Comparison of 18F-FDG and 68Ga DOTATATE PET/CT in localization of tumor causing oncogenic osteomalacia

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.

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

Key Clinical Message

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

Abstract

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

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.

Increased Uptake of Brown Tumor in 99m Tc-HYNIC-TOC Scintigraphy Mimicking Postoperative Recurrence of Tumor-Induced Osteomalacia

ABSTRACT

A 61-year-old man underwent a resection of tumor in the left tibia that caused osteomalacia 11 years ago. Postoperative bone pain and fatigue symptoms were briefly relieved but then recurred. To identify potential recurrent tumors, 99m Tc-HYNIC-TOC scintigraphy was performed. Images revealed an osteolytic lesion in the right tibia with increased uptake. The lesion was subsequently resected, which pathologically proved a brown tumor. Symptoms of bone pain and weakness caused by osteomalacia did not relieve 4 months after the operation. Here, we present a rare case of brown tumor with high activity on 99m Tc-HYNIC-TOC SPECT/CT, mimicking a culprit tumor of osteomalacia.

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.

Diagnostic accuracy of 99mTc-HYNIC-TOC SPECT/CT for detecting osteomalacia-associated tumors

OBJECTIVES

Tumor-induced osteomalacia (TIO) is a rare acquired paraneoplastic disorder characterized by hypophosphatemia resulting from tumor-secreted fibroblast growth factor-23 (FGF23). Surgical resection of the culprit TIO is the first choice of treatment. However, TIO is difficult to detect with conventional diagnostic tools due to its small size and variable location in the body. Somatostatin receptor scintigraphy (SSR) has recently emerged as a functional molecular imaging choice for TIO detection and localization. This research was undertaken to evaluate the efficacy of 99mTc-labeled hydrazinonicotinyl-Tyr3-octreotide (99mTc-HYNIC-TOC) SPECT/CT in detecting TIO.

METHODS

99mTc-HYNIC-TOC SPECT/CT and the available clinical data of 25 patients with suspected TIO were analyzed retrospectively. The 99mTc-HYNIC-TOC SPECT/CT findings were compared with the post-surgical pathology diagnosis and clinical follow-up results.

RESULTS

Using 99mTc-HYNIC-TOC SPECT/CT, suspicious tumors were found in 18 of the 25 patients, and 15 of them underwent surgical resection. The post-operative pathology confirmed a TIO in those 13 patients whose symptoms and biochemical anomalies gradually resolved after the surgery. The remaining five patients were finally considered false positives. Moreover, the 99mTc-HYNIC-TOC SPECT/CT results were negative in seven patients, with six patients being true negative (4 patients were diagnosed with acquired Fanconi syndrome and 2 patients responded well to conservative therapy) and one being false negative. Therefore, the sensitivity and specificity values of 99mTc-HYNIC-TOC SPECT/CT in the evaluation of TIO were 92.9% (13/14) and 54.5% (6/11), respectively. The overall accuracy of 99mTc-HYNIC-TOC SPECT/CT for detecting TIO was 76.0% (19/25).

CONCLUSIONS

The 99mTc-HYNIC-TOC SPECT/CT is an accurate imaging modality for locating culprit tumors in TIO.

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

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

Tumor induced osteomalacia from a peripheral mesenchymal tumour of the foot

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

Utility of Multimodality Approach Including Systemic FGF23 Venous Sampling in Localizing Phosphaturic Mesenchymal Tumors

Context

Tumor-induced osteomalacia (TIO) is one of the most common forms of acquired fibroblast growth factor 23 (FGF23)-related hypophosphatemia and is usually caused by phosphaturic mesenchymal tumors (PMTs). Although the complete resection of PMTs can cure TIO, preoperative localization of tumors by standard imaging modalities is often challenging. In addition to ¹⁸F-fluoro-2-deoxy-D-glucose positron emission tomography-computed tomography (FDG-PET) and ¹¹¹In-pentetreotide scintigraphy (SRS), systemic FGF23 venous sampling (FGF23VS) has been used to help localize PMTs in specialized institutions.

Objective

This study aimed to evaluate the diagnostic performance of each imaging test and their combinations in localizing PMTs.

Methods

In an observational retrospective study of patients with adult-onset FGF23-related osteomalacia who underwent all 3 imaging studies (FDG-PET, SRS, and FGF23VS), the rate of successful preoperative localization of the tumors was evaluated only in the patients with pathological diagnoses of PMTs, considering the possibility that pathogenesis of patients without identified tumors might be due to other causes such as late-onset hereditary FGF23-related hypophosphatemia.

Results

A total of 30 Japanese patients with TIO (median age, 60 years [range, 28-87 years]; 10 women [33.3%]) were included in the study. The success rate of preoperative localization for each test and combinations of 2 or 3 tests among 18 patients with PMTs was as follows: 72% (FDG-PET), 72% (SRS), 94% (FGF23VS), 89% (FDG-PET, SRS), 100% (FDG-PET, FGF23VS), 94% (SRS, FGF23VS), and 100% (FDG-PET, SRS, and FGF23VS).

Conclusion

We observed the highest localization rate of PMTs in patients with identified PMTs with the combination of FDG-PET and FGF23VS.

