Prevalence and Incidence of Metabolic Syndrome in a Cohort of Patients with Rheumatoid Arthritis: A Correlation between Body Mass Index and Disease Activity

Rheumatoid Arthritis (RA) is an inflammatory disease associated with high morbidity and increased cardiovascular disease, and Metabolic Syndrome (MS) is understood as a set of metabolic disorders that correlates with obesity and sedentary lifestyle. The aim of this study is to evaluate the prevalence of MS in a cohort of patients with RA and its correlation to specific factors of the disease. A retrospective cohort study was conducted with 283 patients with RA, followed at the Rheumatology Outpatient Clinic of the Hospital de Clínicas de Porto Alegre (HCPA) between 2008 and 2016; 187 continued to be followed and agreed to be reevaluated between January and November 2016. MS was defined according to the National Cholesterol Education Program and disease activity was assessed using the Disease Activity Score (DAS28). Clinical, biochemical, and anthropometric evaluations were conducted. The prevalence of MS in the first evaluation was 43.9% and, after 8 years, 59.4%. Increased waist circumference and blood pressures, elevated triglycerides and low High-Density Lipoprotein were the most frequent features of MS. The DAS28 was significantly lower in the reevaluation (p = 0.006). The prevalence of MS was higher at the end of 8 years; disease activity, as well as blood pressure, decreased during this period. Steroid


Introduction
Rheumatoid Arthritis (RA) is a systemic inflammatory disease that may cause destruction and deformity of the joints and lead to a functional disability whenever it's not properly treated. Patients with RA, especially those with an active disease, have shown a tendency to present abnormal lipid profile with low levels of high-density lipoprotein cholesterol (HDL) and high levels of triglycerides, as well as less insulin sensitivity. These clinical and laboratory findings, along with central obesity and increased blood pressure, embrace the concept of metabolic syndrome (MS), which accelerates the process of atherosclerosis and inflammation in RA patients, duplicating the risk of fatal and non-fatal cardiovascular events [1] [2] [3] [4].
Accordingly, RA and MS are considered diseases with common characteristics that may increase the risk of cardiovascular disease. Higher rates of insulin resistance and MS have been reported in patients with RA, with the rate of MS found in RA patients ranging from 14% to 56%. This wide variation can be explained by the disparity among the multiple definitions of MS, as well as differences in ethnicity, geographical area, study design and population studied [5]. The aim of the treatment for RA is remission. Moreover, the pillar treatment of synthetic or biological disease-modifying antirheumatic drugs (DMARDs) is the main responsible for reducing or reversing signs and symptoms that interfere with quality of life, disability and progression of joint damage [6]. Appropriate management may enable lower rates of disease activity, resulting in increased functional capacity and better quality of life. Early diagnosis and treatment of RA can also decrease the risk factors for MS, improving quality of life and life expectancy [6].
The aim of this study was to evaluate the components of MS in patients with RA during a long-term follow-up, as well as to correlate the variation with clinical and laboratory parameters of the disease.

Patients and Study Design
A retrospective cohort of 283 RA patients previously described in Cunha et al. [7] was followed at the Rheumatology Outpatient Clinic of the Hospital de Clínicas de Porto Alegre (HCPA) between 2008 and 2016. All of them fulfilled the criteria of the American College of Rheumatology (ACR) for AR and were aged at least 18 years. Patients with another connective tissue disease (except for secondary Sjögren's syndrome) were excluded. Among them, 187 subjects were

