title: Force control deficits in individuals with Parkinson's disease, multiple systems atrophy, and progressive supranuclear palsy.
abstract: OBJECTIVE
  This study examined grip force and cognition in Parkinson's disease (PD), Parkinsonian variant of multiple system atrophy (MSAp), progressive supranuclear palsy (PSP), and healthy controls. PD is characterized by a slower rate of force increase and decrease and the production of abnormally large grip forces. Early-stage PD has difficulty with the rapid contraction and relaxation of hand muscles required for precision gripping. The first goal was to determine which features of grip force are abnormal in MSAp and PSP. The second goal was to determine whether a single variable or a combination of motor and cognitive measures would distinguish patient groups. Since PSP is more cognitively impaired relative to PD and MSAp, we expected that combining motor and cognitive measures would further distinguish PSP from PD and MSAp.
  
  
  METHODS
  We studied 44 participants: 12 PD, 12 MSAp, 8 PSP, and 12 controls. Patients were diagnosed by a movement disorders neurologist and were tested off anti-Parkinsonian medication. Participants completed a visually guided grip force task wherein force pulses were produced for 2 s, followed by 1 s of rest. We also conducted four cognitive tests.
  
  
  RESULTS
  PD, MSAp, and PSP were slower at contracting and relaxing force and produced longer pulse durations compared to controls. PSP produced additional force pulses during the task and were more cognitively impaired relative to other groups. A receiver operator characteristic analysis revealed that the combination of number of pulses and Brief Test of Attention (BTA) discriminated PSP from PD, MSAp, and controls with a high degree of sensitivity and specificity.
  
  
  CONCLUSIONS
  Slowness in contracting and relaxing force represent general features of PD, MSAp, and PSP, whereas producing additional force pulses was specific to PSP. Combining motor and cognitive measures provides a robust method for characterizing behavioral features of PSP compared to MSAp and PD.
authors.affiliation: Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, United States of America.
authors.forename: Kristina A
authors.initials: KA
authors.lastname: Neely
authors.forename: Peggy J
authors.initials: PJ
authors.lastname: Planetta
authors.forename: Janey
authors.initials: J
authors.lastname: Prodoehl
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Corcos
authors.forename: Cynthia L
authors.initials: CL
authors.lastname: Comella
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Goetz
authors.forename: Kathleen L
authors.initials: KL
authors.lastname: Shannon
authors.forename: David E
authors.initials: DE
authors.lastname: Vaillancourt
mesh_terms: D000368:Aged; D003071:Cognition; D005260:Female; D018737:Hand Strength; D006801:Humans; D008297:Male; D008875:Middle Aged; D019578:Multiple System Atrophy / Q000175:diagnosis / Q000503:physiopathology*; D010300:Parkinson Disease / Q000175:diagnosis / Q000503:physiopathology*; D012372:ROC Curve; D013494:Supranuclear Palsy, Progressive / Q000175:diagnosis / Q000503:physiopathology*