The Nose that Broke the Hip! Tumor Induced Osteomalacia Secondary to Phosphaturic Mesenchymal Nasal Tumor : A Case Report

Tumor induced osteomalacia is a rare paraneoplastic syndrome caused by usually small mesenchymal tumors. The tumors are commonly located in the extremities whereas occurrence in the nasal cavity is quite rare. An 18 year old male presented with asymmetric weakness of both lower limbs and difficulty in walking since one year. On evaluation he was found to have open femur head physes and iliac apophyses, low serum Phosphorus, low vitamin D, normal serum calcium, elevated PTH & alkaline phosphatase levels. FGF-23 levels in serum were elevated. DOTA NOC PET CT revealed tumor in the left nasal cavity abutting the nasal septum. Surgical excision of the tumor resulted in normalisation of the serum levels of phosphorus, vitamin D and FGF-23. This case report indicates the importance of maintaining high clinical suspicion and early detection of causative tumor using appropriate imaging techniques.

Tumor-induced osteomalacia characterized by "painful knee joint with difficulty in moving": a case report

BACKGROUND

Tumor-related osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by severe hypophosphatemia and osteomalacia. The diagnosis of TIO can be very difficult because of its nonspecific nature of clinical manifestations. Here we reported a case of young TIO patient with "painful knee joint with difficulty in moving" to improve the clinical diagnosis and treatment levels.

CASE PRESENTATION

The patient's clinical features were consistent with TIO. A tumor was successfully located in left tibial by ⁶⁸Ga-DOTATATE PET/CT, and then was surgically resected. Upon pathologic assessment, the tumor was diagnosed as phosphaturia stromal tumor (PMT) with positive Vim staining. After the surgery, serum phosphate level rapidly recovered and symptoms significantly improved.

CONCLUSION

TIO should be considered in patients with chronically hypophosphorus osteomalacia in the setting of no family history. Early removal of the responsible tumors is clinically essential for the treatment, and imaging examination is of great significance for tumor localization.

A Case Report of Hypophosphatemia Leading to the Diagnosis of Mesothelioma

Hypophosphatemia can be commonly encountered as an electrolyte imbalance and is defined as a value less than 0.8 mmol/l (2.5 mg/dl). It can be an incidental finding, but it is not uncommon to see it presenting with varied symptoms. It is good to have a clear diagnostic approach to this so adequate treatment can be instated.

We present a 66-year-old gentleman who presented with hypophosphatemia. Investigations confirmed renal phosphate wasting secondary to fibroblast growth factor-23 (FGF-23). Imaging showed right pleural effusion, and pleural biopsy confirmed malignant mesothelioma. This may just be an association rather than the cause of his hypophosphatemia. It does however highlight the importance of further investigations for patients with tumor-induced osteomalacia.

Head-to-Head Comparison of 68Ga-DOTA-TATE and 68Ga-DOTA-JR11 PET/CT in Patients With Tumor-Induced Osteomalacia: A Prospective Study

Background

The purpose of this study is to compare the sensitivity of ⁶⁸Ga-DOTA-JR11 and ⁶⁸Ga-DOTA-TATE PET/CT for detecting the responsible tumor of tumor-induced osteomalacia (TIO) and investigate if ⁶⁸Ga-DOTA-JR11 PET/CT can identify the culprit tumor of TIO in multiple suspicious lesions in ⁶⁸Ga-DOTA-TATE PET/CT.

Methods

A total of 19 patients with suspected TIO were prospectively recruited in this study. Each patient underwent whole-body PET/CT scan 40–60 min postinjection using ⁶⁸Ga-DOTA-TATE and ⁶⁸Ga-DOTA-JR11 on the same PET/CT, respectively in sequence, and on consecutive days. The diagnosis of TIO was confirmed by the combination of the postsurgical pathological results of the tumor and clinical information.

Results

Among the 19 patients with TIO who were included in this study, culprit tumors from all patients were confirmed pathologically. ⁶⁸Ga-DOTA-TATE PET/CT positively identified the causative tumor in 18/19 patients, whereas ⁶⁸Ga-DOTA-JR11 PET/CT was positive in 11/19 patients (94.7% vs. 57.9%, respectively; p < 0.05). ⁶⁸Ga-DOTA-TATE PET/CT demonstrated more than one increased focal activity in 7 patients for a total of 16 lesions (3 lesions each in 2 patients and 2 lesions each in the rest 5 patients). However, seven of these 16 lesions showed concordant results on ⁶⁸Ga-DOTA-JR11 PET/CT by demonstrating increased activity (one lesion in each of the 7 patients). The surgical specimens of the lesions in these 7 patients confirmed the phosphaturic mesenchymal tumor. A total of 11 culprit tumors were positive in both ⁶⁸Ga-DOTA-TATE and ⁶⁸Ga-DOTA-JR11 PET/CT. The SUVmax of 11 culprit tumors was significantly higher on ⁶⁸Ga-DOTA-TATE PET/CT compared with that on ⁶⁸Ga-DOTA-JR11 PET/CT (17.8 ± 12.5 vs. 6.8 ± 6.2; p < 0.05).

Conclusions

⁶⁸Ga-DOTA-TATE PET/CT is more sensitive to ⁶⁸Ga-DOTA-JR11 PET/CT in the detection of the culprit tumor of TIO. However, ⁶⁸Ga-DOTA-JR11 PET/CT might be helpful to identify the tumor in multiple suspicious lesions in ⁶⁸Ga-DOTA-TATE PET/CT.

Clinical Trial Registration

clinicaltrials.gov, identifier NCT 04689893.

