title: Does computed tomography-based muscle density predict muscle function and health-related quality of life in patients with idiopathic inflammatory myopathies?
abstract: OBJECTIVE
  To investigate the association of low-density (lipid-rich) muscle measured by computed tomography (CT) with skeletal muscle function and health-related quality of life in idiopathic inflammatory myopathies (IIMs).
  
  
  METHODS
  Seventeen patients and 10 healthy controls underwent CT of the midthigh to quantify high- (30-100 HU) and low-density (0-29 HU) skeletal muscle areas. Anthropometric measures, body composition, physical activity level, health-related quality of life, skeletal muscle strength, endurance, and fatigue were assessed. Patients were compared against controls. The relationship of anthropometric, body composition, and disease variables with measures of muscle function were examined using Spearman's test on the patient group. Linear regression was used to assess the age- and disease-adjusted relationship of muscle quality to physical function and muscle strength.
  
  
  RESULTS
  Patients had higher body fat percentage (P = 0.042), trunk fat mass (P = 0.042), android:gynoid fat (P = 0.033), and midthigh low-density muscle/total muscle area (P < 0.001) compared to controls. Midthigh low-density muscle/total muscle area was negatively correlated with self-reported physical function, strength, and endurance (the Short Form 36 [SF-36] health survey physical functioning [P = 0.004], manual muscle testing [P = 0.020], knee maximal voluntary isometric contraction/thigh mineral-free lean mass [P < 0.001], and the endurance step test [P < 0.001]), suggesting that muscle quality impacts function in IIM. Using multiple linear regression adjusted for age, global disease damage, and total fat mass, poor muscle quality as measured by midthigh low-density muscle/total muscle area was negatively associated with SF-36 physical functioning (P = 0.009).
  
  
  CONCLUSIONS
  Midthigh low-density muscle/total muscle area is a good predictor of muscle strength, endurance, and health-related quality of life as it pertains to physical functioning in patients with IIMs.
authors.affiliation: University of Kentucky, Lexington.
authors.forename: Laura C
authors.initials: LC
authors.lastname: Cleary
authors.affiliation: Vanderbilt University, Nashville, Tennessee.
authors.forename: Leslie J
authors.initials: LJ
authors.lastname: Crofford
authors.affiliation: University of Kentucky, Lexington.
authors.forename: Douglas
authors.initials: D
authors.lastname: Long
authors.affiliation: University of Kentucky, Lexington.
authors.forename: Richard
authors.initials: R
authors.lastname: Charnigo
authors.affiliation: University of Kentucky, Lexington.
authors.forename: Jody
authors.initials: J
authors.lastname: Clasey
authors.affiliation: University of Kentucky, Lexington.
authors.forename: Francesca
authors.initials: F
authors.lastname: Beaman
authors.affiliation: University of Kentucky, Lexington.
authors.forename: Kirk A
authors.initials: KA
authors.lastname: Jenkins
authors.affiliation: University of Kentucky, Lexington.
authors.forename: Natasha
authors.initials: N
authors.lastname: Fraser
authors.affiliation: University of Kentucky, Lexington.
authors.forename: Archana
authors.initials: A
authors.lastname: Srinivas
authors.affiliation: University of Kentucky, Lexington.
authors.forename: Nicole
authors.initials: N
authors.lastname: Dhaon
authors.affiliation: University of Kentucky, Lexington.
authors.forename: Beatriz Y
authors.initials: BY
authors.lastname: Hanaoka
mesh_terms: D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D005260:Female; D006304:Health Status; D006801:Humans; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging* / Q000502:physiology*; D009220:Myositis / Q000000981:diagnostic imaging* / Q000523:psychology; D011237:Predictive Value of Tests; D011788:Quality of Life / Q000523:psychology; D013848:Thigh / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed / Q000379:methods