The Correlation Between BMI and TNF Inhibitor Response in Ankylosing Spondylitis

By Spondylitis Association of America

Wednesday, September 20, 2017

One of the larger challenges involved in treating ankylosing spondylitis (AS) is the varying effects of, and responses to, available medications. Currently, Tumor Necrosis Factors (TNF) inhibitors are the standard of care for most patients with moderate to severe AS, and, as with any form of organic medication, their effectiveness can be influenced by various biological factors.

A recent study published in The Journal of Rheumatology, suggests that body mass index (BMI) is one of these biological factors that can affect a person’s response to anti-TNF therapy. The study aimed to investigate the idea that individuals with higher body fat content may experience lower overall levels of clinical improvement in response to TNF inhibitors.

The Study

The study was conducted on a pool of 41 AS patients who had not taken TNF inhibitors in the past; 61% of the study group being male. They were then administered adalimumab or etanercept over the course of six months or longer, with continual BMI assessments. After normalizing data to account for age and sex, it was determined that those with a higher body fat percentage and fat mass experienced a lower probability of clinical recovery with TNF inhibitors as well as a decreased response to the medications. Post-treatment analysis of the patients indicated that TNF inhibitors had very little to no effect on body composition in both men and women, though slight muscle recovery was identified as a trend in men.

The reasoning behind the loss of clinical improvement in overweight and obese AS patients is still unclear. It has been hypothesized that the extra body fat in overweight individuals produces pro-inflammatory cytokines that counteract the effects of TNF inhibitors. The authors plan to investigate fat metabolism in the near future and explore additional possibilities.

Sources Used for further reading:
Rheumatology Advisor
The Journal of Rheumatology

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