Bariatric Surgery and the Incidence of Rheumatoid Arthritis

A Swedish Obese Subjects Study

Cristina Maglio; Yuan Zhang; Markku Peltonen; Johanna Andersson-Assarsson; Per-Arne Svensson; Christian Herder; Anna Rudin; Lena Carlsson


Rheumatology. 2020;59(2):303-309. 

In This Article


Baseline Characteristics

We identified a total of 11 individuals with prevalent RA at baseline, i.e. having a reported diagnosis of RA before baseline. Therefore, after exclusion of the 11 subjects with prevalent RA, this report included 4036 subjects: 2002 from the surgery group and 2034 from the control group. Compared with participants from the control group, subjects in the surgery group had higher BMI, CRP and ESR and were more likely to be smokers, as previously reported.[15] They also were slightly younger compared with participants from the control group (Table 1). As previously reported, bariatric surgery resulted in a sustained rreduction in BMI [−23% (95% CI −24, −23) at the 2 year follow-up; −17% (95% CI −17, −16) at the 10 year follow-up], whereas the change was minimal in the control group [+0.1% (95% CI −0.3, 0.5) at the 2 year follow-up; +1.7% (95% CI −1.0, 2.4) at the 10 year follow-up].[15]

Incidence of RA During Follow-up

Ninety-two participants in the SOS study developed RA during a follow-up for up to 29 years [median follow-up 21 years (range 0–29)]. Baseline characteristics of study participants stratified by incident RA are shown in Table 2. The percentage of men was lower in the group of SOS participants who developed RA compared with those who did not; moreover, participants who developed RA had higher serum levels of CRP at baseline. Of the 92 study participants who developed RA, 51 were seropositive; serostatus was unknown for 17 subjects.

Bariatric Surgery and the Incidence of RA

Among the 92 subjects who developed RA during follow-up, 47 belonged to the surgery group (2.3%) and 45 to the control group (2.2%). Bariatric surgery was not associated with the incidence of RA during follow-up, as shown in Figure 1A (log-rank P = 0.88). Similarly, we could not detect any association between bariatric surgery and RA when only seropositive RA (no = 51) was considered as the outcome in the analysis (log-rank P = 0.52). Although previous studies have shown that the association between higher BMI and development of RA is stronger in women,[6] we could not detect any interaction between bariatric surgery and sex on the incidence of RA (P = 0.92).

Figure 1.

Cumulative incidence of RA in the SOS study
(A) Intention-to-treat analysis. (B) Per-protocol analysis.

We also performed a per-protocol analysis. A total of 285 participants from the control group who underwent bariatric surgery after baseline were censored at the time of the surgery, including two subjects who developed RA after the day of the surgery. Three subjects from the control group developed RA before undergoing bariatric surgery and therefore where not censored. The per-protocol analysis confirmed no association between bariatric surgery and RA (log-rank P = 0.93; Figure 1B).

Multivariable Analysis for the Incidence of RA

In a multivariable analysis including risk factors for RA, bariatric surgery was not associated with the incidence of the disease [intention to treat: HR 0.92 (95% CI 0.59, 1.46), P = 0.74; per protocol: HR 0.86 (95% CI 0.54, 1.38), P = 0.53; Table 3]. Baseline CRP levels were significantly associated with a higher risk of developing RA independently of bariatric surgery and other factors [intention to treat: HR 1.28 (95% CI 1.06, 1.55), P = 0.01; per protocol: HR 1.29 (95% CI 1.07, 1.56), P = 0.007; Table 3]. Smoking was also associated with an increased risk for RA, although the association reached significance only in the per-protocol analysis [intention to treat: HR 1.63 (95% CI 0.99, 2.67), P = 0.05; per protocol: HR 1.69 (95% CI 1.02, 2.81), P = 0.04; Table 3]. Neither sex nor baseline ESR, BMI and obesity duration were risk factors for RA in this cohort of subjects with obesity.

BMI Changes and the Incidence of RA

To determine whether changes in BMI rather than bariatric surgery were associated with the development of RA, we performed a multivariable Cox regression analysis including BMI change at the 2 year follow-up, sex, age, ESR, CRP and smoking. Changes in BMI at the 2 year follow-up were not associated with the development of RA in the intention-to-treat analysis or the per-protocol analysis [HR 0.96 (95% CI 0.82, 1.12), P = 0.57 and HR 0.99 (95% CI 0.83, 1.17), P = 0.87, respectively].