title: Piriformis syndrome diagnosed by cauda equina action potentials: report of two cases.
abstract: METHODS
  Evaluation of recorded potentials from the lumbar spine after stimulation of the peroneal nerve in patients with piriformis syndrome is reported.
  
  
  OBJECTIVE
  To report a new method of diagnosis of piriformis syndrome.
  
  
  BACKGROUND
  Clinically, the Freiberg and Pace signs were used to diagnose this entity. Among imaging examinations, computed tomography and magnetic resonance imaging have been used. An electrophysiological method using H reflex has also been reported. However, the best method for diagnosis of piriformis syndrome has yet to be clearly established.
  
  
  METHODS
  After having an epidural electrode inserted into the lumbar spine, patients lay on their back. Cauda equina action potentials were recorded with the epidural electrode at L3/4 after stimulation of the peroneal nerve at the fibular head. As a control, the potentials were recorded with the hip and knee extended. Potentials were then also recorded with the hip flexed, and then with the hip flexed and internally rotated to stress the sciatic nerve by the piriformis muscle.
  
  
  RESULTS
  We observed changes in amplitudes and latencies of recorded potentials. Amplitude decreased to about 70% of the control value in one case and to 67% in the other. On the nonaffected side, however, this amplitude did not decrease below 90%. The latency was also delayed on the affected side, but not on the nonaffected side.
  
  
  CONCLUSIONS
  Recording of evoked potentials from the lumbar spine with stress to the affected leg was useful for diagnosing piriformis syndrome.
authors.affiliation: Department of Orthopaedic Surgery, Osaka City University Medical School, Osaka, Japan. hnakamura@med.Osaka-cu.ac.jp
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Nakamura
authors.forename: Masahiko
authors.initials: M
authors.lastname: Seki
authors.forename: Sadahiko
authors.initials: S
authors.lastname: Konishi
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Yamano
authors.forename: Kunio
authors.initials: K
authors.lastname: Takaoka
mesh_terms: D000200:Action Potentials; D000328:Adult; D002420:Cauda Equina / Q000503:physiopathology*; D004558:Electric Stimulation; D004568:Electrodiagnosis / Q000379:methods; D005071:Evoked Potentials; D005260:Female; D006801:Humans; D008161:Lumbosacral Region; D008297:Male; D018482:Muscle, Skeletal / Q000503:physiopathology; D009408:Nerve Compression Syndromes / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology*; D010543:Peroneal Nerve / Q000502:physiology; D011237:Predictive Value of Tests; D011930:Reaction Time; D012585:Sciatica / Q000209:etiology / Q000503:physiopathology*