgery, laboratory results returned to normal, clinical symptoms disappeared, and the patient did not experience a recurrence during a six-month follow-up.

A case of hyperparathyroidism secondary to tumor-induced osteomalacia

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

Epidemiology of Tumor-Induced Osteomalacia in Germany Based on Real World Data

Tumor-induced osteomalacia (TIO) is an ultra-rare disease caused mostly by benign tumors that secrete fibroblast growth factor-23. Because of nonspecific symptoms, the diagnostic delay is long, and therapy can be challenging. Moreover, epidemiological data on TIO are scarce owing to its rarity. Therefore, this study aimed to quantify TIO's incidence rates and prevalence in Germany. Retrospective longitudinal and cross-sectional analyses were conducted using anonymized German claims data from the statutory health insurance (SHI) database. This database, which comprises the data of approximately 5 million insurants, is a representative sample of the German population and supports national projections. As there is no unique International Statistical Classification of Diseases and Related Health Problems (ICD) code for TIO, operational categories based on different surrogates were defined to determine the prevalence and incidence rates of TIO among probable patients. This study showed that TIO has a prevalence of (documented code, advanced imaging, medication, or tumor removal) 0.187 per 100,000 persons and an incidence rate of ≤ 0.094 per 100,000 person years. This analysis provides the first epidemiological insight into German patients with TIO. Despite the general limitations associated with the analysis of SHI claims data of ultra-rare diseases, we believe that this analysis provides a sound basis for further analysis, particularly with regard to the care situation of patients with TIO.

Tumor-induced Osteomalacia in a Boy with Maxillary Ossifying Fibroma

Tumor-induced osteomalacia (TIO) is a rare, paraneoplastic disorder of hypophosphatemia associated with elevated tumor-produced fibroblast growth factor 23 (FGF23). Maxillofacial tumors are rarely involved in TIO, especially maxillary TIO in children. We present a 14-year-old boy with osteomalacia and high serum levels of FGF23, a hormone associated with decreased phosphate resorption, due to a maxillary tumor. The patient was treated with oral phosphorus and calcitriol, and surgical removal of the tumor was performed. After 21 months follow-up, he was pain free and had returned to full activity. We review the reported pediatric cases of TIO in the maxillofacial and oral region and discuss the management of these patients considering the published evidence.

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.

Diagnosis and management of tumor-induced osteomalacia: a single center experience

PURPOSE

The aim of this study is to review the clinical and laboratory characteristics, diagnostic and treatment modalities of tumor-induced osteomalacia (TIO) cases managed in a single center.

MATERIAL METHODS

Demographic and clinical features, biochemical findings, diagnostic procedures, treatment modalities, and outcomes of nine patients who had the diagnosis of TIO were reviewed retrospectively.

RESULTS

Mean age of the study group (F/M: 4/5) was 45.8 ± 10.8 years, and mean time from the onset of symptoms to diagnosis was 4.7 ± 2.8 years. The clinical manifestations were muscle weakness and difficulty in walking (8/9), hip pain (3/9), multiple fractures (2/9), stress fracture (2/9). Mean plasma phosphorus concentration was 1.28 ± 0.4 mg/dl at presentation. We performed radionuclide imaging modalities (18F-FDG PET/CT, Ga68-DOTATATE PET/CT, octreotide scintigraphy) in seven of nine patients, and tumor was detected in all. Lower extremity (n = 6; %67), head region (n = 2; %22) and thorax (n = 1; %11) were the tumor locations of our cases. Eight patients underwent surgery and remission was achieved postoperatively in all of the operated patients and plasma phosphorus level normalized in 4 ± 2 days. Pathological examination revealed mesenchymal tumors with different subtypes. Recurrence occurred in three patients at 13 ± 10.5 months after the first surgery. Two patients were reoperated and radiotherapy was also performed in one of them.

CONCLUSION

Hypophosphatemia necessitates careful evaluation for the etiology. TIO is one of the important causes of adult-onset hypophosphatemic osteomalacia. Diagnosis of TIO is essential because the laboratory and clinical findings resolve after appropriate treatment.

Sinonasal phosphaturic mesenchymal tumour: radiation oncologist's perspective

Tumour-induced osteomalacia is a rare cause of osteomalacia, the majority of which is of mesenchymal origin. Oncogenic osteomalacia is a potentially curable condition caused by phosphaturic mesenchymal tumours. We present the case of a woman in her 30s with a sinonasal phosphaturic mesenchymal tumour, treated with surgical excision followed by adjuvant intensity-modulated radiotherapy and subsequent adjuvant chemotherapy. The patient experienced minimal adverse effects during radiation. There was good local control and cosmetic outcomes with no radiation-related toxicity at a follow-up period of 32 months.

