THU471 Resolution Of Elevated Alkaline Phosphatase After Joint Replacement In Severe Osteoarthritis

Disclosure: J. Rakholiya: None. S. Nagaraj: None. P. Sharma: None. Introduction: Alkaline phosphatase (ALP) elevation is commonly seen in hepatobiliary disorders. Conditions of high turnover such as healing fractures, hyperparathyroidism, Pagets’ disease of the bone, also lead to ALP elevation (1). Osteoarthritis (OA), characterised by degeneration of articular cartilage, joint space narrowing, and osteophyte formation, rarely causes ALP elevation. We present a case of ALP elevation that resolved after the arthritic joint was replaced. Case Presentation: A 60-year-old female with history of bilateral knee OA presented to the endocrinology clinic due to elevated ALP for over a year. She reported chronic fatigue, sleep disturbance, dry skin, hair loss, inability to lose weight and anxiety. ALP level at presentation was 165 U/L. An extensive work-up showed unremarkable serum and ionized calcium, serum phosphorus, parathyroid hormone, vitamin D 25-OH, calcitriol, 24-hour urine calcium, serum protein electrophoresis, and 24-hour urine protein electrophoresis. Dual x-ray absorptiometry (DXA) scan was normal with Fracture risk assessment tool (FRAX) score 5.9% for major osteoporotic fracture and 0.2% for hip fracture. Patient underwent total left knee arthroplasty following which ALP improved from 165 U/L to 135 U/L within 9 weeks of the procedure. Five months later, ALP was elevated (164 U/L) again. She then underwent right knee arthroplasty and ALP dropped to normal level (114 U/L) within 1 week post-surgery. Discussion: We report the rare phenomenon of ALP elevation in severe OA, that resolved after joint replacement. OA is characterised by inflammation mediated cartilage destruction, subchondral bone change, osteophyte formation, and alterations of ligaments and meniscuses. Bone change in severe OA is associated with increased synovial fluid ALP level. However, there is a paucity of literature studying the association of ALP with OA. A cross-sectional study of 3060 patients demonstrated higher serum ALP with symptomatic knee OA. Another study showed higher ALP levels with increased joint stiffness. The ALP elevation was attributed to low grade inflammation causing an inflammatory response in chondrocytes, and osteoarthritic pain. There is a need for more studies to evaluate the utility of serum ALP as a biomarker for severe OA. Presentation: Thursday, June 15, 2023