Tumor-induced Osteomalacia Caused by a Parotid Tumor

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.

Parotid incidentalomas: a systematic review

OBJECTIVE

Parotid incidentalomas on fluorodeoxyglucose positron emission tomography/computed tomography imaging are rare. A systematic review was performed to assess their aetiology and association with scanning indication, and to develop an evidence-based algorithm for their management.

METHODS

A literature search was performed on 25 August 2020 using the keywords 'incidentaloma', 'incidental finding', 'parotid', 'parotid gland', 'salivary gland' and 'head and neck'. Articles were reviewed by two authors before their inclusion.

RESULTS

Forty articles were included, totalling 558 incidentalomas. The mean incidence was 0.74 per cent. Lung cancer was the most common imaging indication. The most common aetiologies were cystadenolymphoma, pleomorphic salivary adenoma and metastases. Only cystadenolymphoma (p = 0.015) and pleomorphic salivary adenoma (p = 0.011) were significantly associated with a primary malignancy (lung). The most common further investigations were aspiration cytology, ultrasound imaging and core biopsy, usually prior to parotidectomy.

CONCLUSION

If appropriate, parotid incidentalomas should be followed up with flexible endoscopy, skin examinations, and head and neck examinations. Ultrasound-guided core biopsy provides higher accuracy, avoiding repeat sampling and excision biopsy.

Left maxillary sinus tumour-induced hypophosphataemic osteomalacia and combined with thyroid papillary carcinoma: a case report and literature review

Tumour-induced osteomalacia (TIO) is a rare disease characterised by hypophosphataemia and clinical symptoms of osteomalacia. Herein we report the case of a 29-year-old man who was admitted to hospital with progressive bone pain and was diagnosed with TIO caused by maxillary sinus tumours. In the preoperative evaluation, it was found that the patient had thyroid malignant tumours at the same time. Two operations were performed separately on the left maxillary sinus tumour and thyroid tumour after complete examination. After tumour resections, the symptoms of bone pain were relieved and the level of blood phosphorus was restored, long-term replacement therapy was needed for thyroid. When a patient is diagnosed with TIO, it is necessary to screen for the presence of other malignant tumours and explore the treatment options in order to benefit patients preferably.

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.

Ectopic expression of Klotho in fibroblast growth factor 23 (FGF23)-producing tumors that cause tumor-induced rickets/osteomalacia (TIO)

Tumor-induced rickets/osteomalacia (TIO) is a rare paraneoplastic syndrome caused by tumors that ectopically express fibroblast growth factor 23 (FGF23). FGF23 is a bone-derived hormone that regulates serum phosphate concentrations. Patients with TIO develop hypophosphatemic rickets/osteomalacia due to FGF23 excess and suffer from symptoms such as leg deformities, bone pain, skeletal muscle myopathy, and multiple fractures/pseudofractures. Usually, successful surgical removal of the causative tumors normalizes serum FGF23 and phosphate concentrations in patients with TIO. Most FGF23-producing tumors associated with TIO are histologically called phosphaturic mesenchymal tumor, mixed connective tissue variant (PMTMCT). The precise mechanism by which these tumors ectopically overproduce FGF23 outside of bone is yet to be clarified. Therefore, we performed an RNA sequencing analysis of a PMTMCT that was found in the left parotid gland of a patient with TIO. Among the upregulated genes, we focused on Klotho, the protein product of which is a single pass transmembrane protein that works along with an FGF receptor 1c as a receptor complex for FGF23. Subsequent histological analysis confirmed the ectopic expression of Klotho in other PMTMCTs. From these results, we assume that the ectopic expression of Klotho in PTMMCTs enables a positive feedback loop in FGF23 production via the activation of FGF receptor 1c and exacerbates disease manifestations in TIO.

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Klotho is ectopically expressed in the FGF23-producing mesenchymal tumors.

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Klotho enables the activation of the FGFR signaling pathway in PMTMCTs.

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Klotho enables the autocrine/paracrine effects of FGF23 in PMTMCTs.