SAT245 Hips Don’t Lie: A Case Of Peri-Prosthetic Pseudotumor Leading To Hypercalcemia After Total Hip Replacement

Disclosure: F. Sotomayor: None. H. Whitlatch: None. Background: Peri-prosthetic pseudotumors are well described, yet rare complications of total hip replacement. They can present as destructive or granulomatous lesions. We present the first documented case of 1,25 vitamin D-mediated severe hypercalcemia caused by a periprosthetic granuloma. Case: A 62-year-old man with a history of osteoporosis, ankylosing spondylitis presented with hypercalcemia (calcium 12.2 mg/dL) on routine laboratory testing. He had a history of bilateral cement hip arthroplasty in 1981 followed by multiple bilateral revisions - three revisions of left hip arthroplasty, one revision of right hip arthropasty. Biochemical evaluation included PTH 5 pg/mL (8 - 54 pg/mL), PTHrP 2.7 pmol/L (0.0 - 2.3 pmol/L), vitamin D-25 59 ng/mL (20-80 ng/mL), a negative Quantiferon TB Gold, and normal serum protein electrophoresis. 1,25 Vitamin D was elevated at 280.5 pg/mL (19.9-79.3 pg/mL). During investigation of 1,25 vitamin D-mediated hypercalcemia, he received a dose of zoledronic acid with transient improvement in hypercalcemia. ACE was negative and CT chest and abdomen was without evidence of granulomatous disease. A whole-body PET scan showed increased metabolic activity surrounding the right femoral and acetabular components with a broad zone of osteolysis in the proximal femur and increased metabolic activity surrounding the left greater trochanter. These findings were concerning for inflammatory granuloma formation. He was prescribed prednisone 30 mg daily with rapid normalization of serum calcium. Prednisone was gradually tapered to 10 mg daily with maintenance of normocalcemia. Discussion: Pseudotumors are an uncommon complication of total hip arthroplasty. These are described as non-infectious and non-neoplastic adverse soft tissue reactions to implants. They manifest as destructive or granulomatous periprosthetic lesion. They cause osteolysis, erosions, pathological fractures, and dislocations. Their formation is due to foreign body reaction to polyethylene, methylmethacrylate, cement or metal adjacent to the joint implant. Associated inflammation leads to macrophage activation, prostaglandin release, and osteolysis. Histologically, they are characterized by the presence of macrophages, extensive coagulation necrosis, lymphocytes, eosinophilic infiltration and granulomatous reaction. While non-malignant, they can cause extensive bony destruction and may require complex revision surgery. T