Decoding the Data: Early Biologic Use and Psoriatic Arthritis

Announcer:
This is Living Rheum on ReachMD. On this episode, we’ll hear from Dr. Laura Coates, who will be reviewing evidence on biologic therapy in psoriasis and its impact on psoriatic arthritis risk. Dr. Coates is an NIHR Research Professor and Senior Clinical Research Fellow at the University of Oxford in the United Kingdom.

Here she is now.

Dr. Coates: 
When this concept of intervening early in psoriasis to try and prevent the development of psoriatic arthritis came up, there’s a good opportunity to look at data from people who have psoriasis and who have gotten treated with biologic agents as part of their standard care to treat their skin disease, but also look at whether maybe that's having an impact on the chance of them developing psoriatic arthritis.

So there've now been a lot of studies published looking at this, and they're using electronic health records—routine data that's collected in hospitals day to day—to look at patients who have psoriasis who get started on a biologic, and see if after that time point they develop psoriatic arthritis, and we can see that they have that diagnosis.

There've been a number of studies that have looked at comparing people who are receiving biologic drugs to those who are receiving other treatment: topical therapy like creams, phototherapy for psoriasis, or cheaper tablet medications like methotrexate. Some of them have suggested that the use of biologics reduces the chance of those patients developing psoriatic arthritis when compared to patients getting phototherapy or conventional drugs.

But it's obviously really tricky, because this isn't a randomized control trial. Patients were not equally allocated to these two different treatments. There's gonna be loads of different reasons why the dermatologist in their clinic put this particular patient on a biologic, but the next patient on phototherapy. So the patients are going to be different, so we need to try and account for that when we are studying this data.

The other thing that we see that was demonstrated really nicely in a paper from University of Pennsylvania was that, often, we are seeing a bias, because somebody's seen a dermatologist and got put on a biologic. So you see your dermatologist, you mention that you have joint pain, and you get started on a biologic predominantly for your skin, but obviously, the dermatologist hopes it's gonna help with your joint pain as well. And at the same time, they say, “Oh, you should see a rheumatologist because you might have psoriatic arthritis.”

And then one month later, or three months later, or six months later—depending on how quickly you get that appointment through—you see a rheumatologist and you get diagnosed with PsA. And it looks like the biologic just predated you developing arthritis, and maybe it caused your psoriatic arthritis, but of course, that's not the case at all. You were about to develop or developing— maybe even already had psoriatic arthritis—and the biologic has probably made things better. But the diagnosis was only made after you started the treatment. And that's what's called protopathic bias, where being seen and being started on that treatment actually also triggers you getting a diagnosis of psoriatic arthritis.