Clinical Applications of Somatostatin Receptor (Agonist) PET Tracers beyond Neuroendocrine Tumors

Somatostatin receptor (SSTR) agonist tracers used in nuclear medicine scans are classically used for neuroendocrine tumor diagnosis and staging. SSTR are however, expressed more widely in a variety of cells as seen in the distribution of physiological tracer uptake during whole body scans. This provides opportunities for using these tracers for applications other than NETs and meningiomas. In this qualitative systematic review, novel diagnostics in SSTR-PET imaging are reviewed. A total of 70 studies comprised of 543 patients were qualitatively reviewed. Sarcoidosis, atherosclerosis and phosphaturic mesenchymal tumors represent the most studied applications currently with promising results. Other applications remain in progress where there are many case reports but a relative dearth of cohort studies. [¹⁸F]FDG PET provides the main comparative method in many cases but represents a well-established general PET technique that may be difficult to replace, without prospective clinical studies.

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.

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

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

Phosphaturic mesenchymal tumors: radiological aspects and suggested imaging pathway

Phosphaturic mesenchymal tumors (PMTs) are rare mesenchymal neoplasms of soft tissue or bone origin that can give rise to a challenge in diagnostic imaging. These tumors are frequently associated with tumor-induced osteomalacia, also called oncogenic osteomalacia, which is a rare paraneoplastic syndrome characterized by ectopic secretion of fibroblast growth factor 23, a hormone that regulates serum phosphate level. PMTs show polymorphic features on both radiological findings and histological examination, causing problems in diagnosis owing to their similarity with other mesenchymal tumors. Thus, this paper aims to describe radiological aspects of PMTs and suggest an imaging pathway for accurate diagnosis throughout the evidence from the literature review.

Oncogenic osteomalacia secondary to glomus tumor

SUMMARY

Oncogenic osteomalacia secondary to glomus tumor is extremely rare. Localization of causative tumors is critical as surgical resection can lead to a complete biochemical and clinical cure. We present a case of oncogenic osteomalacia treated with resection of glomus tumor. A 39-year-old woman with a history of chronic sinusitis presented with chronic body ache and muscle weakness. Biochemical evaluation revealed elevated alkaline phosphatase hypophosphatemia, increased urinary phosphate excretion, low calcitriol, and FGF23 was unsuppressed suggestive of oncogenic osteomalacia. Diagnostic studies showed increase uptake in multiple bones. Localization with MRI of paranasal sinuses revealed a sinonasal mass with concurrent uptake in the same area on the octreotide scan. Surgical resection of the sinonasal mass was consistent with the glomus tumor. The patient improved both clinically and biochemically postoperatively. Along with the case of oncogenic osteomalacia secondary to a glomus tumor, we have also discussed in detail the recent development in the diagnosis and management of oncogenic osteomalacia.

LEARNING POINTS

Tumor-induced osteomalacia is a rare cause of osteomalacia caused by the secretion of FGF23 from mesenchymal tumors. Mesenchymal tumors causing TIO are often difficult to localize and treat. Resection of the tumor can result in complete resolution of biochemical and clinical manifestations in a very short span of time. Glomus tumor can lead to tumor induced osteomalacia and should be surgically treated.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Comparison of 18 F-FDG PET/CT and 68 Ga-DOTATATE PET/CT in the Targeted Imaging of Culprit Tumors Causing Osteomalacia

Objective

To assess and compare the performance of fluorine‐18‐labeled fluorodeoxyglucose positron emission tomography (¹⁸F‐FDG‐PET/ CT) and gallium‐68‐labeled tetraazacyclododecanetetraacetic acid‐DPhe1‐Tyr3‐octreotate (⁶⁸Ga‐ DOTATATE) PET/CT in the targeted imaging of culprit tumors causing osteomalacia.

Methods

This was a clinical retrospective analysis. We analyzed 13 patients (five men, eight women; mean age, 49 years; range, 19–55 years) with suspicion of tumor‐induced osteomalacia (TIO) between March 2017 and October 2019. All patients underwent two functional imaging methods to locate the culprittumors. Studies were performed on a PET/CT scanner. The injection doses of ¹⁸F‐ FDG and ⁶⁸Ga‐DOTATATE were 0.5mCi/kg and approximately 5.0mCi, respectively. In the two scans, the whole body was captured from head to toe 45 to 60 min after intravenous tracer injection. ⁶⁸Ga‐DOTATATE PET/CT and ¹⁸F‐FDG PET/CT imaging results locate culprit tumors according to the following criteria: (i) abnormal foci uptake concentration was observed locally, and the uptake level was higher than the background level of the right lobe of the liver; (ii) combined CT showed or did not have obvious abnormal density changes; and (iii) non‐specific ingestion lesions due to fracture, arthritis, necrosis of femoral head are excluded. Compared with the results of pathological examination and clinical follow‐up, the sensitivity, specificity and accuracy of ⁶⁸Ga‐DOTATATE PET/CT imaging and ¹⁸F‐FDG PET/CT imaging for TIO were analyzed.

