Perinatal Stroke: Understanding Brain Reorganization

Background and Significance

Perinatal stroke affects more than1 in 2,300 live births. Perinatal stroke is the most common cause of hemiparetic cerebral palsy (CP). Even with prompt behavioral therapy, ongoing significant residual motor impairments are common in these children. In this case, innovative interventions that take advantage of the early critical window for optimizing outcomes are urgently needed—in infancy. Thus, understanding the early brain reorganization before the brain has not yet largely reorganized is critical for developing efficacious early intervention.

Current pediatric studies have employed non-invasive brain stimulation, and most commonly use the single or paired-pulses of Transcranial Magnetic Stimulation (TMS) to evaluate brain plasticity by assessing cortical excitability. To date, there is only one infant study using TMS to assess cortical excitability with perinatal stroke. As a unique aspect of investigation, this study will combine Magnetic Resonance Imaging (MRI)/ Diffusion Tensor Imaging (DTI) and TMS to provide an additional opportunity to assess both the cortical excitability and corticospinal tract (CST) integrity in infants with perinatal stroke.

Identifying the association between laboratory assessment results and developmental outcomes is also critical. The General Movements Assessment (GMA) is a quick and non-invasive way to evaluate motor performance and to predict CP in high-risk infants before 20 weeks of age (corrected age for preterm infants). The BSID-III is a standardized, norm-referenced developmental assessment validated for use for children 1-42 months of age to assess motor function. Thus, the purpose of this study is to use MRI/DTI and TMS to comprehensively examine both the CST integrity and cortical excitability in infants following perinatal stroke, and to identify association with motor outcome as evaluated by movement assessment

Specific Aims/Study Objectives

Aim 1: Use TMS to index maladaptive cortical reorganization by assessing the relative excitability of corticospinal projections from each hemisphere to upper extremity musculature in 3 to 24 month old children who have a confirmed diagnosis of perinatal stroke.

Hypothesis: The ipsilesional hemisphere will have a smaller "map volume" (lower cortical excitability) than the contralesional hemisphere (larger map volume).

Aim 2: Index maladaptive cortical reorganization by evaluating the organizational integrity of the CSTs bilaterally via fractional anisotropy (FA), a standardized metric derived from DTI, in infants with perinatal stroke.

Hypothesis 1: Ipsilesional CST will have a lower value of FA than the contralesional CST.

Hypothesis 2: Smaller cortical excitability volumes will be associated with lower values of FA.

Aim 3: For infants with perinatal stroke, examine the relationship between movement quality derived from the movement assessment and cortical excitability and with CST integrity.

Hypothesis: Atypical movement assessment outcome scores will be associated with a lower FA value and lower ipsilesional CST excitability.

Aim 4: Record any feasibility issues that arise, and monitor for adverse events during TMS cortical mapping and MRI scanning of infants with perinatal stroke.

Hypothesis 1: TMS and MRI assessments of infants with perinatal stroke are feasible.

Hypothesis 2: No seizure or other serious adverse event related to TMS or MRI/DTI will occur in this study.

Additional Aims as of October 2019:

Aim 5: Evaluate relationship between legion, heterogeneity, and cortical motor excitability and circuitry

Hypothesis: The larger the lesion the higher the motor threshold and the greater the probability of atypical ipselateral CST circuitry

Aim 6: Using MRI and computational modeling to estimate individualized electric fields from each infants neuroanatomy

Hypothesis 1: The larger the lesion and motor threshold the lower the model peak electric field Hypothesis 2: There is an association between the electric field and individual neuroanatomy

Research Design and Methods

Study design and sample size: This study will be a cross-sectional, two-visit pilot study with MRI scanning on Visit 1, and TMS and movement assessment testing on the Visit 2. Thirty term or preterm infants between 3 and 24 months of age corrected for prematurity with the diagnosis of perinatal stroke will be enrolled.

Subjects Recruitment Plan:

Stage 1: For families who contact the investigators with interest in this study after seeing the recruitment letter or flyer, initial screening process will be completed. This includes review of medical records obtained by signatures on an authorization form to list the clinics to be contacted for medical records.

Stage 2: Once the investigators have determined eligibility for study criteria for the infant, they will mail the family the consent and HIPAA for review, follow-up with a phone call to discuss any questions and then schedule a consent meeting to discuss and obtain signatures. If the family deems appropriate, this can occur on the same day as Visit 1.

Procedures

Visit 1 (MRI/DTI)

Preparatory Activity:

One week prior to Visit 1, the study team will educate caregivers as to how to prepare the infant for the optimal MRI experience. Caregivers will receive a digital file with a recording of the MRI operation sound. The caregivers will be asked to play these sounds while the infant sleeps so they become familiarized with these noises.

Day of Visit:

Infants will be fed, by their caregiver in a separate calming room, and then allowed to fall asleep for MRI scanning. A memory foam mattress for infants will be used to support them firmly and comfortably on the scanner table. Both silicone infant ear plugs and ear protector will both be used to diminish the noises during scanning. One researcher will stay with the infants throughout the scanning session to ensure and monitor infants' responses and safety. Subjects will be scanned on a Siemens 3Tesla (magnet strength) system at the Center for Magnetic Resonance Research (CMRR).

