RESUMEN
In the last decade, interest has been growing in the relationship between obesity and several other clinical conditions, besides the well-established links between body mass index (BMI) and cardiovascular diseases or cancer. A particular focus has been put on the impact of a higher BMI on immune-mediated diseases such as rheumatoid arthritis (RA) and psoriatic arthritis (PsA). Obesity has been found to be associated with greater arthritis activity and a reduced probability of response to anti-tumor necrosis factor (TNF) agents. On the other hand, weight loss increases the chances of treatment success. Although the direct effect of a higher body mass on drug clearance might in part account for this obesity-related effect, other biological mechanisms could be involved. The evidence of a negative influence of obesity on arthritis treatment is particularly strong as far as anti-TNF inhibition is concerned; on the contrary, the response to biologic agents targeting interleukin-6, cytotoxic T lymphocyte antigen 4, or CD20 seems not to be negatively affected by a higher BMI. In this review, we will consider the main studies investigating the influence of obesity on anti-rheumatic treatment in RA and PsA patients. We will also try to hypothesize about a possible pathogenic explanation of this phenomenon and its role in the choice of an appropriate and personalized therapy.