Is there an association between serum soluble interleukin-2 receptor levels and syndrome severity in persistent Complex Regional Pain Syndrome?

Objective: A potentially useful biomarker for Complex Regional Pain Syndrome (CRPS) is the serum soluble interleukin-2 receptor (sIL-2R) level, which is a marker for T-cell activation. Elevated serum sIL-2R levels have been described in CRPS patients compared to healthy controls. In T-cell mediated inflammatory diseases such as sarcoidosis and rheumatoid arthritis, the serum sIL-2R levels correlate with disease severity. In this study, we investigate whether an association exists between serum sIL-2R levels in CRPS patients and CRPS severity. Methods: A cross-sectional cohort study was conducted in a tertiary pain referral center in the Netherlands. Adult CRPS patients diagnosed by the IASP criteria were included between October 2018 until October 2022. The main study parameters were serum sIL-2R levels and the CRPS severity score. Results: Fifty-three CRPS patients were included with a mean syndrome duration of 84 months (Q3 – Q1:180 – 48). The majority had persistent CRPS with a syndrome duration >1 year (n ¼ 52, 98%). The median pain Numerical Rating Score (NRS) was 7 (Q3 – Q1: 8 – 5) and the mean CRPS severity score was 11 (SD 6 2.3). The median serum sIL-2R level was 330 U/mL (Q3 – Q1:451 – 256). No statistically significant correlation was observed between serum sIL-2R levels and the CRPS severity score (r _s ¼ 0.15, P ¼ .28). Conclusions: Our findings suggest that serum sIL-2R levels cannot be used as a biomarker for syndrome severity in persistent CRPS (syndrome duration >1 year). Serial measurements of serum sIL-2R from early CRPS to persistent CRPS are needed to investigate whether serum sIL-2R levels can be used to monitor T-cell mediated inflammatory syndrome activity.