False-Positive ⁶⁸Ga-DOTATATE PET/CT Findings in Hereditary Hypophosphatemia–Osteomalacia Mimicking Culprit Lesions of Tumor-Induced Osteomalacia

DISCUSSION

⁶⁸Ga-DOTATATE PET/CT is an important noninvasive imaging modality for detection and localization of the culprit lesion of TIO. Other than in tumors, SSTR expression is observed in inflammatory or granulomatous conditions and in fractures or degenerative bone disease, leading to false-positive scan findings in various oncologic cases (1–4). A raised level of FGF-23 is not specific to TIO and can also be found in hereditary hypophosphatemia- and osteomalacia-inducing musculoskeletal disorders, such as X-linked hypophosphatemic rickets and autosomal dominant and recessive hypophosphatemic rickets (5). Our patient presented with long-standing systemic symptoms of hypophosphatemia, with a raised level of FGF-23. ⁶⁸Ga-DOTATATE PET/CT was considered to localize the culprit lesion of TIO in view of the clinically symptomatic and biochemically proven case of hypophosphatemia with an increased FGF-23 level. Increased SSTR uptake was seen in the maxillary sinus and bilaterally in the tibial regions, which on MRI were illustrative of benign etiopathologies. Finally, the patient was diagnosed with hereditary hypophosphatemia caused by the autosomal recessive disorder Fanconi–Bickel syndrome.