Submitted by: Pritikanta Paul, MD
Edited by: Elliot Bodofsky, MD
Placebo effect in chronic inflammatory demyelinating polyneuropathy: The PATH study and a systematic review
Lewis et al. J Peripher Nerv Syst. 2020 Sep;25 (3) :230-237
Placebos (pharmacologically inert preparations) are used in treatment trials to assess the true effect of trial medication. Placebo responses have been noted in CIDP trials including the most recent PATH trial investigating subcutaneous IVIG as maintenance therapy. A post-hoc analysis of the placebo group in the PATH study was recently published. Although all randomised subjects were proven to deteriorate off IVIG, 37% of the placebo group remained clinically stable on placebo over 6 months. Placebo effect correlated with older age, more severe disease, and yet more stable disease. The authors also performed meta-analyses of placebo controlled CIDP studies and noted the placebo effect was higher when primary outcome is measuring relapse versus measuring improvement.
Age, disease severity, and stability can affect placebo response. Also future CIDP trials should consider how primary endpoint in study design can influence placebo outcome and hence statistical analysis.