The Importance of Whole Body Imaging in Tumor-Induced Osteomalacia

A 66-yr-old woman was referred to the National Institutes of Health for evaluation of tumor-induced osteomalacia. She had bone pain, fractures, and an elevated fibroblast growth factor 23 (FGF23) (2295 pg/ml; normal, 10–50). Fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) was performed, but she was unable to keep her arms raised above her head, and due to her body habitus, her elbows were excluded from the imaging when her arms were positioned at her side (Fig. 1A). On ¹¹¹In-octreotide scan, a region of uptake was noted at the left elbow on the 4-h whole body scan (Fig. 1B). Targeted images demonstrated the finding more convincingly (Fig. 1, C and D), and magnetic resonance imaging confirmed the presence of a tumor (Fig. 1E). Her phosphate and FGF23 normalized after resection, indicating cure.

Fig. 1.

A, Elbows were excluded on FDG PET/CT (circles). Activity in foot (arrow) was due to fracture. B, Suspicious uptake was seen in the left elbow on the 4-h ¹¹¹In-octreotide scan (arrow). C and D, Targeted images verified this uptake (arrows; D = ¹¹¹In-octreotide fused single photon emission CT/CT). E, Magnetic resonance imaging confirmed a tumor (arrow).

Tumor-induced osteomalacia is a rare endocrine disease due to small tumors that secrete FGF23 (1). Wide surgical excision of the tumor leads to rapid cure, but locating these tumors can be difficult. Multiple imaging modalities such as ¹¹¹In-octreotide scans (2) and FDG PET (3, 4) are often necessary, and in some cases selective venous sampling may also be needed (5). Routine nuclear medicine imaging often excludes the extremities, but because these tumors can occur anywhere in the body, it is important to include the extremities, as was the case here. Clinicians should be aware of the need for literal whole-body imaging and should realize that it is possible that excluded areas could harbor the causative tumor.