title: Assessment of deep tissue hyperalgesia in the groin - a method comparison of electrical vs. pressure stimulation.
abstract: BACKGROUND
  Deep pain complaints are more frequent than cutaneous in post-surgical patients, and a prevalent finding in quantitative sensory testing studies. However, the preferred assessment method - pressure algometry - is indirect and tissue unspecific, hindering advances in treatment and preventive strategies. Thus, there is a need for development of methods with direct stimulation of suspected hyperalgesic tissues to identify the peripheral origin of nociceptive input.
  
  
  METHODS
  We compared the reliability of an ultrasound-guided needle stimulation protocol of electrical detection and pain thresholds to pressure algometry, by performing identical test-retest sequences 10 days apart, in deep tissues in the groin region. Electrical stimulation was performed by five up-and-down staircase series of single impulses of 0.04 ms duration, starting from 0 mA in increments of 0.2 mA until a threshold was reached and descending until sensation was lost. Method reliability was assessed by Bland-Altman plots, descriptive statistics, coefficients of variance and intraclass correlation coefficients.
  
  
  RESULTS
  The electrical stimulation method was comparable to pressure algometry regarding 10 days test-retest repeatability, but with superior same-day reliability for electrical stimulation (P < 0.05). Between-subject variance rather than within-subject variance was the main source for test variation. There were no systematic differences in electrical thresholds across tissues and locations (P > 0.05).
  
  
  CONCLUSIONS
  The presented tissue-specific direct deep tissue electrical stimulation technique has equal or superior reliability compared with the indirect tissue-unspecific stimulation by pressure algometry. This method may facilitate advances in mechanism based preventive and treatment strategies in acute and chronic post-surgical pain states.
authors.affiliation: Section of Surgical Pathophysiology, Rigshospitalet, Copenhagen University, Copenhagen, Denmark.
authors.forename: E K
authors.initials: EK
authors.lastname: Aasvang
authors.forename: M U
authors.initials: MU
authors.lastname: Werner
authors.forename: H
authors.initials: H
authors.lastname: Kehlet
mesh_terms: D000328:Adult; D004558:Electric Stimulation / Q000379:methods*; D005240:Feasibility Studies; D006119:Groin; D064368:Healthy Volunteers; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D006930:Hyperalgesia / Q000175:diagnosis*; D008297:Male; D010147:Pain Measurement / Q000379:methods*; D017288:Pain Threshold; D010149:Postoperative Pain / Q000175:diagnosis; D011312:Pressure; D017568:Rectus Abdominis; D015203:Reproducibility of Results; D040521:Subcutaneous Tissue; D018084:Ultrasonography, Interventional; D055815:Young Adult