title: The relation among spinal geometry on MRI, paraspinal electromyographic abnormalities, and age in persons referred for electrodiagnostic testing of low back symptoms.
abstract: METHODS
  A retrospective EMG study with blinded radiologic measurement was conducted.
  
  
  OBJECTIVE
  To determine the relation among spinal measurements on MRI, paraspinal denervation, and age in patients referred for electrodiagnostic and radiologic evaluation of low back pain.
  
  
  BACKGROUND
  Spinal pathology, including disc herniation and spinal stenosis, can cause denervation of the paraspinal muscles. Various mechanisms including direct compression, inflammation, vascular compromise, and mechanical stretch of the posterior primary ramus may play a role in denervation. The relation between the amount of denervation and the size of the spinal canal can assist in understanding the pathophysiology of back pain. Since paraspinal denervation may increase with age in asymptomatic persons, age is an important covariable.
  
  
  METHODS
  At a university hospital, 44 patients referred to undergo both electrodiagnostic evaluation and MRI for low back pain were studied. The study investigated the relation among the following: 1) axial MRI spinal measurements (canal transverse diameter, anteroposterior diameter, and area; thecal sac anteroposterior diameter and area; and the radiologist's overall impression at each level) and denervation measurements in terms of scores on the MiniPM, a quantified needle electromyographic measure of paraspinal denervation; 2) various models of multilevel spinal compression (smallest, smallest two, and average spinal levels for each measurement) and MiniPM scores; and 3) MRI spinal canal measurements and age.
  
  
  RESULTS
  Although individual MRI measurements and combinations of measurements did not relate to MiniPM scores, the radiologist's impression was significantly related. The "smallest two" levels measurement had the strongest relation (r = 0.400; P < 0.007). Age related to the MiniPM scores (P = 0.004) and radiologic impression (P = 0.031). A regression suggested that MiniPM was an independent predictor of age.
  
  
  CONCLUSIONS
  The radiologist's overall impression is more accurate than axial image measurements in predicting paraspinal denervation. A combination score of the smallest two levels is the most accurate, perhaps relating to the vascular pathophysiology of stenosis. There is more denervation with increasing age in this symptomatic population.
authors.affiliation: Department of Physical Medicine and Rehabilitation, University of Michigan, Ann Arbor, Michigan 48108, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Haig
authors.forename: Justin B
authors.initials: JB
authors.lastname: Weiner
authors.forename: Joshua
authors.initials: J
authors.lastname: Tew
authors.forename: Douglas
authors.initials: D
authors.lastname: Quint
authors.forename: Karen
authors.initials: K
authors.lastname: Yamakawa
mesh_terms: D000367:Age Factors; D004568:Electrodiagnosis; D004576:Electromyography; D005260:Female; D006801:Humans; D017116:Low Back Pain / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology; D012189:Retrospective Studies; D012737:Sex Factors; D013115:Spinal Canal / Q000473:pathology; D013130:Spinal Stenosis / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology*; D013131:Spine / Q000473:pathology / Q000503:physiopathology*