title: Serum biomarkers of inflammation and muscle strength among women with systemic lupus erythematosus.
abstract: Muscle strength is an important determinant of physical function in women with systemic lupus erythematosus (SLE). Serum biomarkers of inflammation, including interleukin-6 (IL-6) and C-Reactive Protein (CRP), are associated with differences in muscle strength among individuals without rheumatologic disease. We examined whether serum levels of IL-6 and CRP are associated with upper and lower extremity muscle strength among adult women with SLE.
  
  
  
  One hundred thirty-six women with SLE participated in this cross-sectional study. High-sensitivity CRP was analyzed by nephelometry. IL-6 serum levels were analyzed by high sensitivity enzyme-linked immunosorbent assay. Upper and lower extremity muscle strength were assessed by grip strength and peak torque of knee extension and flexion, respectively. Regression analyses modeled associations of CRP and IL-6 with upper and lower extremity muscle strength controlling for age, SLE duration, physical activity, prednisone use, BMI, plaquenil use, and pain.
  
  
  
  Higher serum levels of IL-6 and CRP were associated with significantly weaker upper and lower extremity muscle strength even when controlling for covariates.
  
  
  
  Increased serum IL-6 and CRP are associated with clinically significant differences in upper and lower extremity muscle strength and may be useful in identifying those at risk for weakness and decreased physical function.
authors.affiliation: Department of Medicine, University of Washington, Seattle, USA. Electronic address: jsa1@uw.edu.
authors.forename: James S
authors.initials: JS
authors.lastname: Andrews
authors.affiliation: Department of Medicine, University of California San Francisco, San Francisco, USA.
authors.forename: Laura
authors.initials: L
authors.lastname: Trupin
authors.affiliation: Department of Medicine, University of Washington, Seattle, USA.
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Hough
authors.affiliation: Department of Medicine, University of California San Francisco, San Francisco, USA; Department of Medicine, San Francisco VA Medical Center, San Francisco, USA.
authors.forename: David I
authors.initials: DI
authors.lastname: Daikh
authors.affiliation: Department of Medicine, University of California San Francisco, San Francisco, USA.
authors.forename: Edward H
authors.initials: EH
authors.lastname: Yelin
authors.affiliation: Department of Medicine, University of California San Francisco, San Francisco, USA.
authors.forename: Patricia P
authors.initials: PP
authors.lastname: Katz
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D002097:C-Reactive Protein / Q000378:metabolism*; D005260:Female; D006801:Humans; D018836:Inflammation Mediators / Q000097:blood*; D015850:Interleukin-6 / Q000097:blood*; D008180:Lupus Erythematosus, Systemic / Q000097:blood / Q000188:drug therapy / Q000503:physiopathology; D008875:Middle Aged; D053580:Muscle Strength; D011239:Prednisolone / Q000008:administration & dosage
chemical_list: D015415:Biomarkers; C508600:IL6 protein, human; D018836:Inflammation Mediators; D015850:Interleukin-6; D002097:C-Reactive Protein; D011239:Prednisolone
keywords: Cytokines; Inflammation; Outcomes research; Systemic lupus erythematosus