Results

All patients had symptoms of osteomalacia and hypophosphatemia. The lag time (symptoms to PET diagnosis) ranged from 2 to 12 years. There were eight cases of TIO patients and five cases of non‐TIO patients confirmed by surgery, pathology and follow‐up. Among the eight TIO patients, there were six cases (75.0%) of PMTs, one case (12.5%) of giant cell tumor, one case (12.5%) of hemangiopericutoma. Most (n = 6, 75.0%) of the confirmed tumors in our patient population were in the lower extremities, followed by craniofacial regions (n = 1, 12.5%), and torso (n = 1, 12.5%), respectively. Among the five non‐TIO patients, there were two cases of Fanconi syndrome, one case of rickets, and two cases of sporadic osteomalacia hypophosphorus. The culprit tumors could be located either in the bone (n = 5, 62.5%) or the soft tissue (n = 3, 37.5%). ¹⁸F‐FDG PET/CT was able to localize the tumor in six (6/13, 46.1%) patients. ⁶⁸Ga‐DOTATATE PET/CT detected tumor in 8 (83.3%) of 13 patients. The sensitivity of ⁶⁸Ga‐DOTATATE PET/CT imaging and ¹⁸F‐FDG PET/CT imaging in the evaluation of TIO in our patient population were 100% (8/8) vs 75% (6/8). The specificity of the two different methods was 80% (4/5). The overall accuracy was 92.3% (12/13) vs 76.9% (10/13).

Conclusions

⁶⁸Ga‐DOTATATE PET/CT is very effective in assessing hypophosphatemia patients with TIO typical symptoms compared with ¹⁸F‐FDG. Therefore, in clinically suspected cases of hypophosphatemic osteomalacia, ⁶⁸Ga‐DOTATATE PET/CT should be preferred as an imaging modality investigation to avoid delay in the treatment of this disease.

Prognostic Value of Positive Presurgical FDG PET/CT in the Evaluation of Tumor-Induced Osteomalacia

METHODS

Seventy-six patients who had surgically removed tumors that caused osteomalacia were included in this retrospective investigation. All patients underwent both 18F-FDG and 68Ga-DOTATATE PET/CT prior to surgery. The prognostic value of presurgical FDG PET/CT study was determined with 5-year follow-up.

RESULTS

In the presurgical evaluation, 68Ga-DOTATATE detected lesions in all 76 patients. However, FDG PET/CT was positive in only 25 among all 76 patients. Following surgical removal of the causative tumor, all 76 patients had symptomatic relief and normalization of the serum phosphate level initially. However, 15 of 76 cases (19.7%) had recurrent hypophosphatemia and became symptomatic again during the follow-up. Among these 15 patients with recurrence, 11 (73.3%) had recurrent lesions at the original location of the resected causative tumors, whereas 4 were in other locations due to malignant nature of the primary tumor. Interestingly, 14 of these 15 patients with recurrent disease had positive presurgical FDG PET/CT findings with an incident ratio of 56.0% (14 of 25). In contrast, only 1 patient with recurrent disease had negative presurgical FDG PET/CT scan with an incident ratio of 1.9% (1 of 51), significantly less than the positive presurgical FDG PET/CT group (P < 0.05).

CONCLUSIONS

A positive presurgical FDG PET/CT suggests increased likelihood for possible recurrence of TIO after surgical resection. In contrast, when a causative tumor detected by 68Ga-DOTATATE PET/CT does not have elevated activity on FDG PET/CT, the chance of recurrence is very small.

Diagnostic performance of 68Ga-DOTATOC PET/CT in tumor-induced osteomalacia

OBJECTIVE

Tumor-induced osteomalacia (TIO) is caused by typically small tumors that secrete fibroblast growth factor 23 (FGF23). As tumor resection is the only effective treatment for TIO, it is important to detect the culprit tumor. We aimed to assess the utility of 68Gallium-DOTA-D-Phe(1)-Tyr(3)-octreotide (68Ga-DOTATOC) PET/CT in TIO and the correlation between biochemical parameters and the PET/CT results.

METHODS

Thirty-five patients with clinically suspected TIO who had undergone 68Ga-DOTATOC PET/CT were retrospectively analyzed. 68Ga-DOTATOC PET/CT results were compared with biochemical parameters and the final diagnosis, including histopathology.

RESULTS

68Ga-DOTATOC PET/CT detected focal uptake consistent with TIO in 21/35 patients, one of which was considered false positive. In 16 patients, the cause of osteomalacia was confirmed histologically as phosphaturic mesenchymal tumor (n = 15) or fibrous dysplasia (n = 1). The other four patients were judged clinically as true positive by subsequent MRI and the clinical course. Overall, the detection rate of 68Ga-DOTATOC PET/CT was 57% (20/35). Median tumor maximum standardized uptake value (SUVmax) was 6.9 (range 1.5-37.7). There was no significant difference in serum intact FGF23 level between DOTATOC-positive and DOTATOC-negative cases, and no significant correlation was observed between intact FGF23 level and tumor SUVmax.

CONCLUSIONS

68Ga-DOTATOC PET/CT was clinically useful in detecting culprit tumors and subsequent patient management in TIO.