Oncogenic Osteomalacia: Challenges in Diagnosis

To report a case of osteomalacia induced by a mesenchymal tumour in the head and neck region, in view of its rarity and classical late diagnosis. To review the literature on the usage of fluorodeoxyglucose-positron emission tomography-computed tomography (FDG PET-CT) and octreotide scanning in the localisation of the culprit tumour. An elderly male presented with a 7-year history of chronic muscle pain and weakness, to the extent of functional disability. FDG PET-CT was done which showed uptake in the region of the right anterior ethmoids. Endoscopic excision of the mass was done. However, the patient did not improve significantly. Subsequently, a DOTA-1-NaI3-octreotide (DOTANOC) scan was done which revealed a tumour in the region of the right medial rectus, excision of which was done. This time, the patient improved clinically and biochemically. The histopathology was phosphaturic mesenchymal tumour. A steady but definitive symptomatic improvement was noted in the postoperative period along with reversal of the deranged biochemical parameters, confirming the diagnosis of oncogenic osteomalacia. Octreotide-based PET-CT seems to be the most sensitive imaging modality in localising the tumours that cause oncogenic osteomalacia. However, FDG-based PET-CT still would be a good choice in centres where SSTR-based imaging facilities are not available.

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.

Unusual phosphaturic mesenchymal tumor mimicking osteoid osteoma

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

Hypophosphatemia in Patients With Multiple Myeloma

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

Imaging characteristics of phosphaturic mesenchymal tumors

BACKGROUND

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

PURPOSE

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

MATERIAL AND METHODS

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

RESULTS

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

CONCLUSION

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

Paraneoplastic musculoskeletal disorders: review and update for radiologists

Rheumatic paraneoplastic syndromes are rare syndromes that occur at distant sites from the underlying tumor and may involve the bones, joints, fasciae, muscles, or vessels. In the absence of a known tumor, early recognition of a rheumatic syndrome as paraneoplastic permits dedicated work-up for, and potentially early treatment of an occult malignancy. Although there is a continuously growing list of paraneoplastic rheumatic disorders, not all of these disorders have a well-established association with a neoplastic process. The goals of this article are to review the clinical characteristics, diagnostic work-up, and imaging findings of well-documented rheumatic paraneoplastic disorders.

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

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

A diagnostic challenge of mysterious bone pain caused by tumor-induced osteomalacia with multiple tumors: a case report

Background

Tumor-induced osteomalacia (TIO) is a rare, tumor-induced, metabolic bone disorder, the exact incidence of which is unknown. The most common cause of TIO is hypersecretion of tumor-derived fibroblast growth factor 23 (FGF23). Surgical resection can cure TIO in most cases, while for patients with TIO who are ineligible for surgery, biologic antibodies targeting FGF23 can be used as treatment. However, the diagnosis of TIO is more difficult than its treatment as the initial presentation can be misleading or nonspecific; thus, diagnosing TIO remains a clinical challenge.

Case Description

Herein, we present a case of TIO originating from the nasal cavity neoplasm in which the patient also had a rare, thymic-derived, tumorous lesion. A diagnosis of osteoporosis was subsequently made, and a disorder of phosphorus metabolism was discovered. After determining that the patient was exhibiting signs of TIO, we used gallium-68 dotatate positron emission tomography/computed tomography (⁶⁸Ga-DOTATATE PET/CT) to locate the tumor position.

Conclusions

This case report emphasizes the importance of electrolyte testing, which is potentially helpful for quickly identifying the presence of disorders of phosphorus metabolism in suspected patients. Subsequently, appropriate imaging techniques (e.g., ⁶⁸Ga-DOTATATE PET/CT) should be used to identify potential TIO lesions. Most patients with TIO can be treated successfully following diagnosis.

Keywords

Tumor-induced osteomalacia (TIO); gallium-68 dotatate positron emission tomography/computed tomography (⁶⁸Ga-DOTATATE PET/CT); phosphaturic mesenchymal tumor (PMTs); weakness; case report.

Tumor induced osteomalacia from a peripheral mesenchymal tumour of the foot

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

Sphenoid sinus is a rare site for tumor-induced osteomalacia: A case report and literature review

BACKGROUND

In this paper, we present a rare case of tumor-induced osteomalacia (TIO) and a literature review of this rare disease.

METHODS

A case of TIO of the isolated sphenoid sinus was reported. Furthermore, the clinical features of TIO in the sphenoid sinus and other sinonasal sinuses were also reviewed and summarized.