Assessment
The patients were scheduled for evaluation, by two different trained researchers at both times, and following the protocol established: clinical, anthropometric, biochemical evaluation; blood pressure measurement; assessment of disease activity.
Clinical evaluation: A questionnaire designed by the authors of Cunha et al. [7] was completed about age, time since diagnosis, current medications and previous diagnosis of cardiovascular disease (CVD)-angina, acute myocardial infarction and stroke. Blood pressure (BP) was registered as the mean of two consecutive measurements, before and after the interview. It is available at the Supplementary Appendix.
Anthropometric evaluation: Weight was registered in kilograms (kg) and height in meters (m). The measurements were carried out as recommended by the World Health Organization [9]. Weight and height were used to calculate the Body Mass Index (BMI) = Weight/Height 2 , classified according to the WHO [10]. Waist Circumference (WC) was measured between the anterior superior iliac spine and the last rib. The measuring instrument used was in centimeters presenting variation of the scale in millimeters (mm) [11].
Laboratory Tests: Total Cholesterol, HDL-c, Triglycerides, Fasting Glucose, Fasting Insulin and ultrasensitive C-Reactive Protein (CRP) were tested in the clinical laboratory of the HCPA. LDL-c was obtained by the Friedewald formula: LDL-c = (TC − HDL-c − TG/5); when serum TG < 400 mg/dl [10]. Insulin resistance (IR) was assessed by calculating the HOMA index = fasting glucose × 0.0555 × fasting insulin/22.59 and the result was considered positive when >2.114 [12], only when TG > 400 mg/dl. RA Activity: According to the Disease Activity Score-28 (DAS-28), an instrument dedicated to evaluating disease activity, activity is considered high when the result is >5.1; moderate between 3.2 and 5.1; low ≤ 3.2, and remission when ≤ 2.6 [13]. DAS-28 was calculated using erythrocyte sedimentation rate (ESR) and four variables (tender joints, swollen joints, ESR and visual analog scale or VAS).
Diagnosis of MS: The NCEP ATPIII 7 criteria were adopted. It required the presence of three or more of the following conditions: waist circumference > 102 cm in men or >88 cm in women, high density lipoprotein cholesterol (HDL-C) < 50 mg/dL in women and <40 mg/dL in men or on drug treatment, triglycerides 150 mg/dL or on drug treatment, blood pressure (BP) 130/85 mmHg or on anti-hypertensive treatment, and fasting glucose 100 mg/dL or on anti-diabetic drug treatment.
Medications: The use of Disease-Modifying Anti-Rheumatic Drugs (DMARDs) was evaluated retrospectively by the patients' medical records and direct interviews.

Potential Bias
In order to avoid evaluation bias for the variables of higher subjectivity, such as DAS-28 and measurements of the hip and abdomen circumferences, the same investigator assessed the patient in 2008 and 2016.

Statistical Analysis
Data were analyzed using the Statistical Package for Social Sciences (SPSS) version 21.0. P ≤ 0.05 was considered significant.
The normality of the quantitative variables was verified using the Kolmogorov-Smirmov test, for the definition of parametric or non-parametric results.
The deltas of the studied variables were constructed using the difference between the two evaluations.
Qualitative variables were determined by absolute and relative frequency, while quantitative variables were determined by the mean and standard deviation or interquartile range and median.
In order to compare the time-points (1 st and 2 nd evaluations) of the variables, the Student's t-test was used for paired samples. In case of asymmetry, the Wilcoxon test was applied. For categorical variables, the McNemar test was used.
So as to compare means among the four groups of Metabolic Syndrome, the One-way Analysis of Variance (ANOVA) in conjunction with the Tukey's range test was applied. In case of asymmetry, the Kruskal-Wallis and Dunn tests were used, respectively. For the comparison of categorical variables, Pearson's chisquare test was applied.
Pearson's correlation was carried out in order to verify the degree of correlation among the variables.
For the correction of confounding factors (age at 1 st evaluation, gender, BMI variation, CRP at 1 st evaluation, DAS-28 at 1 st evaluation, HAQ at 1 st evaluation, use of prednisone at 1 st evaluation and dose of prednisone at 1 st evaluation), multivariate Poisson Regression analysis was used. A p value < 0.20 in the biva-S. F. Krampe et al. riate analysis met the criteria to enter the variable in the multivariate model.
For this study, no sample size calculation was performed because the same patients from the cohort studied by Cunha et al. [7] were reevaluated, verifying the same data and current laboratory tests.

Ethical Approval
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
This study was approved to the local Ethics Committee of Hospital de Clínicas de Porto Alegre number 2014-0602.

Informed Consent
Informed consent was obtained from all participants included in the study.

