Expert panelists discuss the association and increased risk between psoriasis, psoriatic arthritis, and metabolic syndrome.
Peter L. Salgo, MD: There’s also psoriatic arthritis, which you’ve got to throw into this mix.
Joel Gelfand, MD, MSCE, FAAD: Yes.
Peter L. Salgo, MD: What is the incidence of that, all-comers with psoriasis?
Joel Gelfand, MD, MSCE, FAAD: All-comers, it’s about 10% of all patients with psoriasis with develop psoriatic arthritis. But that frequency increases the more significant your skin disease is. So, as your disease gets more extensive on the skin, the odds of developing psoriatic arthritis increase as well. Roughly 30% to 40% of people who have more severe psoriasis, based on body surface area, will develop psoriatic arthritis. But one of our challenges in the clinic is that the correlation between how bad your skin disease is and how bad your joint disease is, is actually pretty weak. And so people who have very minor or mild skin disease with very severe joint disease, it can be disabling, and that’s often the case. But in the general population, most people tend to have more mild skin disease.
Peter L. Salgo, MD: I’ll tell you, some of the scariest x-rays I’ve ever seen are the people with psoriatic arthritis.
Steven Feldman, MD, PhD: Yes. Before we delve too deeply into arthritis, I don’t think we should leave people watching this or an insurer, God forbid, with the idea that the skin involvement is an optical or cosmetic issue. That is far from the case. The disease itches, it hurts, it’s socially disabling. Even without the arthritis, the skin disease is a bad thing to have.
Peter L. Salgo, MD: No, I didn’t mean to say it wasn’t. In fact, isn’t that one of the problems with dermatology as a specialty? People say, “Oh, it’s just dermatology.” But it’s not—this is a real disabling disease.
Steven Feldman, MD, PhD: Yes. And I think even dermatologists underestimate it.
Peter L. Salgo, MD: Really?
Steven Feldman, MD, PhD: I think it’s really great for doctors to be sick every now and then, to understand what your patients are going through. I look at psoriasis all day, and I think nothing of it. If I get just a little irritation in my axilla, in my armpit, I’m like, “Oh man, this is really annoying.”
Joel Gelfand, MD, MSCE, FAAD: Try a little poison ivy for a weekend. That’s how our patients often feel for life.
Peter L. Salgo, MD: Been there, done that.
Joel Gelfand, MD, MSCE, FAAD: I’m really glad Steve expanded on this point. The patients complain of pain, burning in the skin, cracking of the skin, bleeding skin. If they’re wearing a white shirt, they’ll be speckled with blood.
Peter L. Salgo, MD: Oh boy.
Joel Gelfand, MD, MSCE, FAAD: Underneath their shirt. And patients who have more extensive psoriasis where they’ve put on a lot of topical creams to try and control the scaling, they may spend an hour or more a day just trying to manage signs and symptoms of their disease, which is an enormous burden for people.
Peter L. Salgo, MD: It’s interesting what you say. Everything is an objective problem that you can objectify as a doctor until it’s you or in my case, with smaller kids, until it’s my kid. I’m great until my kid gets a hangnail and then my God, the sky is falling. It’s a very interesting point. Now, we did start this broadcast by talking about 2 things. One is psoriasis and 1 is metabolic syndrome. And I must tell you that in researching this broadcast today, when I began I was unaware of this relationship. So why don’t we start by defining metabolic syndrome and then go on to this relationship.
Joel Gelfand, MD, MSCE, FAAD: First of all, I think this is a really good topic, and it’s fascinating that you’re sort of new to it as well.
Peter L. Salgo, MD: Right.
Joel Gelfand, MD, MSCE, FAAD: There’s been a lot of research in this area that shows how necessary these discussions are to educate our peers about it. Metabolic syndrome essentially is a constellation of cardiovascular type risk factors—insulin resistance, dyslipidemia, central obesity, things of that nature. Now, more broadly speaking, psoriasis is a Th1 [T helper cell type 1], Th17 inflammatory disease. We know those inflammatory pathways tend to be shared by cardiometabolic conditions that could promote insulin resistance, promote atherosclerotic disease. And so what the research has shown over the last 2 decades is that if you have psoriasis, you’re more likely to develop things like metabolic syndrome, diabetes, and then major cardiovascular events leading to premature mortality. This is especially the case in people who have more extensive disease. The worse your disease is, the stronger the relationship is of these outcomes.
Peter L. Salgo, MD: I can tell you I know what our viewers are thinking, so I will express it for them, which is there’s a lot of metabolic syndrome out there. People in America—I’ll just be really flat out—people in America are too heavy, right? And there’s a lot of metabolic syndrome based on our diet, lack of activity. Couldn’t it be that when you get severe psoriasis and you don’t move well and you’re sedate, that’s just coincidence? Is there really some relationship?
Joel Gelfand, MD, MSCE, FAAD: There are a couple of pieces of information we have that will lead us away from that hypothesis. One is, some of this is large epidemiological studies where we can control risk factors. You can show that people with psoriasis are more likely to develop diabetes independent of their body mass index and at higher rates than people with say rheumatoid arthritis. You can do some controlled studies in that way. Interestingly, there have been some recent randomization genetic type studies showing that the genetics of obesity seemed to be causally related to developing psoriasis.
Peter L. Salgo, MD: Really?
Joel Gelfand, MD, MSCE, FAAD: And that suggested a causal relationship between the 2 disease states.
Peter L. Salgo, MD: We’re talking about Th1, Th17 again?
Joel Gelfand, MD, MSCE, FAAD: That’s correct.
Peter L. Salgo, MD: Which they overlap and share?
Joel Gelfand, MD, MSCE, FAAD: That’s right. And then the other thing that’s really interesting is some mouse models of psoriasis where, if you take a mouse and you give it psoriasis just in its skin, these mice eventually develop metabolic disorders, essentially aortic diseases, thrombosis, things of that nature.
Peter L. Salgo, MD: I never thought someone could make me feel sorry for a mouse, but you just did.
Steven Feldman, MD, PhD: The association in teasing it out is complicated because if you have horrible psoriasis, especially if your joints are hurting, you may be more sedentary.
Peter L. Salgo, MD: Well, that’s what I was alluding to.
Steven Feldman, MD, PhD: If you feel socially disabled by having these lesions all over, you may be less likely to go to the pool, or the gym. You may sit at home depressed watching television, eating potato chips, drinking beer, maybe smoking with a third hand. So on the one hand, I think it’s become clear there are these genetic components that lead these, but there may be behavioral issues.
Peter L. Salgo, MD: It’s not binary is what you’re saying. And you told me that to control for this, there were some other genetically mediated diseases that affect mobility, such as rheumatoid arthritis.
Joel Gelfand, MD, MSCE, FAAD: First of all, it’s always hard to establish pure causal relationships in these type of studies, right? And I think Steve’s point is really important, that these things are multifactorial, which means there has to be a multifactorial plan to deal with these associations that we see in terms of bettering people’s health.