RESULTS

A 35-year-old man with muscle weakness and lower back pain came to the Department of Neurology. No obvious neurological disease was found; however, magnetic resonance imaging of the extremities accidentally showed a tumor in the axilla. Bone scintigraphy showed suspicious bone metastasis. Hypophosphatemia was neglected. Interestingly, 2-deoxy-2-[fluorine-18]fluoro-d-glucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) detected a tumor in the axilla and another in the sphenoid sinus, but only the tumor in the sphenoid sinus had somatostatin receptor (SSTR) expression in 68-gallium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid octreotate (Ga-68 DOTATATE) PET/CT. The sphenoid sinus tumor was proven to be a phosphaturic mesenchymal tumor (PMT), and the phosphate levels returned to normal after surgery. The literature review showed only 17 cases of TIOs that occurred in the sphenoid sinus, with an average age of 43.3 ± 13.7 years. Only three cases of TIOs in the sphenoid sinus did not invade the nasal cavity or other paranasal sinuses, which could be identified as isolated sphenoid sinus diseases. We compared the clinical features of sphenoid TIOs with those of non-sphenoid sinonasal TIOs, and it was found that the concentration of 1,25-dihydroxy vitamin D in the group with sphenoid TIOs was much higher than that in the group with non-sphenoid sinonasal TIOs. A total of 153 cases of TIOs in the sinonasal sinus were reviewed. The ethmoid sinus was found to be the major site (64.7%), followed by the nasal cavity (50.3%), maxillary sinus (19.0%), frontal sinus (16.4%), and sphenoid sinus (11.8%). There were 66 patients (43.1%) who showed tumors invading more than one sinus. Most of the tumors (69.3%) were diagnosed as PMTs by pathology, followed by hemangiopericytoma (14.3%). Immunostaining was beneficial in the differential diagnosis of these tumors; however, larger sample sizes are needed for better accuracy.

CONCLUSION

TIO in the sinonasal sinus, especially in the sphenoid sinus, is rare. Moreover, isolated sphenoid sinus disease can be easily misdiagnosed. When the clinical manifestation of osteomalacia is atypical, associating it with sphenoid sinus disease is even more difficult. Thus, TIO in the sphenoid sinus needs further exploration.

Misdiagnosis and Mistreatment of a Rare Case of Intracranial Oncogenic Osteomalacia with an Altered Amino Acid Profile

Background. Oncogenic osteomalacia (OO), also known as tumor-induced osteomalacia (TIO), is a rare paraneoplastic syndrome caused by mesechymal tumors secreting fibroblast growth factor 23 (FGF23). Common in middle age, these tumors are often disclosed by progressive generalized bone pain and muscle weakness, along with an altered biochemical profile. Despite its characteristic presentation, the disease is often underrecognized with delayed onset of surgical or pharmacological intervention that can have serious repercussions on the patients' health and quality of life. Case presentation. We describe the case of a 65-year-old Caucasian man presenting TIO with intracranial and spinal localizations and Fanconi-like aminoaciduria. The condition was misdiagnosed and mistreated for three years, leading to loss of self-sufficiency and depression. Following proper identification, the spinal mass was excised with complete remission of the functional symptoms. As it was not possible to remove the intracranial lesion, the patient was treated conservatively with calcitriol and phosphorous supplements that granted good metabolic control up to the time of a recent follow-up visit (at 5 years). Conclusions. The finding of an altered amino acid profile, not usually reported in these cases, should prompt clinicians to a wider usage of these molecules as suitable candidates for metabolic diseases. In addition to providing central information, they are easy to obtain and inexpensive to analyze. Such determination could help to speed up the diagnostic process, as a long-lasting history of misdiagnosis and mistreatments can lead primarily to clinical worsening, but also to the use of expensive, useless medications with side effects that contribute to poor patient health.

Tumour-induced osteomalacia: a rare cause of chronic pain and weakness

Tumor-induced osteomalacia is a rare and often misdiagnosed condition that presents with progressively worsening unexplained chronic pain and proximal muscle weakness. The osteomalacia leads to multiple stress fractures which do not heal properly, leading to progressive disability. It is caused by chronic hypophosphatemia due to inappropriate urinary phosphate wasting. This is due to a typically benign mesenchymal tumor that over-secretes a phospaturic hormone. Neurologists need to appreciate the relevance of chronic hypophosphatemia in people with chronic unexplained pain, as timely diagnosis and treatment of tumour-induced osteomalacia can be curative.

