Repetitive Transcranial Magnetic Stimulation for Post-Stroke Visual Field Defects

Summary

Participation Requirements

Description

Visual functions are widely distributed over large areas within the cerebrum. Secondary to such wide distribution, visual field defects (VFD) are a common outcome of brain insults especially cerebrovascular stroke whether hemorrhagic or ischemic. Among these, homonymous hemianopia is the most freque...

Visual functions are widely distributed over large areas within the cerebrum. Secondary to such wide distribution, visual field defects (VFD) are a common outcome of brain insults especially cerebrovascular stroke whether hemorrhagic or ischemic. Among these, homonymous hemianopia is the most frequently encountered VFD in clinical practice. VFD ranges from 8.3% to 16% in the chronic stage of stroke, while it reaches 25% in acute and subacute stages of stroke. In other studies, it was reported to be even higher. In a database of 11900 stoke patients, VFD was found in 60.5% with homonymous hemianopia accounting for 35%. These VFDs usually show some degree of improvement within few months from onset secondary to resolution of edema and diaschisis, yet by 3 to 6 months the condition tends to become stationary with no further improvement and only 5% of patients will show full recovery of their visual field. In some studies recovery was mostly along the first 10 days of insult followed by decrease in recovery rate that nearly stops 10-12 weeks after insult. Beyond this time point, very few cases develop spontaneous recovery. Plasticity occurs in areas of residual vision (ARV) at the visual field borders rather than areas of absolute blindness. These ARVs are the functional counterpart of partially damaged brain regions at the perilesional areas. Recovery of function - both early in life and in adults - is stimulation dependent. This stimulation can be either through visual experience, behavioral training or brain stimulation. To the investigator's knowledge, direct current stimulation (DCS) is the only brain stimulation modality that has been studied in cases of VFDs. Results showed that DCS can expand visual field in stroke patients with the effects being stable over time. In the current study, it is hypothesized that stimulation of the perilesional seemingly healthy brain tissue close to the visual cortex would result in clinical improvement based on the concept of ARVs. To achieve this precise targeting, navigated rTMS would be the most suitable technique. The investigators aim to study the effect of navigated repetitive transcranial magnetic stimulation (rTMS) applied to perilesional areas on patients with cortical visual field defects (cVFD) due to stroke. This is a randomized sham-controlled clinical trial that will be conducted in the neuromodulation research lab, neurology department, Ain Shams University. The study is approved by Ain Shams University faculty of medicine local research ethics committee (REC). Procedures: 3D MRI: An MRI Brain T1WI with 200 cuts of 0.9 mm sections will be obtained. Segmentation of the head model will be done to separate scalp, skull and brain layers. A three-dimensional virtual head model will then be created for each patient. Target Selection: The target for stimulation will be determined and marked for each patient using a neuronavigation system on his virtual head model. Targets will be selected along the perilesional area in the nearest seemingly healthy tissue to the visual cortex based on the following steps: ARV (grey zone) will be identified in the perimetry of the patient. Corresponding area in the 3D head model will then be determined based on visuotopy of the primary visual cortex.

Tracking Information