The need for strategies to address obesity and psoriatic arthritis prevention in psoriasis
Authors: A. Ogdie, L. Eder
Journal: British Journal of Dermatology (2020)

Linked Article: Green et al. Br J Dermatol 2020; 182:714–720. A handful of studies have now identified obesity as a risk factor for development of psoriatic arthritis (PsA).1 However, establishing a causative role of any particular risk factor is challenging. While randomized controlled trials are the gold standard for establishing causation, observational studies are often the first step in supporting causation by demonstrating a temporal association and a dose effect, reflecting that a change in the level of the exposure leads to a difference in outcome.2 In this issue of the BJD, Green et al. found that, among obese or overweight individuals with psoriasis, reductions in body mass index were associated with a reduced risk for PsA. In demonstrating that changing the level of the risk factor (i.e. body mass index) changes the outcome, this study provides further supporting obesity as a causal risk factor for PsA.3 Now comes the hard work: putting this knowledge into action. This new evidence supports two important future needs: (i) the need for mechanisms to help our patients to lose weight and (ii) the need for PsA prevention trials in psoriasis. Obesity is a common problem in psoriasis and PsA.4-6 Patients with PsA and/or psoriasis are more obese than the general population across multiple cohorts. Obesity has not only been demonstrated to be a risk factor for both psoriasis and PsA, but it is also associated with having more severe disease, diminished response to therapy and increased adverse outcomes with methotrexate.5, 7 Furthermore, obesity is associated with diabetes, hyperlipidaemia, hypertension, metabolic syndrome, nonalcoholic fatty liver disease and increased risk for cardiovascular events.4-6, 8-10 Clearly, there is ample evidence to demonstrate that obesity is bad. Increasingly, there is also a body of evidence supporting weight loss as an effective treatment for patients with psoriasis, as reviewed recently by Mahil et al.11, 12 And, for further fodder, we now also know from Green et al. that weight loss is associated with a lower risk for PsA. So, we have the evidence to tell our patients why they should lose weight but we still lack the tools to help them actually achieve and maintain weight loss. Dermatologists and rheumatologists are generally not trained in supporting weight loss. Even primary care physicians struggle with helping patients through weight loss. While referral to a nutritionist is an option, accessibility and insurance/healthcare coverage remain an important problem across multiple health systems. Alternatively, patients can be referred to an existing programme like Weight Watchers, or a similar online program or mobile app can be helpful (there are now many that can help track calories such as MyFitnessPal and Lose It!). However, most often, if the importance of weight loss is discussed, the patient is left to figure out how to accomplish this goal on their own. This is an opportunity lost and one that can be harnessed through development of resources specific to psoriatic disease. If we simply tell a patient why they need to lose weight without giving them the tools, most people will not act. Present bias, a concept addressed by behavioural economics, explains that people are primarily concerned with short-term rewards.13 Rewards in the future are 'discounted' and mean less to the individual than a short-term win. In fact, sometimes the short-term 'win' is sitting on the couch to watch another show and waiting for tomorrow to start the diet or physical activity programme. In other words, educating the patient about the long-term benefits of weight loss (i.e. decreasing the risk for PsA or cardiovascular outcomes) is only so helpful, because the rewards are so far off in the future that they are heavily discounted. Present bias can be overcome through a variety of interventions including short-term incentives, commitment contracts and other methods that provide support for starting now and continuing to move forward one step or one meal at a time. As dermatologists and rheumatologists, we need programmes that we can refer our patients to that will help them get started right away and that address the barriers they face in attaining, and then sustaining, weight loss. One of the key questions addressed by Green et al. is 'can we prevent PsA?'. The next decade will see many studies addressing this question. This question is increasingly important as we continue to struggle to attain the level of response to therapy seen in skin psoriasis within the joints in PsA. Given that we cannot get most patients to remission once they have clinically overt PsA, we can flip the question and alternatively target preventing the onset of PsA.1 Observational studies such as the one by Green et al. are critically important for defining the types of interventions that may be studied in future randomized prevention trials. However, observational studies are still plagued by potential confounding. In other words, patients who lost weight could have made a positive lifestyle change (e.g. a dietary change) that was associated with the decreased risk for PsA rather than weight loss specifically, or they could have lost weight for unhealthy reasons (e.g. cancer) leading to premature death (a potential competing risk). Thus, trials are needed to address whether the weight loss, or other interventions such as early treatment of psoriasis, are significantly associated with reduced risk for development of PsA. Prevention trials are challenging as they require large numbers of patients followed over extended periods of time, particularly given the relatively low yearly rate of conversion to PsA among all patients with psoriasis.14 Testing prevention concepts in 'high risk' populations is a potential solution to the low incidence of PsA but requires further studies to quantify the relative importance of risk factors. Additionally, networks of patients with psoriasis in centres with dermatologists and rheumatologists will be needed in order to carry out such trials. Finally, definitions of the outcomes (e.g. PsA by rheumatologist diagnosis or CASPAR criteria) and surrogate outcomes (e.g. imaging outcomes) will be critical to the success and clinical relevance of the trial findings. Thus, there is still much work to be done to get such trials off the ground.1 In summary, the manuscript by Green et al. adds to the evidence that obesity is an important risk factor for PsA and supports weight reduction as a potential means for reducing this risk. With this evidence, we now need programmes to help patients with psoriasis lose weight, not only to reduce the risk for PsA but also to achieve the many known benefits of weight loss in psoriatic disease. Additionally, future trials are needed to address weight loss as an intervention to improve risk for PsA as well as other interventions to prevent PsA.