Abstract: Primary outcome measure: one cross-over trial including 18 participants showed after four weeks, 2 (95% confidence interval (CI) 0.9 to 3.1) points more improvement on an 11-point disability scale with plasma exchange (10 exchanges over four weeks) than with sham exchange. Rapid deterioration after plasma exchange occurred in eight of 12 who had improved. Secondary outcome measures: when we combined the results of this cross-over trial and a trial with 29 participants treated in a parallel-group design, there were 31 points (95% CI 18 to 45) more improvement on an impairment scale (maximum score 280) after plasma exchange (six exchanges over three weeks) than after sham exchange. There were significant improvements in both trials in an electrophysiological measure, the proximally evoked compound muscle action potential, after three or four weeks. Non-randomised evidence indicates that plasma exchange induces adverse events in 3% to 17% of procedures. These events are sometimes serious. Both trials had a low risk of bias. A trial that showed no significant difference in the benefit between plasma exchange and intravenous immunoglobulin is included in the Cochrane review of intravenous immunoglobulin for this condition. Moderate- to high-quality evidence from two small trials shows that plasma exchange provides significant short-term improvement in disability, clinical impairment, and motor nerve conduction velocity in CIDP but rapid deterioration may occur afterwards. Adverse events related to difficulty with venous access, use of citrate, and haemodynamic changes are not uncommon. We need more research to identify agents that will prolong the beneficial action of plasma exchange.

Plain-language summary: We found two randomised controlled trials. Both studies compared plasma exchange with sham exchange (in which blood was removed and returned but not exchanged). One trial aimed to compare four weeks' plasma exchange with sham exchange. The 18 participants received both treatments, being randomised to either treatment in the first period of the trial, crossing over to the other treatment for the second period. The other trial compared three-weeks' plasma exchange in 15 participants with sham exchange in 14 participants. We considered both trials at low risk of bias, which means largely free of flaws that could have influenced the results. A charitable grant supported the cross-over trial. The other did not report any support. The cross-over trial showed on average two points more improvement on an 11-point disability scale with plasma exchange than sham exchange. This was unlikely to have occurred by chance. The parallel-group trial did not report this outcome. When we combined the results of both trials, plasma exchange produced significantly more improvement in severity of disease signs measured by neurologists than sham exchange. The results reported were short term. In practice, people with CIDP receive repeated courses or combinations of plasma exchange with additional agents. Another Cochrane review includes a trial showing similar improvement after plasma exchange to that after intravenous infusion of immunoglobulin (the antibody portion of blood). According to non-randomised evidence, plasma exchange causes adverse events in 3% to 17% of procedures. These are sometimes serious. Because of the small size of the only trial reporting changes in disability, the quality of the evidence that plasma exchange reduces disability is moderate. The quality of the evidence that plasma exchange improves the signs of disease measured by a neurologist is high. The evidence is up to date to 30 June 2015.