Usefulness of 68Ga-DOTATOC PET/CT to localize the culprit tumor inducing osteomalacia

Tumor-induced osteomalacia (TIO) is an uncommon paraneoplastic syndrome presenting with sustained hypophosphatemia. Treatment of choice is removal of the tumor causing the TIO, but identification of the culprit tumor by routine imaging is challenging. This study aimed to assess the usefulness of somatostatin receptor imaging, called ⁶⁸Ga-DOTATOC PET/CT, in the management of patients with TIO. Twelve patients who were suspected of having TIO underwent ⁶⁸Ga-DOTATOC PET/CT. Lesion detectability and maximum standardized uptake value (SUV_max) were determined and retrospectively compared with the clinical/imaging surveillance and histopathologic diagnosis. The median duration of suspected TIO with hypophosphatemia was 7.8 years (range 2.1–21.0). Conventional radiologic and/or nuclear medicine images failed to identify the culprit tumors. However, ⁶⁸Ga-DOTATOC PET/CT scans showed that 8 of the 12 patients had positive lesions, suggesting the presence of focal culprit tumors. The SUV_max of positive tumors was 1.9–45.7 (median: 11.5). Six skeletal lesions and two extra-skeletal lesions were identified. Seven of the lesions were pathologically confirmed as potential culprits of TIO. Hypophosphatemia was resolved in five patients who underwent lesion excision. The ⁶⁸Ga-DOTATOC PET/CT is a useful whole-body imaging modality for the detection of causative tumors in patients with suspected TIO.

Performance of 68Ga-DOTA-SST PET/CT, octreoscan SPECT/CT and 18F-FDG PET/CT in the detection of culprit tumors causing osteomalacia: a meta-analysis

Objectives

The objective of this study was to assess and compare the performance of ⁶⁸Ga-DOTA-conjugated-somatostatin-receptor-targeting-peptides (⁶⁸Ga-DOTA-SST) PET/CT, octreoscan-SPECT/CT and ¹⁸F-FDG-PET/CT in the detection of tumor-induced osteomalacia (TIO).

Methods

Relevant studies reporting the performance ⁶⁸Ga-DOTA-SST PET/CT, octreoscan-SPECT/CT and ¹⁸F-FDG-PET/CT in TIO were identified by searching PubMed, EMBASE, and Web of Science (last updated June 2019). Two authors independently extracted the numbers of true and false positives, and true and false negatives. The pooled estimates on a per-patient basis were calculated with 95% confidence interval (CI) obtained using a random-effects model.

Results

Fourteen studies comprising 346 patients were included in this meta-analysis. The meta-analysis provided the following results on a per-patient analysis. The pooled sensitivities of both ⁶⁸Ga-DOTA-SST PET/CT (90%, 95% CI 82–95%) and octreoscan-SPECT/CT (83%, 95% CI 75–89%) were found to be significantly higher (P < 0.005) than that of ¹⁸F-FDG PET/CT (67%, 95% CI 53–80%). There was no statistically significant difference between the sensitivity of ⁶⁸Ga-DOTA-SST PET/CT and octreoscan-SPECT/CT (P = 0.161). Owing to the low number of articles with true negative findings, the pooled specificities were not calculated. A total of 287 tumors were identified in 287 patients according to the data the included studies offered. The majority of the tumors were located in the lower extremities (59.6%, 171/287), followed by craniofacial regions (24.0%, 69/287), torso (9.4%%, 27/287), and upper extremities (6.9%, 20/287).

Conclusion

This meta-analysis demonstrates that somatostatin receptor-based imaging modalities outperformed ¹⁸F-FDG PET/CT in the detection of TIO, with ⁶⁸Ga-DOTA-SST PET/CT performing slightly better than octreoscan-SPECT/CT.

Prolonged Hypophosphatemia and Intensive Care After Curative Surgery of Tumor Induced Osteomalacia: A Case Report

INTRODUCTION

Rare FGF23-producing mesenchymal tumors lead to paraneoplastic tumor-induced osteomalacia (TIO) presenting with phosphate wasting, hypophosphatemia, chronic hypomineralization of the bone, fragility fractures and muscle weakness. Diagnosis of TIO requires exclusion of other etiologies and careful search for a mesenchymal tumor that often is very small and can appear anywhere in the body. Surgical removal of the tumor is the only definitive treatment of TIO. Surgical complications due to chronic hypophosphatemia are not well recognized.

CASE DESCRIPTION

The current case describes severe fragility fractures in a 58-year-old woman, who lost her ability to walk and was bedridden for two years. First, the initial diagnostic laboratory work-up did not include serum phosphorus measurements, second, the suspicion of adverse effects of pioglitazone as an underlying cause delayed correct diagnosis for at least two years. After biochemical discovery of hyperphosphaturic hypophosphatemia at a tertiary referral centre, a FGF23-producing tumor of the mandible was discovered on physical examination, and then surgically removed. Postoperatively, severe hypophosphatemia and muscle weakness prolonged the need for ventilation support, intensive care and phosphate supplementation. After two years of rehabilitation, the patient was able to walk short distances. The tumor has not recurred, and serum phosphate concentration has remained within normal limits during 3.5 years of follow-up.

CONCLUSIONS

The case report illustrates knowledge gaps in the diagnostic work-up of rare causes of low bone mass and fragility fractures. Compared to other low phosphate conditions, surgical recovery from TIO-induced hypophosphatemia warrants special attention. Increased alkaline phosphatase concentration may indicate impaired postsurgical recovery due to prolonged hypophosphatemia, underlining the need for proactive perioperative correction of hypophosphatemia.

Diagnostic efficiency of 68Ga-DOTANOC PET/CT in patients with suspected tumour-induced osteomalacia

OBJECTIVES

Currently, the main challenge in tumour-induced osteomalacia (TIO) is the difficulty in locating culprit tumours for definitive diagnosis and surgical therapy. Herein, we retrospectively evaluate the efficiency of ⁶⁸Ga-DOTANOC PET/CT in the localisation and diagnosis of TIO, and compared with ¹⁸F-FDG.

