Neurofibromatosis type 1 associated with hypophosphatemic osteomalacia due to hypersecretion of fibroblast growth factor 23: a case report

Tumor-induced Osteomalacia: A Case Report and Etiological Analysis with Literature Review

BACKGROUND

Tumor-induced osteomalacia (TIO) belongs to a rare disease of the paraneoplastic syndrome. Phosphate uric mesenchymal tumor (PMT) is the most common cause of TIO, while the possibility of other tumors cannot be excluded.

CASE PRESENTATION

We present a case of a 36-year-old female patient with systemic skeletal abnormalities. The woman complained of low back pain with mild motor dysfunction for 2 years. Laboratory examination showed abnormalities in markers of bone metabolism, parathyroid hormone (PTH), vitamin D and serum phosphorus. Pooled imaging examination indicated extension abnormalities in the skeletal system and a single lesion in the right femoral head. The lesion of the right femoral was imaging with somatostatin receptor-positive, which was highly suggestive of a single neuroendocrine tumor. CT guided right femoral tumorectomy and bone grafting were performed when medical treatment failed. Postoperative pathological diagnosis was phosphate urinary mesenchymal tumor secreting fibroblast growth factor 23 (FGF23), which accorded with pre-operative expectations. The postoperative symptoms were effectively relieved, and indicators returned to normal.

CONCLUSION

The tumors causing TIO exhibited significant heterogeneity in terms of tissue origin, pathological characteristics and biological behavior, but the unique common characteristic is the secretion of FGF23. With significant progress in diagnosis and treatment, the clinical follow-up of most TIO patients shows a good prognosis, but the prognosis of those with malignant tumors is relatively poor.

Clinical Challenges in Diagnosis, Tumor Localization and Treatment of Tumor-Induced Osteomalacia: Outcome of a Retrospective Surveillance

Tumor-induced osteomalacia (TIO) is an acquired fibroblast growth factor 23 (FGF23)-related hypophosphatemic osteomalacia caused by phosphaturic mesenchymal tumors (PMTs) developed in the bone or soft tissue. Diagnostic delay should be addressed, and ideal techniques to localize PMTs and efficient treatment options should be explored to improve the outcomes of this rare disease. To clarify the detailed clinical course and outcomes of TIO patients, retrospective questionnaire surveys were conducted among physicians from the Japanese Society for Bone and Mineral Research (JSBMR) and the Japan Endocrine Society (JES). The primary survey collected the number of TIO patients between January 2007 and December 2018. The secondary survey aimed to obtain the detailed characteristics, laboratory data, and outcomes. Eighty-eight patients (52 males, mean: 52 years old) were included, and 24 patients were clinically diagnosed with TIO without localized PMTs. The median duration from the onset to detection of high FGF23 levels was 3.4 years, with 77 patients being initially misdiagnosed. Among the methods used to detect small, localized PMTs (≤10 mm), fluorine-18-fluorodeoxyglucose-positron emission tomography/computed tomography and somatostatin receptor scintigraphy were less sensitive than somatostatin receptor positron emission tomography/computed tomography (SRPET/CT). Systemic venous sampling (SVS) of FGF23 was performed in 53 patients; among them, SVS was considered useful for detecting localized PMTs in 45 patients with diverse tumor sizes. Finally, 45 patients achieved biochemical remission by surgery, 39 patients continued pharmaceutical treatment, including burosumab (11 patients), and four patients died. These results encouraged us to further increase the awareness of TIO and to improve the accessibility of SRPET/CT and SVS. Further evidence about the efficacy of new pharmaceutical treatments is awaited. © 2022 American Society for Bone and Mineral Research (ASBMR).

Diagnosis and surgical treatment of tumor-induced osteomalacia—a literature review and a case report

Background

Tumor-induced osteomalacia (TIO) is a rare condition with fewer than 500 cases reported in the literature although described. Phosphaturic mesenchymal tumor (PMT) is often unrecognized cause of hypophosphatemia. This case report aims to highlight such a rare association which warrants clinical and radiologist attention.

Case

A 51-year-old man had pain in his feet 2 years prior to the most recent presentation in our clinic. The patient experienced increasingly severe body aches and pain, which affected the feet, hips, knees, ribs, waist, and shoulders. MRI and CT led to the diagnosis of multiple insufficiency fractures. Laboratory tests showed that inorganic phosphate (IP) levels had decreased to 0.52 mmol/L(0.81–1.45 mmol/L), while alkaline phosphatase (ALP) had increased to 216 U/L(38.0–126.0 U/L). Positron emission tomography computed tomography showed tumor-derived hypophosphate osteomalacia of the right iliac wing; surgical resection was performed. markers of bone metabolism and bone density returned normal postoperative, after 9 months follow-up.

Conclusion

The possibility of tumor-induced osteomalacia should be considered if unexplained joint pain, decreased bone mineral density, increased ALP and insufficiency fractures, and no similar family history are found in adult patients. Surgical resection of the tumor is the key to the treatment.