title: Imaging Psoas Sign in Lumbar Spinal Infections: Evaluation of Diagnostic Accuracy and Comparison with Established Imaging Characteristics.
abstract: OBJECTIVE
  Lumbar discitis-osteomyelitis has imaging characteristics than can overlap with noninfectious causes of back pain. Our aim was to determine the added accuracy of psoas musculature T2 hyperintensity (imaging psoas sign) in the MR imaging diagnosis of lumbar discitis-osteomyelitis.
  
  
  METHODS
  This retrospective case-control study evaluated lumbar spine MR imaging examinations, during a 30-month period, that were requested for the evaluation of discitis-osteomyelitis. Of this pool, 50 age-matched control patients were compared with 51 biopsy-proved or clinically diagnosed patients with discitis-osteomyelitis. Two reviewers, blinded to the clinical information, assessed the randomly organized MR imaging examinations for abnormalities of the psoas musculature, vertebral bodies, discs, and epidural space.
  
  
  RESULTS
  Psoas T2 hyperintensity demonstrated a high sensitivity (92.1%; 95% CI, 80%-97.4%) and specificity (92%; 95% CI, 80%-97.4%), high positive likelihood ratio (11.5; 95% CI, 4.5-29.6), low negative likelihood ratio (0.09; 95% CI, 0.03-0.20), and individual area under the receiver operating characteristic curve of 0.92; 95% CI, 0.87-0.97. Identification of psoas T2 abnormality significantly improved (P = .02) the diagnostic accuracy of discitis-osteomyelitis in noncontrast examinations from an area under the receiver operator characteristic curve of the established variables (vertebral body T2 and T1 signal, endplate integrity, disc T2 signal, and disc height) from 0.93 (95% CI, 0.88-0.98) to 0.98 (95% CI, 0.96-1.0). Psoas T2 abnormalities also had the highest interobserver reliability with a κ coefficient of 0.78 (substantial agreement).
  
  
  CONCLUSIONS
  Psoas T2 hyperintensity, the imaging psoas sign, is highly correlated with discitis-osteomyelitis. T2 hyperintensity in the psoas musculature, particularly when there is clinical suspicion of spinal infection, improves the diagnostic accuracy of discitis-osteomyelitis compared with routine noncontrast variables alone.
authors.affiliation: From the Department of Radiology (L.N.L.), University of Kansas Medical Center, Kansas City, Kansas lledbetter@kumc.edu.
authors.forename: L N
authors.identifier: http://orcid.org/0000-0003-4531-4671
authors.initials: LN
authors.lastname: Ledbetter
authors.affiliation: Department of Radiology (K.L.S., L.M.S.), University of Utah, Salt Lake City, Utah.
authors.forename: K L
authors.identifier: http://orcid.org/0000-0002-3298-6607
authors.initials: KL
authors.lastname: Salzman
authors.affiliation: Department of Radiology (K.L.S., L.M.S.), University of Utah, Salt Lake City, Utah.
authors.forename: L M
authors.identifier: http://orcid.org/0000-0003-1303-3533
authors.initials: LM
authors.lastname: Shah
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D015299:Discitis / Q000000981:diagnostic imaging; D004824:Epidural Space / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D017116:Low Back Pain / Q000000981:diagnostic imaging; D008161:Lumbosacral Region; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D010019:Osteomyelitis / Q000000981:diagnostic imaging; D016658:Psoas Muscles / Q000000981:diagnostic imaging*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013118:Spinal Cord Diseases / Q000000981:diagnostic imaging*; D013131:Spine / Q000000981:diagnostic imaging; D055815:Young Adult