title: Timing control of gait: a study of essential tremor patients vs. age-matched controls.
abstract: BACKGROUND
  Essential tremor (ET) is a common movement disorder characterized by kinetic, postural and intention tremors. Mounting evidence suggests an underlying dysfunction of the cerebellum or cerebellar system. While few recent studies report impairments in timing control of finger movements in ET, timing control of gait has not been examined to date. We compared timing control of gait in ET patients vs. controls, and further assessed the association of these timing impairments with tremor severity among the ET patients. One-hundred-fifty-five ET patients and 60 age-matched controls underwent a comprehensive neurological assessment and gait analysis, which included walking at a criterion step frequency (cadence) with a metronome (timing production) and walking at a criterion step frequency after the metronome was turned off (timing reproduction). Outcomes of interest for both conditions were timing accuracy (measured by cadence error) and timing precision (measured by cadence variability). We also assessed cadence and step time across conditions.
  
  
  RESULTS
  Cadence was lower in ET patients than controls (p < 0.03), whereas step time was similar for ET patients and controls. Accuracy (cadence error) and precision (cadence variability) were not different in ET patients compared with controls. Cranial tremor score was significantly associated with cadence (timing production condition, p = 0.003 and timing reproduction condition, p = 0.0001) and cadence error (timing production condition, p = 0.01). Kinetic tremor and intention tremor scores were not associated with gait measures.
  
  
  CONCLUSIONS
  ET patients do not demonstrate impairments in timing control of gait as compared with matched controls. Prior work shows that patients with cerebellar dysfunction demonstrate selective impairments in timing of discrete movements (such as finger tapping) but not continuous movements (such as circle drawing). Taken together, these results support the hypothesis that the cerebellum may be important for timing control of discrete rather than continuous movements.
authors.affiliation: Department of Rehabilitation & Regenerative Medicine (Physical Therapy), College of Physicians and Surgeons, Columbia University, New York, NY USA ; G.H. Sergievsky Center, College of Physicians and Surgeons, Columbia University, New York, NY USA ; Neurological Institute, 8th Floor, 710 West 168th Street, New York, NY 10032 USA.
authors.forename: Ashwini K
authors.initials: AK
authors.lastname: Rao
authors.affiliation: Department of Neurology, Yale School of Medicine, Yale University, New Haven, CT USA ; Department of Chronic Disease Epidemiology, Yale School of Medicine, Yale University, New Haven, CT USA ; Center for Neuroepidemiology and Clinical Neurological Research, Yale School of Medicine, Yale University, New Haven, CT USA.
authors.forename: Elan D
authors.initials: ED
authors.lastname: Louis
keywords: Cerebellum; Essential tremor; Gait; Timing control