title: Effect of amplifier gain setting on distal motor latency in normal subjects and CTS patients.
abstract: OBJECTIVE
  To determine normative cutoffs and sensitivities for median distal latency (MDL), median-thenar to ulnar-thenar latency difference (TTLD), and median-thenar to ulnar-hypothenar latency difference (THLD) at various amplifier gains for carpal tunnel syndrome (CTS) electrodiagnosis. A prior study utilized only an amplifier gain of 0.2 mV/division.
  
  
  METHODS
  Abnormal cutoffs for MDL, TTLD and THLD were determined based on 34 control hands at gains of 0.2, 0.5, 1, 2, and 5 mV. Diagnostic sensitivities were determined for 50 patients (80 hands) with clinically and electrodiagnostically defined CTS.
  
  
  RESULTS
  At a gain of 0.2 and 0.5 mV/division, abnormal cutoffs for MDL, THLD, and TTLD were: 3.7, 1.2, and 0.8 ms. At gains of 1, 2, and 5 mV the abnormal cutoffs were 4, 1.2, and 1 ms. The sensitivities at gains of 0.2, 0.5, 1, 2, and 5 mV for MDL, THLD, and TTLD were: 65, 66, 53, 57, 61/86, 83, 88, 86, 86/91, 91, 76, 73, 59.
  
  
  CONCLUSIONS
  MDL and THLD sensitivities are gain-independent. THLD is substantially more sensitive than MDL at all gains. TTLD sensitivity is maximized with 0.2 and 0.5 mV gains.
  
  
  CONCLUSIONS
  TTLD and THLD increase diagnostic sensitivity with minimal additional effort. TTLD sensitivity is maximized with 0.2 or 0.5 mV gains. The electromyographer's preferred gain may be used.
authors.affiliation: Department of Neurology and Neuroscience, Peripheral Neuropathy Center, Weill Medical College of Cornell University, 635 Madison Avenue, Suite 400, New York, NY 10022, USA.
authors.forename: Adina R
authors.initials: AR
authors.lastname: Goldfarb
authors.forename: Peter B
authors.initials: PB
authors.lastname: Saadeh
authors.forename: Howard W
authors.initials: HW
authors.lastname: Sander
mesh_terms: D000328:Adult; D000368:Aged; D000669:Amplifiers, Electronic / Q000592:standards; D002349:Carpal Tunnel Syndrome / Q000175:diagnosis* / Q000503:physiopathology; D004568:Electrodiagnosis / Q000295:instrumentation* / Q000379:methods*; D004576:Electromyography / Q000295:instrumentation / Q000379:methods; D006225:Hand / Q000294:innervation / Q000503:physiopathology; D006801:Humans; D008475:Median Nerve / Q000503:physiopathology*; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology; D009431:Neural Conduction / Q000502:physiology*; D011826:Radial Nerve / Q000502:physiology; D011930:Reaction Time / Q000502:physiology*; D012016:Reference Values; D014459:Ulnar Nerve / Q000502:physiology