Category: Calcium/Bone Disorders

Monitor: 1

1 - TUMOR INDUCED OSTEOMALACIA: A CHALLENGING DIAGNOSIS

Thursday, Apr 25
1:00 PM – 1:30 PM

Objective :

Tumor induced Osteomalacia (TIO) is a rare acquired form of hypophosphatemic osteomalacia. It is caused by a mesenchymal tumor that produces fibroblast growth factor 23 (FGF-23), a hormone which decreases tubular phosphate reabsorption and impairs renal hydroxylation of 25 hydroxy vitamin D. This leads to renal phosphate wasting and hypophosphatemic osteomalacia. Clinical presentation is characterized by fatigue, myalgia, bone pain and stress fractures. Although resection of the underlying tumor leads to cure, localization of the tumor can be challenging. We describe such a case.


Methods : n/a


Results : n/a


Discussion :

A 35-year-old male presented with slowly progressive back pain, hip pain and proximal muscle weakness over one year, necessitating wheelchair assistance. Lab studies revealed severe hypophosphatemia - 1.7 (nl 2.5-4.5mg/dL), inappropriate phosphaturia, normal serum calcium level, low 25 hydroxy vitamin D of 12 (nl 30-100ng/mL), low 1,25 dihydroxy vitamin D, and normal PTH 76 (nl 18.5-88pg/mL). MRI cervical spine and pelvis showed multifocal insufficiency fractures throughout the pelvis suggestive of a metabolic disorder. Nuclear bone imaging showed diffuse increased activity throughout the rib cage, distal bilateral distal femur and tibia and midportion of both feet.The FGF-23 level was found to be elevated to 219, and when repeated 225 (high normal 215) consistent with probable tumoral production of FGF-23 causing hypophosphatemia. Whole body FDG-PET showed no evidence of metabolically active tumor or metastatic disease. A whole body octreotide scan did not show any evidence of a focal somatostatin positive receptor tumor. He was treated with phosphate, calcitriol and cholecalciferol which improved his symptoms, and he was able to ambulate without assistance. Repeat imaging after 6 months with Octreotide SPECT/CT showed a probable right hip tumor. The tumor site was confirmed by selective venous catheterization with measurement of FGF 23. Although surgical resection was offered, he declined surgery.


Conclusion :

TIO is a paraneoplastic syndrome with a delayed diagnosis, subsequent to a nonspecific clinical presentation and difficulty in tumor localization. Early multimodality imaging may be negative. It is important to have a high index of suspicion, and follow up imaging is essential to diagnose these cases. Octreotide SPECT/ CT is more sensitive and specific for TIO than FDG PET/CT. Selective venous catheterization with measurement of FGF23 may be helpful in identifying causative tumors, especially if multiple suspicious lesions are noted, or for tumors located in areas where surgical excision may be difficult. Wide surgical excision is curative and is the treatment of choice.

SHORT URL FUNCTION-->

Neelam Baral

Resident
Medstar Washington Hospital Center, Maryland

Resident in Internal Medicine, interested in Endocrinology.

Binaya Basyal

Resident
Medstar Washington Hospital Center

Resident in Internal Medicine.

Skand Shekhar

Fellow
NIH

Fellow in Endocrinology

Amy Phillips

Fellow
Medstar Georgetown University Hospital

Fellow in Endocrinology.

Meeta Sharma

Associate Professor
Medstar Washington Hospital Center

Director Diabetes team. Assistent chief -Section of Endocrine

Neelam Baral

Resident
Medstar Washington Hospital Center, Maryland

Resident in Internal Medicine, interested in Endocrinology.