METHODS

Twenty-four consecutive patients with hypophosphataemic osteomalacia (HO) and suspicion of TIO who were referred to our centre for ⁶⁸Ga-DOTANOC PET/CT scanning were retrospectively reviewed. The images were evaluated qualitatively as well as semi-quantitatively, and imaging results were compared with the final diagnoses.

RESULTS

Among the total of 21 patients who were included in the final analyses, 17 were diagnosed with TIO, while four were proven to have other causes of HO. ⁶⁸Ga-DOTANOC PET/CT produced positive results in 16 of the 17 patients with TIO, representing a sensitivity of 94.1%. Moreover, the ⁶⁸Ga-DOTANOC PET/CT results were negative in 3 of the 4 patients without TIO, representing a specificity of 75.0%. The overall accuracy of ⁶⁸Ga-DOTANOC PET/CT in locating the tumours responsible for TIO is 90.5%. In particular, ⁶⁸Ga-DOTANOC PET/CT detected the culprit tumours in 4 out of 10 patients with negative results on previous ¹⁸F-FDG PET/CT and showed a significantly higher T/M ratio of tumours than ¹⁸F-FDG PET/CT in the same patients (n = 10; 4.76 ± 3.08 vs 1.95 ± 1.33, p < 0.05).

CONCLUSIONS

⁶⁸Ga-DOTANOC PET/CT is an accurate imaging modality in the localisation of tumours for TIO. It is superior to ¹⁸F-FDG PET/CT and may be useful in the differential diagnosis of HO.

KEY POINTS

• TIO should be considered a possible cause for patients diagnosed with HO, which usually needs to be differentiated from other aetiologies. • ⁶⁸Ga-DOTANOC PET/CT is an accurate imaging modality in locating culprit tumours for TIO, superior to ¹⁸F-FDG PET/CT.

FGF23-related hypophosphatemia in patients with low bone mineral density and fragility fractures: challenges in diagnosis and management

PURPOSE

Hypophosphatemia (HP) can be observed in patients evaluated for skeletal fragility. We investigated prevalence of HP among outpatients referred for low bone density or fragility fractures, HP-associated clinical and biochemical features and outcomes of recommended diagnostic algorithm in our cohort.

METHODS

Chronic HP (phosphate ≤ 2.7 mg/dL over 6 months or longer) was retrospectively investigated among 2319 patients. In renal wasting-related HP, intact FGF23 was assessed; non-suppressed FGF23 prompted the performance of ⁶⁸Ga-DOTATOC PET/CT in the suspicion of tumor-induced steomalacia (TIO).

RESULTS

Renal wasting-related HP (median 2.2, range 1.6-2.6 mg/dL) was observed in 19 patients (0.82%). FGF23 levels were suppressed in two patients diagnosed with renal tubular disease, increased in one and within normal range in most patients. X-linked hypophosphatemic rickets was diagnosed in one woman. In the remaining 16 patients, highly prevalent fragility fractures (50%) and severely reduced bone mineral density were detected, though diagnostic criteria for osteomalacia were not fulfilled. ⁶⁸Ga-PET was performed in nine patients and was positive in four. While intact FGF23 levels alone failed to differentiate PET's outcomes (positive: FGF23 median 70.5 pg/mL; negative: 52 pg/mL, P = 0.462), the coexistence of multiple biochemical and radiologic alterations performed better in prediction of PET's positivity.

CONCLUSION

Mild, apparently unexplained HP is observed in 0.82% of patients with low bone density or fragility fractures. In asymptomatic patients with isolated mild hypophosphatemia, the probability of finding an underlying tumor disease is very low, and utility of extensive and expensive diagnostic workup should be carefully considered in this setting.

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

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

Surgical Treatment and Outcomes for Sinonasal and Skull Base Phosphaturic Mesenchymal Tumors

OBJECTIVE

To describe our clinical experience with surgical treatments for sinonasal phosphaturic mesenchymal tumors diagnosed at our institution.

STUDY DESIGN

Retrospective case series.

SETTING

Affiliated Sixth People's Hospital, Shanghai Jiao Tong University.

SUBJECTS AND METHODS

We retrospectively reviewed the medical records of 10 patients diagnosed with phosphaturic mesenchymal tumors associated with tumor-induced osteomalacia between December 2014 and October 2019.

RESULTS

There were 4 men and 6 women with a disease course of 1 to 19 years. All patients exhibited hypophosphatemia and tumor-induced osteomalacia. The tumor was located in the sinonasal region, frontal bone, and temporal bone in 8 patients, 1 patient, and 1 patient, respectively. Technetium-99m octreotide scintigraphy was used for tumor localization in 4 cases. Six patients underwent endoscopic resection; the remaining 4 underwent unilateral transorbital anterior and posterior ethmoid artery ligation + endoscopic resection, endoscopic resection + skull base repair, internal carotid artery stenting + transcatheter arterial embolization + temporal bone tumor excision + adipose tissue plugging, and endoscopic resection + transfrontal craniotomy (n = 1 each). Two patients had a history of incomplete endoscopic resection. All patients achieved clinical remission and normalized biochemical indices after surgery. Only 1 patient developed recurrence and died of a brain hernia.