New treatments for rare bone diseases: hypophosphatemic rickets/osteomalacia

Phosphorus is one of the most abundant minerals in the human body; it is required to maintain bone integrity and mineralization, in addition to other biological processes. Phosphorus is regulated by parathyroid hormone, 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃], and fibroblast growth factor 23 (FGF-23) in a complex set of processes that occur in the gut, skeleton, and kidneys. Different molecular mechanisms - overproduction of FGF-23 by tumors responsible for oncogenic osteomalacia, generation of an FGF-23 mutant that is resistant to cleavage by enzymes, and impaired FGF-23 degradation due to a reduction in or loss of the PHEX gene - can lead to FGF-23-stimulating activity and the consequent waste of urinary phosphate and low levels of 1,25(OH)₂D₃. Conventional treatment consists of multiple daily doses of oral phosphate salts and vitamin D analogs, which may improve radiographic rickets but do not normalize growth. Complications of the conventional long-term treatment consist of hypercalcemia, hypercalciuria, nephrolithiasis, nephrocalcinosis, impaired renal function, and potentially chronic kidney disease. Recently, burosumab, an antibody against FGF-23, was approved as a novel therapy for children and adults with X-linked hypophosphatemia and patients with tumor-induced osteomalacia. Burosumab showed good performance in different trials in children and adults. It increased and sustained the serum phosphorus levels, decreased the rickets severity and pain scores, and improved mineralization. It offers a new perspective on the treatment of chronic and disabling diseases.

Tumour-induced osteomalacia due to residual benign glomangioma

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

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

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

Treating 'osteoporosis': a near miss in an unusual case of FGF-23-mediated hypophosphataemic osteomalacia

Summary

We present the case of a 60-year-old female who developed repeated atraumatic stress fractures. She was initially diagnosed with osteoporosis based on her dual-energy X-ray absorptiometry (DXA) scan bone mineral density (BMD) T-scores and started on denosumab therapy. Secondary osteoporosis screen revealed abnormal myeloma screen and low serum phosphate levels. It was thought that the patient had multiple myeloma with associated Fanconi-related tubular dysfunction. However, fibroblast growth factor-23 (FGF-23) levels were grossly elevated, making Fanconi syndrome unlikely. The patient was subsequently diagnosed with two separate conditions, namely cardiac amyloid light-chain (AL) amyloidosis and FGF-23-related hypophosphataemia, likely due to tumour-induced osteomalacia. This case highlights the importance of excluding osteomalacia as a cause of low BMD and checking FGF-23 levels in the workup for hypophosphataemia.

Learning Points

Tumour-induced osteomalacia is a difficult diagnosis as the tumour is often small and slow growing. Imaging may fail to identify a tumour, and treatment therefore consists of calcitriol and phosphate replacement. Tumour-induced osteomalacia should be suspected in the adult presenting with new-onset hypophosphataemia, elevated FGF-23 levels and isolated renal phosphate wasting. Serum phosphate is not part of the routine chemistry panels. Routinely checking phosphate levels prior to initiating antiresorptive therapy is warranted. DXA cannot distinguish low bone mineral density due to osteoporosis from osteomalacia. Antiresorptive therapy should be avoided in osteomalacia due to the risk of clinical and radiographic deterioration.

Tumor-Induced Osteomalacia: A Systematic Clinical Review of 895 Cases

Tumor-induced osteomalacia (TIO) is a rare and largely underdiagnosed paraneoplastic condition. Previous reviews often reported incomplete data on clinical aspects, diagnosis or prognosis. The aim of this study was to present a systematic clinical review of all published cases of TIO. A search was conducted in Pubmed, Embase, Web of Science from inception until April 23rd, 2020. We selected case reports and case series of patients diagnosed with TIO, with information on tumor localization and serum phosphate concentration. Two reviewers independently extracted data on biochemical and clinical characteristics including bone involvement, tumor localization and treatment. 468 articles with 895 unique TIO cases were included. Median age was 46 years (range 9 months-90 years) and 58.3% were males. Hypophosphatemia and inappropriately low or normal 1,25-dihydroxyvitamin D levels, characteristic for TIO, were present in 98% of cases. Median tumor size was 2.7 cm (range 0.5 to 25.0 cm). Serum fibroblast growth factor 23 was related to tumor size (r = 0.344, P < 0.001). In 32% of the cases the tumor was detected by physical examination. Data on bone phenotype confirmed skeletal involvement: 62% of cases with BMD data had a T-score of the lumbar spine ≤ - 2.5 (n = 61/99) and a fracture was reported in at least 39% of all cases (n = 346/895). Diagnostic delay was longer than 2 years in more than 80% of cases. 10% were reported to be malignant at histology. In conclusion, TIO is a debilitating disease characterized by a long diagnostic delay leading to metabolic disturbances and skeletal impairment. Increasing awareness of TIO should decrease its diagnostic delay and the clinical consequences.

