99mTc-HYNIC-TOC in the Evaluation of Recurrent Tumor-Induced Osteomalacia

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.

Lung Nodule as Culprit Lesion Causing Recurrent Tumor-Induced Osteomalacia Revealed by 68Ga-DOTATATE PET/CT

ABSTRACT

Neoplasms that cause tumor-induced osteomalacia are very rarely located in the lung. A 27-year-old man underwent a surgery in the right femoral head to remove the tumor that induced osteomalacia 8 years ago with complete symptomatic relief. However, his bone pain occurred again recently, which lead to suspicion of a recurrent tumor-induced osteomalacia. 68Ga-DOTATATE PET/CT images showed a pulmonary nodule with mildly increased uptake along with increased activity in the left foot. The pulmonary nodule was subsequently resected and was pathologically confirmed as a phosphaturic mesenchymal tumor. The symptoms were completely relieved postsurgery.

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.

Breast Carcinoma Shown on 99mTc-HYNIC-TOC Study Performed to Evaluate Tumor-Induced Osteomalacia

ABSTRACT

A 74-year-old woman with a history of suspected tumor-induced osteomalacia underwent 99mTc-HYNIC-TOC scintigraphy to search potential culprit tumor. The images showed one in the middle shaft of left femur without corresponding morphology change on the CT portion of the subsequent SPECT/CT images. The patient declined surgical exploration of the left femur. Another activity was in the right breast, which was resected and pathologically confirmed as breast carcinoma. Postsurgically, the patient's symptoms were not improved. Four years later, a repeat 99mTc-HYNIC-TOC scintigraphy showed more prominent activity in the left femur with gross abnormality on the corresponding CT images.

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.

Adrenal Castleman Disease on 99mTc-HYNIC-TOC Scan and FDG PET/CT

Adrenal Castleman disease is very rare. We reported image findings of a right adrenal mass in a 75-year-old man on Tc-HYNIC-TOC scan and FDG PET/CT. There was obviously elevated Tc-HYNIC-TOC activity, but the intensity of FDG activity was remarkable. Pheochromocytoma was initially suspected. However, pathology from resected specimen showed adrenal Castleman disease.

Potential Utilization of Lymphoscintigraphy in Patients With Klippel-Trenaunay Syndrome

PURPOSE

Klippel-Trenaunay syndrome (KTS) is a rare disease that was characterized by vascular malformation. Lymphatic malformation was also commonly associated with KTS. However, the application of lymphoscintigraphy in the management of patients with KTS was rarely described. The purpose of this study is to assess whether the findings of lymphoscintigraphy can aid the management of the patients with KTS.

METHODS

A total of 28 patients with known KTS who underwent Tc-dextran lymphoscintigraphy with lower extremity tracer injection were included in this retrospective analysis. The images from lymphoscintigraphy were reviewed for any abnormalities in the body with the attention on the region of left subclavian-jugular venous angle.

RESULTS

In addition to abnormal activity in the other regions, abnormal activity in the left subclavian-jugular venous angle was visualized in over half of the patients (53.6%, 15/28). Based on the findings of the lymphoscintigraphy, 7 patients with left subclavian-jugular venous angle activity underwent thoracic duct decompression. In 4 patients with postsurgery follow-up, 3 achieved significant, measurable symptomatic relief.

CONCLUSIONS

Lymphoscintigraphy can be used to assess potential candidates for thoracic duct decompression to alleviate the symptoms in patients with KTS.

99mTc-Labeled Native RBC Scintigraphy in Distinguishing Polysplenia From Abdominal Masses in a Patient With Situs Inversus Totalis

A 39-year-old previously healthy woman presented possible hematuria. An ultrasound examination showed right adrenal mass and suggested pheochromocytoma. A Tc-HYNIC-TOC SPECT/CT was performed, which incidentally detected situs inversus totalis and suspicion of polysplenia without definite normal spleen in the right upper abdomen. In order to differentiate the polysplenia from other etiologies, a heat-damaged Tc RBC scintigraphy was performed. The images showed significant activity in the multiple soft tissue nodules in the posterior right abdomen, consistent with ectopic polysplenia.