title: Abnormal vibration induced illusion of movement in essential tremor: evidence for abnormal muscle spindle afferent function.
abstract: OBJECTIVE
  Vibration induced illusion of movement (VIIM) is abnormal in patients with idiopathic focal dystonia, an abnormality which corrects with fatigue of the vibrated muscle. Since dystonia and essential tremor sometimes coexist in families, we investigated the perception of VIIM and the effect of fatigue on VIIM in patients with essential tremor.
  
  
  METHODS
  VIIM in 18 patients with essential tremor was compared with VIIM in 18 healthy control participants before and after volitional fatigue of the vibrated muscles.
  
  
  RESULTS
  Vibration of the immobilised biceps produced a subnormal VIIM in patients with essential tremor (12.81 degrees (SEM 2.15)) compared with healthy control subjects (28.55 degrees (1.66)). The perception increased following volitional fatigue of the vibrated arm in patients with essential tremor (16.23 degrees (2.50)) but not in healthy controls (27.55 degrees (1.66)). No difference was observed in patients with alcohol or non-alcohol responsive tremor.
  
  
  CONCLUSIONS
  The VIIM decreased with increasing age in healthy control subjects. Abnormal VIIM implies abnormal sensorimotor processing in patients with essential tremor, similar to that found in idiopathic focal dystonia, and the change of the perception with age could explain the age related onset of the disorder.
authors.affiliation: Academic Neurology Unit, Division of Genomic Medicine, University of Sheffield, Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF, UK.
authors.forename: N
authors.initials: N
authors.lastname: Frima
authors.forename: R A
authors.initials: RA
authors.lastname: Grünewald
mesh_terms: D000344:Afferent Pathways / Q000503:physiopathology; D000368:Aged; D001132:Arm / Q000502:physiology; D016022:Case-Control Studies; D020329:Essential Tremor / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007088:Illusions; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D009470:Muscle Spindles / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology; D014732:Vibration