In reply
Thank you for the opportunity to respond, and to clear up some misunderstandings.1
The within-subjects arm of our study showed that the SEI scores of the thrice-weekly exposed plaques declined much more than did the scores of the covered and once-weekly exposed plaques. We agree that this suggests that the combined "local plus [any possible] systemic effects" of phototherapy were greater than any "systemic effect alone." However, Gibbs' assertion that there are only 2 ways of interpreting the decrease in the SEI score of the covered plaques is incorrect. He states that this decline must either be "not clinically relevant" or represent "a large systemic therapeutic effect." Psoriasis is a chronic relapsing-remitting condition, and exacerbations can resolve spontaneously. As detailed in our discussion, we would expect mean unexposed psoriasis plaque severity to decrease (regardless of phototherapy) due to the regression to the mean phenomenon, and the fact that these patients were attending thrice-weekly sessions and receiving not just phototherapy, but the accompanying psychological support and encouragement to apply emollients.