The effect of shunt surgery on corticospinal excitability in idiopathic normal pressure hydrocephalus: a transcranial magnetic stimulation study.

BACKGROUND: Idiopathic normal pressure hydrocephalus (iNPH) is a multifactorial disease presenting with a classical symptom triad of cognitive decline, gait disturbance and urinary incontinence. The symptoms can be alleviated with shunt surgery but the etiology of the symptoms remains unclear. Navigated transcranial magnetic stimulation (nTMS) was applied to characterize corticospinal excitability and cortical motor function before and after shunt surgery in order to elucidate the pathophysiology of iNPH. We also aimed to determine, whether nTMS could be applied as a predictive tool in the pre-surgical work-up of iNPH. METHODS: 24 patients with possible or probable iNPH were evaluated at baseline, after cerebrospinal fluid drainage test (TAP test) and three months after shunt surgery (follow-up). Symptom severity was evaluated on an iNPH scale and with clinical tests (walking test, Box & Block test, grooved pegboard). In the nTMS experiments, resting motor threshold (RMT), silent period (SP), input-output curve (IO-curve), repetition suppression (RS) and mapping of cortical representation areas of hand and foot muscles were assessed. RESULTS: After shunt surgery, all patients showed improved performance in gait and upper limb function. The nTMS parameters showed an increase in the RMTs (hand and foot) and the maximum value of the IO-curve increased in subject with a good surgical outcome. The improvement in gait correlated with an increase in the maximum value of the IO-curve. SP, RS and mapping remained unchanged. CONCLUSION: The excitability of the motor cortex and the corticospinal tract increased in iNPH patients after shunt surgery. A favorable clinical outcome of shunt surgery is associated with a higher ability to re-form and maintain neuronal connectivity.

Upper limb dysfunction and activities in daily living in idiopathic normal pressure hydrocephalus.

BACKGROUND: Idiopathic normal pressure hydrocephalus (iNPH) is a neurodegenerative disease with a characteristic symptom triad of gait disturbance, cognitive decline, and incontinence. Recently, also dysfunctions in upper limbs have been described in iNPH and reported to improve after shunt surgery. We aim to describe the role of upper limb motor function in the clinical assessment of iNPH patients and its influence on activities of daily living (ADL). METHODS: Seventy-five consecutive patients with probable iNPH were studied pre-operatively and at 3 and 12 months after shunt surgery. The pre-operative evaluation included lumbar drainage of cerebrospinal fluid (tap test). Motor functions were assessed in upper and lower limbs with Grooved Pegboard Test (GPT), Box & Block Test (BBT), Total Score of Gait (TSG), and balance test. ADL was assessed with Barthel's index and cognition in accordance with the Consortium to Establish a Registry for Alzheimer's Disease (CERAD). RESULTS: Patients showed improvement in all motor tests and ADL at 3 months after shunt surgery. The improvement remained stable during the 12-month post-operative follow-up. The motor function tests correlated with each other and with ADL. CONCLUSIONS: A 3-month follow-up period after shunt surgery is adequate to show improvement in motor tasks, and a positive outcome will last for at least 12 months. A shunt-responsive dysfunction of upper limb motor performance plays a major role in ADL of iNPH patients. Therefore, we suggest an evaluation of upper limb motor performance to be included in routine evaluation of iNPH patients.

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

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.