title: Body mass index and extent of MRI-detected inflammation: opposite effects in rheumatoid arthritis versus other arthritides and asymptomatic persons.
abstract: In 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.
  
  
  
  A 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.
  
  
  
  A 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).
  
  
  
  Increased 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.
authors: Department of Rheumatology, Leiden University Medical Center, P.O. Box 9600, Leiden, 2300 RC, The Netherlands. l.mangnus@lumc.nl.
authors: Lukas
authors: 0000-0001-6978-0680
authors: L
authors: Mangnus
authors: Department of Rheumatology, Leiden University Medical Center, P.O. Box 9600, Leiden, 2300 RC, The Netherlands.
authors: Wouter P
authors: WP
authors: Nieuwenhuis
authors: Department of Rheumatology, Leiden University Medical Center, P.O. Box 9600, Leiden, 2300 RC, The Netherlands.
authors: Hanna W
authors: HW
authors: van Steenbergen
authors: Department of Rheumatology, Leiden University Medical Center, P.O. Box 9600, Leiden, 2300 RC, The Netherlands.
authors: Tom W J
authors: TW
authors: Huizinga
authors: Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands.
authors: Monique
authors: M
authors: Reijnierse
authors: Department of Rheumatology, Leiden University Medical Center, P.O. Box 9600, Leiden, 2300 RC, The Netherlands.
authors: Annette H M
authors: AH
authors: van der Helm-van Mil
mesh_terms: D000368:Aged; D001168:Arthritis / Q000000981:diagnostic imaging / Q000473:pathology; D001172:Arthritis, Rheumatoid / Q000150:complications* / Q000000981:diagnostic imaging / Q000473:pathology*; D015992:Body Mass Index; D001853:Bone Marrow / Q000000981:diagnostic imaging / Q000473:pathology; D003430:Cross-Sectional Studies; D004487:Edema / Q000000981:diagnostic imaging / Q000473:pathology; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D007249:Inflammation / Q000000981:diagnostic imaging / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008662:Metacarpophalangeal Joint / Q000000981:diagnostic imaging / Q000473:pathology; D008683:Metatarsophalangeal Joint / Q000000981:diagnostic imaging / Q000473:pathology; D008875:Middle Aged; D009765:Obesity / Q000150:complications / Q000000981:diagnostic imaging / Q000473:pathology; D050177:Overweight / Q000150:complications* / Q000000981:diagnostic imaging / Q000473:pathology*
keywords: Asymptomatic volunteers; Body mass index; Inflammation; Magnetic resonance imaging; Rheumatoid arthritis