Abstract
BackgroundIn the population a high body mass index (BMI) has been associated with slightly increased inflammatory markers. Within rheumatoid arthritis (RA), however, a high BMI has been associated with less radiographic progression; this phenomenon is unexplained. We hypothesized that the phenomenon is caused by an inverse relationship between BMI and inflammation in hand and foot joints with RA. To explore this hypothesis, local inflammation was measured using magnetic resonance imaging (MRI) in early arthritis patients presenting with RA or other arthritides and in asymptomatic volunteers.MethodsA total of 195 RA patients, 159 patients with other inflammatory arthritides included in the Leiden Early Arthritis Clinic, and 193 asymptomatic volunteers underwent a unilateral contrast-enhanced 1.5 T MRI scan of metacarpophalangeal, wrist, and metatarsophalangeal joints. Each MRI scan was scored by two readers on synovitis, bone marrow edema (BME), and tenosynovitis; the sum yielded the total MRI inflammation score. Linear regression on log-transformed MRI data was used.ResultsA higher BMI was associated with higher MRI inflammation scores in arthritides other than RA (β = 1.082, p < 0.001) and in asymptomatic volunteers (β = 1.029, p = 0.040), whereas it was associated with lower MRI inflammation scores in RA (β = 0.97, p = 0.005). Evaluating the different types of inflammation, a higher BMI was associated with higher synovitis, BME, and tenosynovitis scores in arthritides other than RA (respectively β = 1.084, p < 0.001, β = 1.021, p = 0.24, and β = 1.054, p = 0.003), but with lower synovitis and BME scores in RA (respectively β = 0.98, p = 0.047 and β = 0.95, p = 0.002).ConclusionsIncreased BMI is correlated with less severe MRI-detected synovitis and BME in RA. This might explain the paradox in RA where obesity correlates with less severe radiographic progression.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-016-1146-3) contains supplementary material, which is available to authorized users.
Highlights
In the population a high body mass index (BMI) has been associated with slightly increased inflammatory markers
Because an advantageous effect of BMI has only been observed far in rheumatoid arthritis (RA), we evaluated the association between BMI and MRIdetected inflammation differed in RA patients compared with patients with other inflammatory arthritides or with asymptomatic volunteers
The following sequences were acquired: T1 fast-spin echo (T1), T2-weighted fat saturated (T2), and, after intravenous contrast administration, T1 fast-spin echo with fat saturation (T1 Gd)
Summary
In the population a high body mass index (BMI) has been associated with slightly increased inflammatory markers. To explore this hypothesis, local inflammation was measured using magnetic resonance imaging (MRI) in early arthritis patients presenting with RA or other arthritides and in asymptomatic volunteers. A population-based study has shown that a high body mass index (BMI) is associated with increased inflammatory markers, such as C-reactive protein (CRP) [1]. Several studies have observed and replicated that a higher BMI is associated with less severe radiographic joint progression in RA [3,4,5,6]. The mechanisms underlying this observation are unknown. Together these observations prompted us to study the association between BMI and MRI-detected joint inflammation in more detail
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