title: Motor cortex disinhibition in normal-pressure hydrocephalus.
abstract: OBJECTIVE
  Previous studies have shown a close association between frontal lobe dysfunction and gait disturbance in idiopathic normal-pressure hydrocephalus (iNPH). A possible mechanism linking these impairments could be a modulation of corticospinal excitability. The aim of this study was 2-fold: 1) to determine whether iNPH affects corticospinal excitability; and 2) to evaluate changes in corticospinal excitability following ventricular shunt placement in relation to clinical outcome.
  
  
  METHODS
  Twenty-three patients with iNPH were examined using single- and paired-pulse transcranial magnetic stimulation of the leg motor area before and 1 month after ventricular shunt surgery. The parameters of corticospinal excitability assessed were the resting motor threshold (rMT), motor evoked potential/M-wave area ratio, central motor conduction time, intracortical facilitation, and short intracortical inhibition (SICI). The results were compared with those obtained in 8 age-matched, healthy volunteers, 19 younger healthy volunteers, and 9 age-matched patients with peripheral neuropathy.
  
  
  RESULTS
  Significant reduction of the SICI associated with a decrease of the rMT was observed in patients with iNPH at baseline evaluation. Ventricular shunt placement resulted in significant enhancement of the SICI and increase of the rMT in patients who markedly improved, but not in those who failed to improve.
  
  
  CONCLUSIONS
  This study demonstrates that iNPH affects corticospinal excitability, causing disinhibition of the motor cortex. Recovery of corticospinal excitability following ventricular shunt placement is correlated with clinical improvement. These findings support the view that reduced control of motor output, rather than impairment of central motor conduction, is responsible for gait disturbances in patients with iNPH.
authors: Department of Neurosurgery, Rambam Health Care Campus, and B. Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel. a_chistyakov@rambam.health.gov.il
authors: Andrei V
authors: AV
authors: Chistyakov
authors: Hava
authors: H
authors: Hafner
authors: Alon
authors: A
authors: Sinai
authors: Boris
authors: B
authors: Kaplan
authors: Menashe
authors: M
authors: Zaaroor
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002557:Cerebrospinal Fluid Shunts; D004525:Efferent Pathways / Q000503:physiopathology; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D020233:Gait Disorders, Neurologic / Q000209:etiology / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D006850:Hydrocephalus, Normal Pressure / Q000150:complications / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology*; D009433:Neural Inhibition / Q000502:physiology*; D011712:Pyramidal Tracts / Q000503:physiopathology; D020127:Recovery of Function; D050781:Transcranial Magnetic Stimulation; D016896:Treatment Outcome