title: Amplitude Manipulation Evokes Upper Limb Freezing during Handwriting in Patients with Parkinson's Disease with Freezing of Gait.
abstract: BACKGROUND
  Recent studies show that besides freezing of gait (FOG), many people with Parkinson's disease (PD) also suffer from freezing in the upper limbs (FOUL). Up to now, it is unclear which task constraints provoke and explain upper limb freezing.
  
  
  OBJECTIVE
  To investigate whether upper limb freezing and other kinematic abnormalities during writing are provoked by (i) gradual changes in amplitude or by (ii) sustained amplitude generation in patients with and without freezing of gait.
  
  
  METHODS
  Thirty-four patients with PD, including 17 with and 17 without FOG, performed a writing task on a touch-sensitive writing tablet requiring writing at constant small and large size as well as writing at gradually increasing and decreasing size. Patients of both groups were matched for disease severity, tested while 'on' medication and compared to healthy age-matched controls.
  
  
  RESULTS
  Fifty upper limb freezing episodes were detected in 10 patients, including 8 with and 2 without FOG. The majority of the episodes occurred when participants had to write at small or gradually decreasing size. The occurrence of FOUL and the number of FOUL episodes per patient significantly correlated with the occurrence and severity of FOG. Patients with FOUL also showed a significantly smaller amplitude in the writing parts outside the freezing episodes.
  
  
  CONCLUSIONS
  Corroborating findings of gait research, the current study supports a core problem in amplitude control underlying FOUL, both in maintaining as well as in flexibly adapting the cycle size.
authors.affiliation: Neuromotor Rehabilitation Research Group, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium.
authors.forename: Elke
authors.initials: E
authors.lastname: Heremans
authors.affiliation: Neuromotor Rehabilitation Research Group, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium.
authors.forename: Evelien
authors.initials: E
authors.lastname: Nackaerts
authors.affiliation: Neuromotor Rehabilitation Research Group, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium.
authors.forename: Griet
authors.initials: G
authors.lastname: Vervoort
authors.affiliation: Center for Statistics, Hasselt University, Hasselt, Belgium.
authors.forename: Sarah
authors.initials: S
authors.lastname: Vercruysse
authors.affiliation: Neuromotor Rehabilitation Research Group, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium.
authors.forename: Sanne
authors.initials: S
authors.lastname: Broeder
authors.affiliation: Neuromotor Rehabilitation Research Group, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium.
authors.forename: Carolien
authors.initials: C
authors.lastname: Strouwen
authors.affiliation: Movement Control and Neuroplasticity Research Group, Department of Kinesiology, KU Leuven, Leuven, Belgium.
authors.forename: Stephan P
authors.initials: SP
authors.lastname: Swinnen
authors.affiliation: Neuromotor Rehabilitation Research Group, Department of Rehabilitation Sciences, KU Leuven, Leuven, Belgium.
authors.forename: Alice
authors.initials: A
authors.lastname: Nieuwboer
mesh_terms: D000368:Aged; D000381:Agraphia / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D005260:Female; D005684:Gait; D020233:Gait Disorders, Neurologic / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology*; D006236:Handwriting; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement; D010300:Parkinson Disease / Q000150:complications / Q000175:diagnosis / Q000503:physiopathology*; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D034941:Upper Extremity / Q000503:physiopathology*