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

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSION

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

Tumor-induced Osteomalacia: A Systematic Review and Individual Patient's Data Analysis

CONTEXT

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome, usually caused by small, benign, and slow-growing phosphaturic mesenchymal tumors. Clinically, TIO is characterized by renal phosphate leak, causing hypophosphatemia and osteomalacia. This review was performed to assess the clinical characteristics of TIO patients described worldwide so far.

EVIDENCE ACQUISITION

On June 26, 2021, a systematic search was performed in Medline, Google Scholar, Google book, and Cochrane Library using the terms: "tumor induced osteomalacia," "oncogenic osteomalacia," "hypophosphatemia." There were no language restrictions. This review was performed according to Preferred Reporting Items for Systematic reviews and Meta-Analyses criteria.

EVIDENCE RESULTS

Overall, 1725 TIO cases were collected. TIO was more frequent in adult men, who showed a higher incidence of fractures compared with TIO women. The TIO-causing neoplasms were identified in 1493 patients. The somatostatin receptor-based imaging modalities have the highest sensitivity for the identification of TIO-causing neoplasms. TIO-causing neoplasms were equally located in bone and soft tissues; the latter showed a higher prevalence of fractures and deformities. The surgery is the preferred TIO definitive treatment (successful in > 90% of patients). Promising nonsurgical therapies are treatments with burosumab in TIO patients with elevated fibroblast growth factor-23 levels, and with radiolabeled somatostatin analogs in patients with TIO-causing neoplasm identified by somatostatin receptor-based imaging techniques.

CONCLUSION

TIO occurs preferentially in adult men. The TIO clinical expressiveness is more severe in men as well as in patients with TIO-causing neoplasms located in soft tissues. Treatments with burosumab and with radiolabeled somatostatin analogs are the most promising nonsurgical therapies.

[FGF23 tumor induced osteomalacia]

Tumor induced osteomalacia is a rare acquired disease. The cause is a mesenchymal tumor secreting fibroblast growth factor 23 (FGF23). An excessive amount of FGF 23 disrupts the metabolism of phosphorus and vitamin D, which leads to severe paraneoplastic syndrome, manifested in the form of multiple fractures, severe pain in the bones and generalized myopathy. With oncogenic osteomalacia, a complete cure is possible with radical resection of the tumor. Unfortunately, localization, small size of formations and rare frequency of occurrence lead to the fact that the disease remains unrecognized for a long time and leads to severe, disabling consequences. A step-by-step approach to diagnosis improves treatment outcomes. First, a thorough anamnesis is collected, then functional visualization is performed and the diagnosis is confirmed by anatomical visualization of the tumor. After that, the method of choice is a surgical treatment. If resection is not possible, then conservative therapy with active metabolites of vitamin D and phosphorus salts is indicated. New therapeutic approaches, such as the antibody to FGF23 or the pan-inhibitor of receptors to FGF, are actively developing. This article provides an overview of modern approaches to the diagnosis and treatment of this disease.

Malignancy mimics- diagnostic perplexities for oral and maxillofacial pathologists

Objective

In pathology practice, one frequently encounters benign lesions which superficially resemble malignancy clinically and histopathologically. The diagnostic pitfalls can be avoided if the approach exemplified in the present study is followed. We expect that familiarity of these cases will be helpful for pathologists at the beginning of their career.

Methods

Clinical case records of all the pathological specimens reported in our laboratory from January 2018 to September 2019 were queried. Cases displaying pseudotumor features were reviewed along with the special stains were performed and immunohistochemistry (IHC) studies. A working classification of pseudotumors presenting in the oral cavity was proposed.

Results

Immunoglobulin G4-related disease, nodular fasciitis, fibrolipoma, odontogenic keratocyst with giant cell granuloma, juvenile ossifying fibroma with central giant cell granuloma and tumor-induced osteomalacia were the most common diagnoses where the tissue specimens resembled malignancies on routine clinicoradiological evaluation and light microscopy of tissue specimens. Their differential diagnosis and the pathological diagnostic dilemmas are explained. We have also highlighted the importance of correlating clinical, radiological and microscopic details with the findings deduced from advanced pathological aids to establish the final diagnosis.

Conclusions

Pathologists should be aware of the conditions where the diagnosis of malignancy needs stricter evaluation to rule out malignant mimics. In such scenarios, correlation of light microscopy findings with clinical and radiological details cannot be overemphasized. Advanced pathological aids such as IHC, where necessary are often indispensable for reaching the accurate diagnosis in these cases.

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.