SAT-722 Asymptomatic Paget's Disease Of Bone Resulting In A Low Trauma Subtrochanteric Fracture With Normal Markers Of Bone Turnover

Abstract Disclosure: K. Baez: None. L. Rouse: None. V.S. Lagari-Libhaber: None. Background: Paget’s disease of bone (PDB) results from increased bone resorption causing lytic lesions during the initial phase, which progresses to a mixed phase of increased disorganized bone formation. In later stages, irregular bone formation predominates and results in sclerotic lesions. Many patients are asymptomatic, so elevated serum alkaline phosphatase (ALP) increases clinical suspicion for PDB. However, delays in diagnosis occur when ALP is normal, increasing risks for fractures. Clinical Case: A 78-year-old male presented after a fall from standing height, resulting in a left subtrochanteric fracture. Patient denied history of fractures, bone pain, steroids, androgen deprivation therapy, alcohol, smoking, and radiotherapy. Initial tests showed ALP of 93 unit/L (38-126 unit/L), phosphorous of 4.9 mg/dL (2.5-4.5 mg/dL), calcium of 8.9 mg/dL (8.4-10.2 mg/dL), albumin of 3.8 g/dL (3.5-5.0 g/dL), 25-OH vitamin D of 17.5 ng/mL, and GFR >90 mL/min/1.73 m2. Lower extremity CT-scan without contrast showed a mottled appearance of the left femoral head, neck, and intertrochanteric region with multiple lytic and blastic lesions. MRI of the left lower extremity without contrast showed a heterogeneous bone marrow of the left femoral head and proximal femur. Bone scan showed polyostotic linear uptake in the subtrochanteric region of the left femur and distal right femur. The patient underwent open reduction and internal fixation with intramedullary nailing of the left femur. Pathology from an intraoperative bone biopsy showed focally active PDB. Serum C-telopeptide (CTx) was 696 pg/mL (n: 87-345 pg/mL), and bone-specific alkaline phosphatase (BALP) was 13.1 mcg/L (n: 7.6-14.9 mcg/L), obtained 10 days after surgery. The patient was discharged with a plan for follow up on alendronate 40 mg daily and ergocalciferol 50,000 international units weekly. Conclusion: This is a unique case of Paget’s disease of a major weight bearing site following fracture of the left subtrochanteric area and surgery. While it is expected that this patient would have manifested elevated markers of bone turnover in the setting of advanced Paget’s disease, this case is unique is that ALP, CTx, and BALP were not significantly elevated despite a fracture and surgical manipulation of a major weight bearing site. Reasons for this may include decreased bone turnover and metabolic activity seen in the late sclerotic phase of PDB, fracture occurring primarily from mechanical weakness in advanced PDB due to a disorganized and sclerotic bone architecture, and laboratory limitations of detecting elevated markers in post-fracture state. Presentation: Saturday, July 12, 2025