Neuroscience
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Determining the Functional Status of the Corticospinal Tract Within One Week of Stroke
Chapters
Summary February 22nd, 2020
This protocol is for evaluating corticospinal tract function within 1 week of stroke. It can be used to select and stratify patients in trials of interventions designed to improve upper limb motor recovery and outcomes and in clinical practice for predicting upper limb functional outcomes 3 months after stroke.
Transcript
This protocol can be used to test a patient's corticospinal tract function within days of stroke in an acute hospital setting. Corticospinal tract function is an important predictor for upper limb recovery. The results of this test are useful for setting rehabilitation goals and selecting patients for rehabilitation trials.
This protocol is part of the PREP2 algorithm which predicts upper limb outcomes after stroke. These predictions allow clinicians to personalize upper limb therapies and to manage patient expectations. Demonstrating the procedures will be Emma Monigatti and Ben Scrivener, physiotherapists, and Jim Stinear, a neuroscientist, who will play the role of the stroke patient.
To assess the patient's SAFE score, position the patient with their back fully supported and upright and their paretic arm by their side with the elbow in extension. Demonstrate shoulder abduction and ask the patient to lift their arm sideways and up toward their ear. Use the medical research counsel grades to score the shoulder abduction strength.
To score grades four or five, place a hand over the patient's arm proximal to the elbow and apply resistance. Next, place the paretic forearm in pronation with the fingers fully flexed and provide support under the wrist. Demonstrate finger extension and ask the patient to straighten their fingers.
Use the medical research counsel grades, apply resistance over the dorsum of the fingers distal to the metacarpophalangeal joints throughout the movement to score grades four or five. If three fingers have the same score, use this score. If two fingers have a lower score than the other two fingers, use the lower score.
Then add the grades for shoulder abduction and finger extension together for a SAFE score out of 10. For TMS, first remove any furniture from around the bed and move the bed away from the wall. Place the TMS unit at the head of the bed toward the side opposite the paretic limb and angle the TMS unit so that the screen could be easily observed.
Remove any clothing covering the patient's paretic arm, including any items covering the wrist to allow EMG electrode placement. Position the paretic arm on a pillow with the forearm pronated and fully supported from the elbow to the hand and palpate the paretic forearm to locate the muscle belly of the ECR muscle. Identify positions for two surface EMG electrodes over the muscle belly allowing for factors such as the position of an IV cannula or dressings and use an alcohol skin cleansing wipe to clean the skin at each electrode site.
Shave each site to remove any hair and lightly abrade the skin at both sites. Then securely apply self-adhesive disposable recording electrodes to each site. Next, locate the electrode sites for the FDI muscle and prepare the skin at the sites as just demonstrated to allow the placement of one electrode on the FDI muscle belly and one on the dorsum of the hand.
Then place the reference electrode strap around the arm just proximal to the elbow. When the electrodes have been placed, lower the bed rails and move the patient as high up the bed as possible and toward the edge of the bed on the non-paretic side. Put the bed rails back up for safety and remove the headboard from the bed if possible.
Remove any unused IV poles attached to the bed that may obstruct the coil position and raise the head of the bed as high as possible. Raise the knees if possible to prevent the patient from slipping down the bed during testing and position pillows behind the patient's back to bring the patient into an upright sitting position without the head contacting the bed. Ensure that the paretic forearm is in pronation and fully supported by a pillow from the elbow to the wrist and hold the TMS coil against the patient's head to check for adequate TMS coil access.
When the patient is in position, connect the cables between the patient and the EMG unit and check to make sure that the EGM signal is free from any electrical noise. For TMS delivery, instruct the patient to look straight ahead while keeping their head still and their eyes open. Have one person hold the coil against the patient's head on the non-paretic side with the center of the coil positioned over the primary motor cortex of the stroke affected hemisphere approximately four centimeters lateral from the vertex on the interaural line.
Orient the coil with the handle pointing backwards at an approximately 45 degree angle to the midsagittal plane to produce a posterior to anterior current in the underlying tissue and adjust the bed height for the coil holder's comfort. Have a second person monitor the patient for comfort throughout the TMS session. Begin with a stimulus intensity of 30%maximum stimulator output and increase the intensity in 10%output steps with three to five stimuli at each intensity and scalp location.
Move the coil systematically in one centimeter steps in the anterior, posterior, medial, and lateral directions to find the optimal location for producing MEPs in the recorded muscles. Small adjustments to the coil rotation may also be necessary. Continue increasing the stimulus intensity and moving the coil until MEPs are consistently observed in one or both muscles or until 100%maximum stimulator output is reached.
If a 100%maximum stimulator output is reached with no MEPs observed, ask the patient to hug a pillow to their chest with both arms to attempt to activate their paretic upper limb and increase the likelihood of eliciting a MEP. For patients with no distal upper limb activity, have the patient elevate and retract the shoulder girdle. Classify the patient as MEP positive if MEPs of any amplitude are observed with a consistent latency and response to at least five stimuli either at rest or during voluntary facilitation.
FDI latencies are typically 20 to 30 milliseconds while ECR latencies are typically 15 to 25 milliseconds. MEPs do not have to exceed a peak-to-peak amplitude of 50 microvolts. Classify a patient as MEP negative if a MEP cannot be elicited at 100%maximum stimulator output either at rest or while attempting voluntary facilitation.
This representative patient had MEPs in the paretic FDI and ECR muscles while this patient had a small MEP in the FDI muscle and no MEP in the ECR muscle. This patient did not have MEPs at a 100%maximum stimulator output while at rest or when attempting active bilateral facilitation. This patient had no MEP in the FDI muscle with an elongated tail of the stimulus artifact in the ECR muscle trace.
When this artifact is present during the latency window for either muscle, the identification of a MEP can be difficult. This patient had MEPs in both muscles that are clearly identifiable despite the electrical noise in the FDI trace while this patient had MEPs only in the ECR. If the SAFE is less than five at three days post-stroke then TMS is required and should be completed within seven days post-stroke.
The SAFE score and TMS evaluate corticospinal tract function and they can be combined in the PREP2 algorithm to predict upper limb outcomes at three months after stroke. This method allows the personalization of upper limb rehabilitation goals and the selection of patients in upper limb rehabilitation trials.
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