Effect of Lumbar Drainage on Cortical Excitability in Normal Pressure Hydrocephalus

Idiopathic normal pressure hydrocephalus (iNPH) is characterized by the clinical triad of gait disturbance, urinary incontinence, and memory impairment with normal cerebrospinal fluid (CSF) pressure. Transcranial magnetic stimulation (TMS) has been used to assess the corticospinal motor pathways in patients with iNPH with conflicting results.

Our study included 11 patients with iNPH and 13 healthy controls. All the subjects underwent TMS and resting motor threshold (RMT), central motor conduction time (CMCT), short-interval intracortical inhibition (SICI), intracortical facilitation, and silent period (SP) were recorded in the upper limb. Besides, RMT and CMCT in lower limb were also recorded. Cognitive assessments were done using mini-mental status examination, Montreal cognitive assessment (MoCA), and Addenbrooke's cognitive evaluation III (ACE III). Same parameters were recorded 24 h of CSF (lumbar puncture, LP) drainage.

Mean age of the iNPH patients was 69.00 ± 6.71 years with age at onset being 66.64 ± 7.10 years. Duration of disease was 1.80 ± 1.25 years. A significant difference was noted in CMCT for the lower limb (CMCT-LL), SICI, and ipsilateral SP between pre-LP NPH and controls. Also, there was a significant difference in MoCA and ACE III between pre-LP NPH and controls. A significant reduction was observed in lower limb RMT between pre- and post-LP NPH patients. Post LP, there was a reduction in the lower limb CMCT and improvement in SICI.

A significant prolongation of CMCT-LL was observed in NPH patients. Lumbar CSF drainage in them resulted in a significant reduction in lower limb RMT thereby suggesting an increase in cortical excitability.