Unintentional unblinding in rheumatic disease trials

The practice of blinding treatment assignment in randomised controlled trials mitigates important biases in observational studies. Unblinding, whereby study participants or investigators become aware of treatment assignments, is an important threat to the validity of trial results. Rheumatology studies might be particularly susceptible to unblinding because rheumatic disease therapies often cause high rates of idiosyncratic side-effects and frequently rely on subjective endpoints. Despite this susceptibility, the degree to which unblinding occurs in randomised controlled trials in rheumatic diseases has rarely been assessed during trials or acknowledged as a limitation. Rheumatologists should be aware of this important threat to the validity of trial results, assessments of unblinding should be undertaken, and strategies to prevent unblinding should be deployed when feasible.