In all, 663 patients with psoriasis but not PsA before or at initiation of biologic treatment were included in their analysis and matched to a control group of 663 patients with psoriasis who had not received biologic treatment. Propensity score matching was used to iron out some differences in baseline characteristics that had been seen between the groups, such as older age at diagnosis, higher body mass index, and a longer time between diagnosis and treatment seen in patients treated without biologics.
After adjusting for multiple risk factors and confounders, “the control group still had a significantly higher risk for PsA, compared to the biological treatment group,” the researchers wrote. Indeed, the adjusted hazard ratio was 1.39, with a 95% confidence interval between 1.03 and 1.87.
An ‘intriguing study’
“This is a retrospective study, and it has all the faults of a retrospective study,” said Dr. Adebajo, associate medical director for research and development at Barnsley (England) NHS Foundation Trust. But “these were patients who hopefully hadn’t yet developed psoriatic arthritis, although it is difficult to exclude subclinical psoriatic arthritis.”
The ideal would of course be to look at patients prospectively, but a randomized clinical trial would be unlikely to ever be conducted, Dr. Helliwell noted. “It would be unfair to randomize people who have got bad psoriasis and need a biologic to placebo just to prove the point really,” he said. “Getting control groups in this arena is very difficult.”
That doesn’t mean that prospective evaluation is not possible. Dr. Adebajo noted that there were already cohorts of newly diagnosed patients who were being prospectively followed up and those could perhaps be used to look at the question again in the future.
“You’re then looking at the natural history, the natural outcome, and you don’t need to worry about confounding because you’re just collecting all of the information as you go along.”
The idea that biologics might slow or even prevent the onset of PsA is “an interesting and enchanting hypothesis,” Dr. Adebajo said. “The study doesn’t prove the hypothesis, but it’s an intriguing study because it doesn’t disprove the hypothesis either.
“It gives us food for thought and a basis for further studies,” as well as some “encouragement to perhaps use biologics earlier because there may be additional benefits of doing so.”
That’s still to be proven of course, as it has been reported that patients with psoriasis can develop PsA while taking biologics.
“Clinically, that’s what we see in the combined clinic. We get people referred with psoriasis [who are] already on a biologic who developed musculoskeletal problems,” Dr. Helliwell said.
“It would be nice to believe” that biologics prevent or slow PsA in patients with psoriasis, Dr. Helliwell added, but I’m not sure these data are conclusive. From this study we know nothing about the phenotype of psoriasis, which is important in the development of PsA. In addition, we know that of the 30% of people with psoriasis who develop PsA, about half of these are undiagnosed at the time of such studies. In that case, what the biologic is doing is just treating preexisting PsA. If you count those numbers up, some of the differences between the two groups seen in this study are accounted for. From registry data there is no way of checking this.”
No external funding was used for the study. One author acknowledged acting as an investigator, adviser, or consultant to several pharmaceutical companies including AbbVie, Boehringer Ingelheim, Bristol-Myers Squibb, Coherus, Dexcel Pharma, Eli Lilly, Janssen, Novartis, and Pfizer. All other authors had nothing to disclose.
Dr. Helliwell and Dr. Adebajo had no conflicts of interest.