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Fluids Barriers CNS. 2020 Feb 17;17(1):6. doi: 10.1186/s12987-020-0167-0.

Corticospinal excitability in idiopathic normal pressure hydrocephalus: a transcranial magnetic stimulation study.

Author information

1
Neurocenter, Neurosurgery, Kuopio University Hospital and University of Eastern Finland, Kuopio, Finland. Janisir@uef.fi.
2
Department of Clinical Neurophysiology, Kuopio University Hospital, Kuopio, Finland.
3
Department of Applied Physics, University of Eastern Finland, Kuopio, Finland.
4
Department of Clinical Radiology, Kuopio University Hospital, Kuopio, Finland.
5
Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, USA.
6
Neurocenter, Neurosurgery, Kuopio University Hospital and University of Eastern Finland, Kuopio, Finland.
7
Unit of Clinical Neuroscience, Neurosurgery, University of Oulu and Medical Research Center Oulu, Oulu University Hospital, Oulu, Finland.

Abstract

BACKGROUND:

Idiopathic normal pressure hydrocephalus (iNPH) is a neurodegenerative disease with an unknown etiology. Disturbed corticospinal inhibition of the motor cortex has been reported in iNPH and can be evaluated in a noninvasive and painless manner using navigated transcranial magnetic stimulation (nTMS). This is the first study to characterize the immediate impact of cerebrospinal fluid (CSF) drainage on corticospinal excitability.

METHODS:

Twenty patients with possible or probable iNPH (16 women and 4 men, mean age 74.4 years, range 67-84 years), presenting the classical symptom triad and radiological findings, were evaluated with motor function tests (10-m walk test, Grooved Pegboard and Box & Block test) and nTMS (silent period, SP, resting motor threshold, RMT and input-output curve, IO-curve). Evaluations were performed at baseline and repeated immediately after CSF drainage via lumbar puncture.

RESULTS:

At baseline, iNPH patients presented shorter SPs (p < 0.001) and lower RMTs (p < 0.001) as compared to normative values. Positive correlation was detected between SP duration and Box & Block test (rho = 0.64, p = 0.002) in iNPH patients. CSF drainage led to an enhancement in gait velocity (p = 0.002) and a steeper IO-curve slope (p = 0.049).

CONCLUSIONS:

Shorter SPs and lower RMTs in iNPH suggest impaired corticospinal inhibition and corticospinal hyperexcitability. The steeper IO-slope in patients who improve their gait velocity after CSF drainage may indicate a higher recovery potential. Corticospinal excitability correlated with the motor function of the upper limbs implying that the disturbance in motor performance in iNPH extends beyond the classically reported gait impairment.

KEYWORDS:

Corticospinal excitability; Idiopathic normal pressure hydrocephalus; Inhibition; Lumbar puncture; Navigated transcranial magnetic stimulation

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