title: Jitter analysis with concentric needle electrode in the masseter muscle for the diagnosis of generalised myasthenia gravis.
abstract: OBJECTIVE
  The purpose of our study was to show neuromuscular transmission abnormality in the masseter muscle of generalised myasthenia gravis (MG) patients and to compare motor end-plate failure of the masseter with the extensor digitorum communis (EDC) and periocular muscles.
  
  
  METHODS
  Motor end-plate function was evaluated during voluntary contraction of the masseter muscle of 20 generalised MG patients aged between 16 and 63 years, as well as 20 age-matched healthy volunteers. The mean jitter value was calculated for each group and compared. The upper limit of normal jitter was also calculated and the number of jitters exceeding this cut-off value was counted for each group for comparison. In MG patients, jitter analysis was also performed in periocular and EDC muscles along with the masseter and the number of single fibre-like potentials with abnormal jitter was counted for each muscle. All tests were performed during the same session with a concentric needle electrode (CNE).
  
  
  RESULTS
  For the masseter muscle, the mean jitter of all potential pairs was significantly higher in the patient group (24.7 ± 9.6 μs in healthy volunteers, 71.9 ± 41 μs in patients). The calculated mean jitter for the 18th highest value in healthy volunteers was 33.8 ± 5.9 μs (upper 95% confidence limit was 45.6 μs). The number of abnormal jitters (≥ 46 μs) was significantly higher in the patient group (276 out of 402 jitters) compared to healthy volunteers (10 out of 400 jitters). In the patient group, the number of single fibre-like potentials with abnormal jitter was found to be similar for the masseter, periocular and EDC muscles.
  
  
  CONCLUSIONS
  The masseter muscle has diagnostic importance in generalised MG. The ratio of high jitters to all of the calculated jitters in a particular muscle was similar for masseter, periocular and EDC muscles.
  
  
  CONCLUSIONS
  Jitter analysis of the masseter muscle during voluntary contraction is easy to perform and it was found as informative as other muscles in patients with generalised MG.
authors.affiliation: Istanbul Medical Faculty, Department of Neurology, İstanbul Üniversitesi, Istanbul, Turkey. Electronic address: elifkorhan@yahoo.com.
authors.forename: Elif Kocasoy
authors.initials: EK
authors.lastname: Orhan
authors.forename: Feza
authors.initials: F
authors.lastname: Deymeer
authors.forename: Piraye
authors.initials: P
authors.lastname: Oflazer
authors.forename: Yeşim
authors.initials: Y
authors.lastname: Parman
authors.forename: Mehmet Barış
authors.initials: MB
authors.lastname: Baslo
mesh_terms: D000328:Adult; D004566:Electrodes; D004576:Electromyography / Q000295:instrumentation* / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008406:Masseter Muscle / Q000503:physiopathology*; D008875:Middle Aged; D009045:Motor Endplate / Q000502:physiology; D009119:Muscle Contraction; D009157:Myasthenia Gravis / Q000175:diagnosis* / Q000503:physiopathology; D009339:Needles; D009801:Oculomotor Muscles / Q000503:physiopathology; D009435:Synaptic Transmission; D055815:Young Adult
keywords: Concentric needle electrode; Jitter analysis; Motor end-plate; Myasthenia gravis; Single-fibre EMG; m. Masseter