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RESEARCH PRODUCT

Osteoprotegerin: a new biomarker for impaired bone metabolism in complex regional pain syndrome?

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Abstract Osteoprotegerin (OPG) is important for bone remodeling and may contribute to complex regional pain syndrome (CRPS) pathophysiology. We aimed to assess the value of OPG as a biomarker for CRPS and a possible correlation with radiotracer uptake in 3-phase bone scintigraphy (TPBS). OPG levels were analyzed in 23 CRPS patients (17 women; mean age 50 ± 9.0 years; disease duration: 12 weeks [IQR 8–24]), 10 controls (6 women; mean age 58 ± 9.6 years) and 21 patients after uncomplicated fractures (12 women; mean age: 43 ± 15 years; time after fracture: 15 weeks [IQR: 6–22]). The CRPS and control patients also underwent TPBS. OPG in CRPS patients was significantly increased by comparison with both control groups (P = 0.001; Kruskal-Wallis test; CRPS patients: 74.1 pg/mL [IQR: 47.1–100.7]; controls: 46.7 pg/mL [IQR: 35.5–55.0]; P = 0.004; fracture patients: 45.9 pg/mL [IQR: 37.5–56.7]; P = 0.001). As a diagnostic test for CRPS, OPG had a sensitivity of 0.74, specificity of 0.80, positive predictive value of 68% and negative predictive value of 84%. Receiver operating characteristic curve analysis showed an area under the curve of 0.80 (CI: 0.68–0.91). For the CRPS-affected hand, a significant correlation between OPG and TPBS region of interest analysis in phase III was detected (carpal bones; r = 0.391; P = 0.03). The persistent OPG increase in CRPS indicates enhanced osteoblastic activity shown by increased radiotracer uptake in TPBS phase III. A contribution of bone turnover to CRPS pathophysiology is likely. OPG might be useful as a biomarker for CRPS.