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

Mervi Könönen,Laura Säisänen,Nils Danner,Elisa Kallioniemi,Ville Leinonen,Petro Julkunen,Jani Sirkka

doi:10.1186/s12987-020-0167-0

Abstract

BackgroundIdiopathic 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.MethodsTwenty 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.ResultsAt 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).ConclusionsShorter 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.

Highlights

Idiopathic normal pressure hydrocephalus is a neurodegenerative disease with an unknown etiology
Twenty patients were evaluated for the study, two of which were excluded (LP could not be performed, n = 1, and the symptoms were regarded as too mild to pursue with invasive testing, n = 1) after the baseline measurement (Fig. 1)
At baseline (Table 3), the resting motor threshold (RMT) of upper and lower limbs were significantly lower in the Idiopathic normal pressure hydrocephalus (iNPH) patients as compared with the control group

Summary

Introduction

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. Idiopathic normal pressure hydrocephalus (iNPH) is a neurodegenerative disease with prevalence increasing with age [1, 2]. Sirkka et al Fluids Barriers CNS (2020) 17:6 benefit This emphasizes the need to identify biomarkers for shunt surgery responders in iNPH [4, 5]. Previous studies have shown that the corticospinal tract functions normally but the functional connectivity of central movement-regulating mechanisms may be disturbed [9,10,11]

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