Tumor-induced osteomalacia combined with increased bone resorption postoperatively: A case report

Rare tumor-induced osteomalacia (TIO) usually resulted in bone pain, fragility fractures and muscle weakness in clinical, which is caused by the reduced phosphate reabsorption, thus impaired mineralization of the bone matrix and free energy transfer. The specific problems in postsurgical patients are obscure although surgical removal of the tumor is the only definitive treatment. Here, we documented a female TIO patient who suffered more severe bone pain and muscle spasms post-operation. Further, we presented and discussed our explanation for the unexpected symptoms. PATIENT CONCERNS: The main symptoms were whole-body pain and muscle weakness. The patient also presented with osteoporosis and multiple fractures. DIAGNOSIS: Elevated serum fibroblast growth factor 23 (FGF23) level and hypophosphatemia indicated the diagnosis of TIO. Positron emission tomography (PET)/computed tomography (CT) with 68 Ga-DOTATATE located the tumor in the dorsolateral part of the left foot. Histopathological examinations confirmed the diagnosis. INTERVENTIONS: The tumor was surgically removed immediately after the diagnosis of TIO and localization of the tumor. Postoperatively, calcium carbonate supplement treatment was continued. OUTCOMES: Two days after surgery, the serum FGF23 level was decreased to the normal range. Five days after surgery, N-terminal propeptide of type I procollagen and β-CrossLaps (β-CTx) had a remarkable increase. A month after surgery, the patient N-terminal propeptide of type I procollagen and β-CTx levels were decreased obviously, and serum FGF23, phosphate and 24h urinary phosphate were in the normal range. LESSONS: We report a female patient who presented with osteoporosis and fractures. She was found with an elevation of FGF23 and diagnosis with TIO after PET/CT scanning. After surgically removing the tumor, the patient experienced more severe bone pain and muscle spasms. Active bone remodeling might be the reason for the symptoms. Further study will reveal the specific mechanism for this abnormal bone metabolism.