title: Amplitude fluctuations in essential tremor.
abstract: OBJECTIVE
  To assess temporal amplitude variability in patients with essential tremor (ET).
  
  
  METHODS
  Patients who satisfied the diagnostic criteria for probable or definite ET were enrolled in the study. Each enrolled patient was first rated using the essential tremor rating assessment scale (TETRAS). Postural and kinetic tremors of the arms were then measured using a quantitative motor assessment system (QMAS) starting at 8:00 AM (T0-baseline) every 2 h for 6 h. Subjects were videotaped performing the tasks. Single subjects consecutively performed each assessment twice during every time-interval. At the end of the study, videos were randomized and blindly rated using TETRAS.
  
  
  RESULTS
  Twelve ET subjects were enrolled. QMAS and video scores were directly correlated with high test-retest reliability for each time-interval. Furthermore, the QMAS scores at T0 significantly correlated with in-person rated TETRAS scores as well as with subsequent time-intervals instrumental scores. No significant differences were detected between time-intervals QMAS average measurements using ANOVA. There was a maximal 23% absolute variation in tremor amplitude from baseline as determined by the QMAS. Test for equality of variance showed high measurement variability for subjects with high QMAS scores at T0 and throughout the 6 h of assessment.
  
  
  CONCLUSIONS
  Baseline measures are predictive of tremor amplitude at subsequent assessments during the day. High amplitude tremor is associated with high intra-assessment variability.
authors.affiliation: Parkinson's Disease Center and Movement Disorders Clinic, Department of Neurology, Baylor College of Medicine, The Smith Tower, Suite 1801, 6550 Fannin, Houston, TX 77030, USA.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Mostile
authors.forename: Robert
authors.initials: R
authors.lastname: Fekete
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Giuffrida
authors.forename: Toby
authors.initials: T
authors.lastname: Yaltho
authors.forename: Anthony
authors.initials: A
authors.lastname: Davidson
authors.forename: Alessandra
authors.initials: A
authors.lastname: Nicoletti
authors.forename: Mario
authors.initials: M
authors.lastname: Zappia
authors.forename: Joseph
authors.initials: J
authors.lastname: Jankovic
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001132:Arm / Q000503:physiopathology*; D020329:Essential Tremor / Q000175:diagnosis / Q000503:physiopathology*; D006801:Humans; D008875:Middle Aged; D018670:Monitoring, Ambulatory / Q000379:methods*; D009043:Motor Activity / Q000502:physiology; D009460:Neurologic Examination; D015203:Reproducibility of Results; D014743:Videotape Recording / Q000379:methods; D055815:Young Adult