CONCLUSIONS

A diagnosis of sinonasal phosphaturic mesenchymal tumors should be based on a combination of clinical, imaging, and pathological findings. Technetium-99m octreotide scintigraphy helps in locating the tumor. Complete surgical excision guarantees clinical remission, and preoperative transcatheter arterial embolization or feeding artery ligation may reduce intraoperative bleeding in cases of highly vascularized tumors.

Approach to patients with hypophosphataemia

Phosphate metabolism is an evolving area of basic and clinical research. In the past 15 years, knowledge on disturbances of phosphate homoeostasis has expanded, as has the discovery of new targeted therapies. Hypophosphataemia might be the biochemical finding in several diseases, and its clinical evaluation should initially focus on the assessment of pathophysiological mechanisms leading to low serum phosphate concentrations. Clinical consequences of hypophosphataemia can involve multiple organ systems and vary depending on several factors, the most important being the underlying disorder. This Review focuses on the approach to patients with hypophosphataemia and how underlying pathophysiological mechanisms should be understood in the evaluation of differential diagnosis. We define an algorithm for the assessment of hypophosphataemia and review the most up-to-date literature on specific therapies. Continuous research in this area will result in a better understanding and management of patients with hypophosphataemia.

Intramastoid Phosphaturic Mesenchymal Tumor Causing Hypophosphatemic Osteomalacia Detected on 68Ga-DOTATATE PET/CT But Not on 99mTc-Sestamibi and 18F-FDG Scans

⁶⁸Ga-DOTATATE uptake in mesenchymal tumors causing hypophosphatemic osteomalacia has been recently described. Herein, we present a case of ⁶⁸Ga-DOTATATE uptake in an intramastoid phosphaturic mesenchymal tumor that had not been depicted in previous ^99mTc-Sestamibi and ¹⁸F-FDG scans. The lesion was surgically removed and the phosphorus level increased to the normal range.

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

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

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.

When Low Bone Mineral Density and Fractures Is Not Osteoporosis

PURPOSE OF REVIEW

To review the differential diagnosis of low bone mineral density (BMD).

RECENT FINDINGS

Osteoporosis is the most common cause of low BMD in adults; however, non-osteoporotic causes of low BMD should be considered in the differential diagnosis of patients with low BMD. Mild osteogenesis imperfecta, osteomalacia, and mineral and bone disorder of chronic kidney disease as well as several other rare diseases can be characterized by low BMD. This review summarizes the differential diagnosis of low BMD. It is important to differentiate osteoporosis from other causes of low BMD since treatment regimens can vary tremendously between these different disease processes. In fact, some treatments for osteoporosis could worsen or exacerbate the mineral abnormalities in other causes of low BMD.

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

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

Imaging features of phosphaturic mesenchymal tumors

OBJECTIVE

To examine the CT and MR imaging features of phosphaturic mesenchymal tumors (PMTs).

MATERIALS AND METHODS

With IRB approval, our institutional radiology/pathology database was reviewed for pathologically-proven PMTs. CT and MRI examinations were reviewed in consensus noting several imaging features, and if available, comparative molecular imaging tests were analyzed.

RESULTS

We identified 39 patients (21 male, 18 females) with 40 PMTs [mean age, 52.9 ± 14.9 years (range, 14-78)], including 20 bone and 20 soft tissue lesions. Mean maximal lesion diameter was 3.4 ± 2.0 cm (range, 1.1-9.8). 12/18 primary bone lesions (66.6%) were osteolytic and 15/20 (75.0%) had a narrow zone of transition. Internal matrix was present in 18/32 (56.3%) lesions. PMTs were most commonly T1 isointense (31/37, 83.8%), T2 hyperintense (14/36, 38.9%), and solidly enhancing (21/30, 70.0%). The majority (32/36, 88.9%) contained areas of dark T2 signal. 8/9 PMTs were positive by ^99mTc-sestamibi scintigraphy, 2/4 by ¹¹¹In-pentetreotide scintigraphy, 2/2 by ⁶⁸Ga-DOTATATE PET/CT and 11/13 by ¹⁸F-FDG PET/CT. On FDG PET/CT, the mean SUVmax was 4.1 ± 2.5 (range, 1.5-10.8).

CONCLUSIONS

Osseous PMTs are commonly osteolytic with a narrow zone of transition. Both bone and soft tissue PMTs often contain matrix and areas of dark T2 signal on MRI, independent of the presence of matrix. However, PMTs may mimic other bone and soft tissue neoplasms, including fibrous dysplasia, tenosynovial giant cell tumor, and even atypical lipomatous tumor. As such, clinical presentation and laboratory correlation are critical to PMT recognition and accurate diagnosis.

ACR Practice Parameter for the Performance of Gallium-68 DOTATATE PET/CT for Neuroendocrine Tumors

Radiopharmaceuticals targeting cell surface expression of somatostatin receptors (SSTRs) are particularly useful in the evaluation of neuroendocrine tumors. Gallium-68 DOTA-Tyr-octreotatate (Ga-DOTATATE) primarily binds to SSTR type 2 receptors. Ga DOTATATE PET/CT is proven to have high impact on the management of neuroendocrine patients compared to traditional anatomical imaging as well as provides additional information over that of conventional nuclear medicine studies (indium-III DTPA-octreotide). It can result in change in management of approximately 75% of patients with neuroendocrine tumors. Ga DOTATATE and F FDG PET/CT imaging are complementary, with the degree of uptake varying depending on the degree of differentiation of the tumor. Well-differentiated tumors maintain their SSTRs and are positive on Ga DOTATATE PET/CT scan, while dedifferentiated tumors are less likely to demonstrate uptake of Ga DOTATATE but will demonstrate uptake with F FDG PET/CT. In addition, Ga DOTATATE PET/CT identifies patients with SSTR expression in their tumors, who have progressed on somatostatin analog therapy, for treatment with Lu DOTATATE.

