title: Median sensory nonresponders in carpal tunnel syndrome workup.
abstract: OBJECTIVE
  To determine an optimal strategy when, in the course of performing the Combined Sensory Index (CSI) or routine median sensory evaluation of carpal tunnel syndrome (CTS), an unobtainable median sensory response is encountered.
  
  
  METHODS
  Prospectively assessed collected data for optimal electrodiagnostic strategies in the setting of an absent median sensory response.
  
  
  METHODS
  Electrodiagnostic laboratory of a Veterans Affairs medical center.
  
  
  METHODS
  Two hundred forty consecutive outpatient veterans referred to the laboratory with CTS-compatible symptoms were evaluated with the CSI. Of these, 62 were identified as having 1 or more unobtainable median CSI components.
  
  
  METHODS
  Performed tests to determine latencies across the palm and to the thumb and the ring finger; motor comparison studies of median thenar and ulnar hypothenar motor latencies and second lumbrical-interosseous latency differences.
  
  
  METHODS
  Prevalence of latency test absence, prevalence of electrophysiologically confirmed CTS, and CSI component response rate.
  
  
  RESULTS
  When the transpalmar response was absent, subsequent median-ulnar to digit 4 testing and median-radial to digit 1 testing yielded responses in 6% and 8% of cases, respectively. When the median-ulnar to digit 4 response was absent, subsequent transpalmar and median-radial to digit 1 testing yielded responses in 39% and 32% of cases, respectively. The second lumbrical-interosseous comparison was always obtainable and the standard median thenar response was obtainable in 95% of cases; the motor comparison studies confirmed a median mononeuropathy in 98% and 85% of the cases, respectively.
  
  
  CONCLUSIONS
  When initially a median CSI component is absent, subsequent median sensory studies are often unobtainable. Proceeding directly to motor comparison studies is efficient and provides the requisite electrodiagnostic information.
authors.affiliation: Physical Medicine and Rehabilitation Service, Portland Veterans Affairs Medical Center, OR 97207, USA.
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Kaul
authors.forename: Keith J
authors.initials: KJ
authors.lastname: Pagel
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002349:Carpal Tunnel Syndrome / Q000175:diagnosis* / Q000503:physiopathology*; D004568:Electrodiagnosis / Q000379:methods*; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000503:physiopathology*; D008875:Middle Aged; D009431:Neural Conduction