A Case of Tumor-Induced Osteomalacia: Finding the Culprit
A 43-year-old man with primary hypothyroidism presented for evaluation of progressive fatigue, weakness, muscle, and joint pain in the setting of recurrent fractures. He was first diagnosed with a non-traumatic left ankle fracture at age 41, which was treated conservatively. A few weeks after this diagnosis, he began to experience musculoskeletal pain in several locations including bilateral knees, ankles, left shoulder, left arm, and lower back which affected his overall functional status. He struggled to climb a flight of stairs, often grabbing the railing to pull himself up. A nuclear medicine bone scan showed abnormal uptake in bilateral ribs, vertebrae, right knee, hips, ankles, and feet. A lower extremity MRI showed stress fractures in the left fibula, the fifth metatarsal, and right tibia.

The patient was first seen at our Bone Center in March 2019. Laboratory evaluation showed normal calcium at 9.3 mg/dL, low phosphorus at 1.5 mg/dL, low 1,25-dihydroxyvitamin D at 13 pg/mL, high phosphate excretion fraction in urine (27%), elevated alkaline phosphatase at 163 U/L, and elevated FGF23 at 238 RU/mL (Table 1). The patient started calcitriol and phosphate supplements that significantly improved muscle weakness; however, he continued to have bony pain. Although it is not recommended to perform a biopsy of the presumed lesion due to the risk for tumor cell seeding, the left acetabular lesion was biopsied given concern for metastatic disease. The biopsy results showed: Spindle cell neoplasm present. The patient underwent radical resection of the tumor of the posterior left acetabulum with the reconstruction of the posterior wall and posterior column of the acetabulum through a Kocher-Langenbach approach. His hip joint was able to be spared utilizing a 3D-printed custom bone cutting guide (CG) and intra-operative O-arm guided surgical navigation (Medtronic© Stealth) utilizing a navigated Sonopet Ultrasonic Bone Cutting Bovie (Stryker). The posterior wall and column of his acetabulum were constructed with tantalum augment (Zimmer) and a pelvic reconstruction plate and screw construct (Synthes) after tumor removal.

Postoperatively, he was kept toe-touch weight-bearing for 6 weeks and then advanced to weight-bearing as tolerated over the subsequent 6 weeks. Posterior hip precautions were employed for 3 months postoperatively. Clinical and radiographic follow-up at 6 months postoperatively found him to be pain-free in his left hip, with no evidence of hardware complication, back to hiking and walking on the treadmill. The patient has continued to report improvement in his symptoms, functional status has returned to baseline, with almost complete resolution of bone pain, and no recurrence of fractures. Phosphorus level also remained normal at 3.4 mg/dL 6 months after surgery.

source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8241250/