Predictors of a placebo response in patients with hand osteoarthritis: post-hoc analysis of two randomized controlled trials

Abstract

Background Placebo can have a significant therapeutic effect in patients with hand osteoarthritis (OA). This aim of the study is to identify factors associated with a clinically meaningful placebo response in patients with hand OA. Methods This post-hoc analysis of two double-blind, placebo-controlled, randomized trials (RCTs) investigating the efficacy of GCSB-5 or diacerein as treatments for hand OA analyzed the efficacy of a placebo. Clinical and laboratory factors associated with a clinically meaningful response, defined as an improvement in the Australian/Canadian Osteoarthritis Hand Index (AUSCAN) pain score\u2009>\u200910 at 4\u2009weeks relative to baseline, were identified. Results The mean improvement in the AUSCAN pain score was −\u20096.0\u2009±\u200920.3, with marked variation between 143 hand OA patients (range: −\u200976.4 to 33.2). A clinically meaningful improvement was observed in 54 (37.8%) patients. Placebo responders had worse AUSCAN pain scores (55.7\u2009±\u200919.7 vs. 43.6\u2009±\u200921.6, p \xa0=\u20090.001) and a worse AUSCAN stiffness (68.2\u2009±\u200920.5 vs. 57.5\u2009±\u200924.5, p \xa0=\u20090.008) at baseline than non-responders. Improvements in pain correlated with the baseline pain level (Pearson r \xa0=\u2009−\u2009427, p \xa0<\u20090.001). Structural joint changes such as tender, swollen, enlarged, or deformed joint counts did not differ between placebo responders and non-responders. In a multivariable analysis, only baseline AUSCAN pain was associated with a clinically meaningful placebo response (OR: 1.054, 95% CI [1.019–1.089], p \xa0=\u20090.002). Conclusions High levels of pain at baseline are predictive of a clinically meaningful placebo response in patients with hand OA. Further studies are needed to optimize and utilize the benefit of placebo responses in patients with hand OA.