TUMOR INDUCED OSTEOMALACIA: A CASE REPORT
Authors:   Consultant Endocrinologist, Bangalore Baptist Hospital, Bengaluru., B. Santosh , Mathews Vahaneyil Jacob ,   Consultant Rheumatologist, Bangalore Baptist Hospital, Bengaluru., V. Anand ,   Resident, Dept. of Medicine, Bangalore Baptist Hospital, Bengaluru., M.B Suman ,   Consultant Orthopaedic Oncologist, Narayana Health City, Bengaluru.
Published: June 2023

Background:Tumor-induced osteomalacia (TIO), which is also known as oncogenic osteomalacia, is an uncommon paraneoplastic syndrome characterized by a renal phosphate loss causing hypophosphatemia, leading to rickets in children and osteomalacia in adults. It is caused by mesenchymal tumors, which secrete FGF-23 (fibroblast growth factor-23) and rarely other phosphotonins. It can present with a wide range of symptoms and there is often a delay in its diagnosis. Early diagnosis is important and surgical excision can cure the disease in most patients, thus preventing the complications.We report a case of TIO, who was diagnosed at an early stage and underwent curative surgery. Case presentation: A 30 years old female presented with pain in both legs, more severe in the left leg since about 1 year. She also had difficulty in walking, low back ache, muscle pain, mild pain in both the knee joints as well. On examination, she had limping gait, muscle power in the left leg was grade 3-4 otherwise, there was no significant findings on examination. Blood investigations showed elevated alkaline phosphatase (ALP)- 387IU/ml, low serum phosphorus- 1.2mg/dl, normal calcium - 9.8mg/dl, 25-OH Vitamin D- 24.69ng/ml, Parathyroid hormone (PTH)- 61pg/ml.Other blood tests were unremarkable. X- rays of both the legs and pelvis showed a classicalpseudo-fracture in proximal part of both the fibulae and proximal part of the right femur. This suggested hypophosphatemicosteomalacia. TmP/GFR was found to be very low (1.4mg/dl), which confirmed renal phosphate wasting. Later we got Fibroblast growth factor â€“ 23 (FGF-23)- 617RU/ml, which was elevated. This confirmed FGF-23 related hypophosphatemicosteomalacia. In view of the patients age, onset of symptoms, lack of family history, absence of dental and hearing abnormalities, we suspected an acquired rather than a genetic cause. The patient underwent whole body Gallium-68 DOTANOC PET scan, which revealed somatostatin receptor expressing soft tissue density lesion in subcutaneous plane in the mid- anterior right leg, suggestive of FGF-23 secreting mesenchymal tumor.The patient was initially treated with replacement dose of oral phosphorus and calcitriol, along with calcium and vitamin D supplements. Later the patient underwent surgery for excision of the tumor in the right leg. The tumor was around 2cm size and the histopathology was suggestive of gaint cell rich tumor- possibly a phosphaturic mesenchymal tumor. Post surgery, the patient had significant improvement in her symptoms, gait improved and pain reduced. The serum phosphorus level was 3.8mg/dl post-operatively. The serum phosphorus level was maintained without phosphorus replacement. The patient was advised to repeat FGF-23 levels, but the patient failed to get it done. Conclusion: The diagnosis of TIO requires high index of suspicion and should always be looked as a differential diagnosis when we are evaluating a patient with osteomalacia. A detailed history and examination followed by a step wise biochemical evaluation and imaging is important to diagnose TIO in early stages. Surgical resection of the causative tumor will lead to definitve cure of the disease in most patients and avoids the complications like osteoporosis and fractures, thus improving the quality of life of the patients.