ACR-ACNM Practice Parameter for the Performance of Fluorine-18 Fluciclovine-PET/CT for Recurrent Prostate Cancer

The American College of Radiology (ACR) and American College of Nuclear Medicine (ACNM) collaborated to develop a clinical practice document for the performance of fluciclovine positron-emission tomography (PET) / computed tomography (CT) in the evaluation of patients with suspected prostate cancer recurrence based on the elevation of prostate-specific antigen (PSA) level (biochemical recurrence) after prior therapy. Prostate cancer is the third leading cause of cancer death in the United States. Up to 50% of patients diagnosed with prostate cancer will develop biochemical failure after initial therapy. The differentiation of local from extraprostatic recurrence plays a critical role in patient management. The use of functional imaging targeting features of cancer metabolism has proven highly useful in this regard. Amino acid transport is upregulated in prostate cancer. Fluciclovine (anti-1-amino-3-F-18-fluorocyclobutane-1-carboxylic acid, FACBC, Axumin™) is an artificial amino acid PET tracer which demonstrates utility in the diagnosis of recurrent prostate cancer with significant added value to conventional imaging.

Sinonasal hemangiopericytoma caused hypophosphatemic osteomalacia: A case report

RATIONALE

Tumor-induced osteomalacia (TIO) is a rare, paraneoplastic syndrome featured with fibroblast growth factor 23 (FGF23) secretion primarily by benign mesenchymal tumors and sometimes by malignancies. TIO diagnosis and treatment is often delayed because TIO usually has nonspecific generalized bone pain and weakness, and location of TIO tumor is quite challenging. Very few TIO caused by sinonasal hemangiopericytoma have been reported in the literature.

PATIENT CONCERNS

A 40-year-old Chinese woman presented with diffuse bone pain for more than 1 year. Laboratory examination showed hypophosphatemia, hyperphosphaturia, hypocalcemia, an elevated serum alkaline phosphatase (ALP) level and bone-specific ALP level. Imaging studies revealed low bone mineral density (BMD) and multiple pseudofractures at the ribs. F-18 fluorodeoxyglucose positron emission tomography was negative in searching for tumors. Because no tumor was located, the patient was treated with oral phosphate, calcium, and alfacalcidol, and achieved great relief in her symptoms and improvement in BMD. Six years later, the patient had breast cancer surgery and received chemotherapy, and still had hypophosphatemia. During this time, nasopharyngo-fiberscope showed nasal mass in her left nasal cavity. Then she had her nasal polyps removed and surprisingly the serum phosphate became normal.

DIAGNOSES AND INTERVENTIONS

The patient had the nasal mass resected, and pathological diagnosis of the nasal mass was sinonasal hemangiopericytoma. Immunohistochemical analysis was positive for FGF23. Thus the final diagnosis was osteomalacia induced by sinonasal hemangiopericytoma. Phosphate supplementation and alfacalcidol were discontinued.

OUTCOMES

The patient had normal serum phosphate after 6-month follow-up.

LESSONS

By presenting this case, we hope to remind clinicians that in patients with osteomalacia with undetermined reason and intranasal polypoid mass, sinonasal hemangiopericytoma should be suspected.

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.

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

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

Yield of diagnostic tests in unexplained renal hypophosphatemia: a case series

BACKGROUND

Isolated renal hypophosphatemia may be inherited or acquired. An increasing number of patients with unexplained renal hypophosphatemia is being referred to our clinics, but the optimal diagnostic work-up is not known. Therefore, the aim of this study was to assess the diagnostic yield in these patients.

METHODS

We retrospectively evaluated all patients who were referred because of unexplained isolated renal hypophosphatemia to two academic tertiary referral centers in The Netherlands in the period of 2013-2017.

RESULTS

We evaluated 17 patients. In five female patients renal hypophosphatemia could be attributed to the use of oral contraceptives. The other 12 patients had a median age of 48 years (10 males). There were no other signs of tubulopathy and none of the patients used drugs known to be associated with hypophosphatemia. FGF23 levels were above normal (> 125 RU/ml) in 2/12 patients. Genetic testing, performed in all patients, did not identify a mutation in genes known to be associated with renal phosphate wasting. A scan with a radiolabeled somatostatin analogue was performed in 8 patients. In one patient, with an FGF23 level of 110 RU/ml, an increased uptake of the somatostatin analog was observed due to tumor induced osteomalacia (TIO).

CONCLUSIONS

Oral contraceptive use is an important but under-recognized cause of renal hypophosphatemia. The cause of isolated renal hypophosphatemia remained unexplained in the majority of other patients despite extensive and expensive additional investigations. The pre-test probability for tumor-induced osteomalacia or inherited renal hypophosphatemia in a patient with aspecific complaints and a normal FGF23 level is low. Further research is needed to investigate which patients should be screened for TIO. At present we suggest to perform somatostatin scans only in patients with severe complaints, elevated FGF23 levels, or progressive disease.