Overweight patients with rheumatoid arthritis (RA) have more disease activity, lower rates of remission, and twice as likely to require a tumor necrosis factor inhibitor. Provided that the prevalence of obesity is increasing, this may significantly affect RA incidence. An association between obesity and RA is logic, as biologic mechanisms of inflammation are present in fatty tissue, and it may be a trigger to chronic systemic inflammation. Human obesity is characterized by increased plasma leptin levels, which if elevated in morbidly obese patients may enhance constitutive immunological stimuli and increased levels of inflammatory marker.
The aim of this study was to assess the impact of obesity and serum leptin level on disease activity and functional outcome in RA patients.
Patients and methods
This study was carried out at Minia University Hospital, Egypt. Patients were recruited from Rheumatology Outpatient Clinic from October 2012 to June 2013. It included 36 RA patients, fulfilling the 2010 ACR/EULAR classification criteria. They were divided into two groups: obese patients with a BMI of 25 or greater and nonobese patients (BMI ≤ 25). A total of 12 healthy individuals were included as controls. All patients were subjected to history taking and clinical examination; patient’s functional status and disease activity were assessed using the Health Assessment Questionnaire (HAQ) disability index and DAS-28, respectively. Erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and rheumatoid factor (RF) were determined. Serum level of leptin was measured using enzyme-linked immunosorbent assay. Data were analyzed using SPSS for Windows, version 16.0.
RA obese patients showed a higher duration of morning stiffness (P = 0.02), HAQ index (P = 0.001), DAS-28 (P = 0.0001), visual analogue scale (VAS) of pain (P = 0.0001), and articular index (P = 0.001) compared with nonobese ones. They showed higher ESR (P = 0.003), serum leptin (P = 0.008), CRP (P = 0.0001), and RF (P = 0.002). There was a positive correlation between BMI and each of ESR (P = 0.003), CRP (P = 0.0001), and RF (P = 0.01). There was a positive correlation between waist circumference and each of ESR (P = 0.03), serum leptin (P = 0.03), CRP (P = 0.0001), and RF (P = 0.04). There was a positive correlation between BMI and HAQ index (P = 0.0001), DAS-28 (P = 0.001), articular index (P = 0.003), and VAS of pain (P = 0.0001). There was a positive correlation between waist circumference and HAQ index (P = 0.001), DAS-28 (P = 0.03), and VAS of pain (P = 0.0001). Moreover, there was a positive correlation between VAS of pain and serum leptin (P = 0.04). Serum leptin was correlated with CRP (P= 0.01). Linear regression analysis showed that the VAS was the first and most significant risk factor (β = 0.73; P = 0.01) and that HAQ was the second (β = –0.53; P = 0.04) to affect serum leptin levels.
Obese RA patients had higher disease activity parameters, clinical scores and laboratory indices, and worse functional outcomes compared with nonobese patients. Higher serum leptin levels were associated with higher disease activity scores.