Results
Among the 187 patients evaluated, 29 (15.5%) were men and 158 (84.5%), women. The mean age at onset was 53.5 years; the sample was mostly of Caucasians (85%); andthey mostly presented a low level of education (complete or incomplete Elementary School: 72%). The sample characteristics are described in Table 1.
When we evaluated the risk factors for MS (    the first evaluation (in spite of having developed or not MS at the second evaluation). It was also noted that patients who remained with MS in both evaluations were those with the highest BMI in both the first and second evaluations (29.7 ± 5.3 and 29.1 ± 5.2 mg/k 2 , respectively, p > 0.05). There was a significant increase in BMI in those patients who did not have MS and developed it during the follow-up period (26.1 ± 3.1 and 27.5 ± 3.8, delta 1.38 ± 3.31, p < 0.05). In this group, DAS-28 was significantly higher, as well as the dose of prednisone.
Since the group that developed MS along the follow-up presented significant differences in the analyzes of Table 4, a multivariate model was conducted in order to investigate possible risk factors for this specific condition, considering that the group that improved (no longer had MS) had a very small number of patients (n = 9). After adjustment by the multivariate model, significance remained for these following outcomes: variation of BMI (RR 1.12, 95% CI 1.02 -1.23, p = 0.018), CRP (RR 1.01, 95% CI 1.00 -1.02, P = 0.001), DAS-28 (RR 2.15, 95% CI 1.03 -4.48, p = 0.041) and dose of prednisone in the 1 st evaluation (RR 1.05, 95% CI 1.02 -1.08, p = 0.001) ( Table 5).
For patients who increased 1 kg/m 2 in BMI after eight years of follow-up, there was a 12% increase in the incidence of MS. Although CRP showed statistical significance, it did not remain significant when the 95% CI was considered. In addition, patients who had moderate/high disease activity in the 1 st evaluation had 115% increased risk of developing MS, even though it has to be considered that the confidence interval was quite wide (95% CI 1.03 -4.48, p = 0.041). Finally, with each increase of one unit in the dose of prednisone taken in the 1 st evaluation, there was a 5% increase in the chance of developing MS.
When comparing the use of drugs with the improvement of the disease activity, only the use of biological drugs was significantly associated with improvement in DAS-28 scores from the 1 st to the 2 nd evaluation (p = 0.041). Improvement was

Discussion
RA and MS are considered diseases with shared characteristics that may increase the risk of cardiovascular diseases [13]. Researchers, therefore, focus their studies on the prevalence of MS in RA patients. We followed patients with RA and manifestations of MS for a period of 8 years, finding a 15% increase in the prevalence of MS, associated with parameters of disease activity, use of steroid and The study shows a wide range in the prevalence of MS in patients with RA. However, these values are consonant with the global prevalence that is estimated between 14% and 63%, justified by differences in epidemiology and methodology, such as the characteristics of the studied population, the origin of the patients, the criteria used to determine MS and the study design.
Since patients with RA have a higher prevalence of MS, management must be effective, reducing the possibility of cardiovascular diseases. In our study, we found a correlation between cholesterol and triglycerides levels and between systolic and diastolic blood pressures, which may further increase the risks of morbidity and mortality in these patients.
The correlations found and described in Table 2 are as expected, although they are weak or moderate correlations. This has most likely occurred because factors that were not evaluated may have influenced the results.
Disease activity is considered a factor that may increase the incidence of MS in patients with RA and is often mentioned in studies [21] [22] [23] [24] [25]. Among our patients, the disease activity at follow-up, based on DAS-28 [26], decreased from 3.88 ± 1.4 to 3.54 ± 1.35 and was statistically significant (p < 0.006), although it did not decrease to low activity or remission.
The main limitations of this study were the lack of a comparator group and the fact that the use of cardiovascular drugs was not evaluated.
After an 8-year follow-up, there was an increase of 15% in the number of cases with MS in this cohort of patients with established RA. Therefore, our study is consistent with the literature and shows the actual magnitude of MS in patients with established RA. It also represents the parameters in MS that vary in the population of RA patients, such as blood pressure, cholesterol and triglycerides. Consequently, it is imperative that we prevent the continuous inflammatory process and appropriately manage these parameters in order to have a better prognosis.