Low-dose intravenous immunoglobulin treatment for long-standing complex regional pain syndrome: a randomized trial

Background: Two small trials suggest that low-dose intravenous immunoglobulin (IVIg) may improve the symptoms of complex regional pain syndrome (CRPS), a rare posttraumatic pain condition.Objective: To confirm the efficacy of low-dose IVIg compared with placebo in reducing pain during a 6-week period in adult patients who had CRPS from 1 to 5 years. Design: 1:1 parallel, randomized, placebo-controlled, multicenter trial for 6 weeks, with an optional 6-week open extension. Patients were randomly assigned to 1 of 2 study groups between 27 August 2013 and 28 October 2015; the last patient completed follow-up on 21 March 2016. Patients, providers, researchers, and outcome assessors were blinded to treatment assignment. (ISRCTN42179756) Setting: 7 secondary and tertiary care pain management centers in the United Kingdom. Participants: 111 patients with moderate or severe CRPS of 1 to 5 years' duration. Intervention: IVIg, 0.5 g/kg of body weight, or visually indistinguishable placebo of 0.1% albumin in saline on days 1 and 22 after randomization. Measurements: The primary outcome was 24-hour average pain intensity, measured daily between days 6 and 42, on an 11-point (0- to 10-point) rating scale. Secondary outcomes were pain interference and quality of life. Results: The primary analysis sample consisted of 108 eligible patients, 103 of whom had outcome data. Mean (average) pain scores were 6.9 points (SD, 1.5) for placebo and 7.2 points (SD, 1.3) for IVIg. The adjusted difference in means was 0.27 (95% CI, -0.25 to 0.80; P = 0.30), which excluded the prespecified, clinically important difference of -1.2. No statistically significant differences in secondary outcomes were found between the groups. In the open extension, 12 of the 67 patients (18%) who received 2 IVIg infusions had pain reduction of at least 2 points compared with their baseline score. Two patients in the blinded phase (1 in the placebo and 1 in the IVIg group) and 4 in the open IVIg phase had serious events. Limitations: Results do not apply to patients who have had CRPS for less than 1 year or more than 5 years and do not extend to full-dose treatment (for example, 2 g/kg). The study was inadequately powered to detect subgroup effects. Conclusion: Low-dose immunoglobulin treatment for 6 weeks was not effective in relieving pain in patients with moderate to severe CRPS of 1 to 5 years' duration.Primary Funding Source: Medical Research Council/National Institute for Health Research Efficacy and Mechanism Evaluation Program, Pain Relief Foundation, and Biotest United Kingdom.