The scan protocol will include both an anatomical T1-weighted structural MPRAGE scan with spatial resolution 1x1x1mm3 that will be used to guide the TMS testing in Aim 2 and DTI which will allow investigation of the variation in connectivity of the CST in these infants with perinatal stroke. High angular resolution diffusion imaging (HARDI) with whole-brain coverage using the 'Human Connectome Project' (HCP) DTI sequence and spatial resolution 1.8x1.8x1.8mm3, b-value=1500 s/mm2, 128 gradient directions and 15 additional non-diffusion weighted images will be obtained. HCP tractographic methods will be applied to the HARDI data to define the two CST's and compute the integrity metrics of track volume and mean fractional anisotropy (FA). The complete MRI dataset will be obtained in less than 38 minutes.

Visit 2 (Movement Assessment and TMS):

Visit 2 will be scheduled within 7 days after Visit 1 to avoid nonsynchronous results of MRI/DTI and TMS due to natural developmental changes of central nervous system.

Movement Assessment:

For GMA scoring, infants will be placed in supine position wearing only a diaper to allow for clear observation of trunk and limbs spontaneous movements. Infants will be observed and videotaped for 5-10 minutes in an awake but calm state without interacting with people around them or while playing with a toy. The classifications of "typical" and "atypical" of different movement categories of GMA will be determined to define the ranks of motor outcomes in each infant.

The BSID-III motor scales will be administered and scored by a pediatric physical therapist. This assessment will take approximately 30-45 minutes to complete and involves assessing a child's natural movements and interactions with toys and objects. The BSID-III is a norm-referenced assessment that allows comparison of scores to typically developing age matched peers.

TMS:

Single-pulse TMS (Bistim2, Magstim, UK) with a 50mm figure-of-eight coil (P/N4186-00,Magstim, UK) will be used to assess cortical excitability from the M1 region of both the ipsilesional and contralesional hemispheres under the guidance of a frameless stereotactic neuronavigation system (Brainsight, Rogue Research, Montreal, Quebec, Canada). Each infant's MRI will be projected onto the neuronavigation system to assist with localization of the motor cortex (T1 MPRage).

Mapping (10 minutes): A 5-by-5 cortical grid of target (25 targets in total) with the interval 1 cm (4X4 cm2) will be generated over the motor cortex area in the Neuronavigation System. A response map based on the peak-to-peak amplitude of MEP will be created in real time by a customized program (LabVIEW, v2012, National Instruments, Austin, TX) program.

Hotspot determination and motor threshold determination (15 minutes): The target with the greatest motor evoke potential (MEP) peak-to-peak amplitude will be defined as the hotspot which is the most responsive location on the motor cortex. After determining the hotspot, the motor threshold (MT) will be assessed over the hotspot. We define the resting MT as the minimal TMS output necessary to produce MEPs with a peak-to-peak amplitude >50 microvolts in at least 3 out of 5 consecutive trials. EMG signal will be recorded using surface electromyography (EMG) electrodes attached over bilateral biceps based. All data will be collected by a custom EMG amplifier and data acquisition system and stored by LabVIEW program (National Instruments, Austin, TX) for offline analysis.

Anticipated Risks/Risk Mitigation:

MRI-Dislodging of indwelling metals and disruption of medical devices: Exclude if metal/medical devices are incompatible.

MRI-Metal projectiles inadvertently presented during MRI: Conduct on-site screen and removal of potential projectiles (coins, keys, etc).

MRI-Temporary mild hearing loss due to noise level of equipment: Subjects will wear earplugs (~20 decibel reduction) and headphones (~35 dB reduction) during MRI to protect against excessive noise MRI-Discomfort due to positioning: Investigator to be present in MRI room throughout the scan with visual and tactile monitoring MRI-Wake up and move during the MRI scanning: One investigator will stay with the infants throughout the scanning process to monitor infants' arousal state and secure the infants if the infants are fully awake TMS-Stimulation over a tumor which may alter metabolic activity: Screen appropriately for exclusion criteria of neoplasm.

TMS-Threshold altering pharmacologic agent: Physician review of each medical record for determination of appropriateness for study inclusion.

TMS-Pain: Age-appropriate Vital signs (HR, RR and BP), skin integrity, distress responses will be continuously monitored for determination of pausing or stopping.

TMS-Fatigue, Sleepiness: Infant arousal state will be monitored and recorded each minute during the TMS test TMS-Temporary mild hearing loss due to noise level of equipment: Silicon infant-appropriate ear plugs will be inserted before TMS and continuously checked for placement.

TMS-Safe practices will be further ensured by establishing the location for testing within the University of Minnesota's Clinical and Translational Science Institute (CTSI), where the equipment and personnel to manage a seizure or other complications are present if an adverse event occurs, the protocol will be following and the infant will be assessed and the study reviewed for safety.

TMS-No serious adverse events have been reported from the few published studies investigating TMS in infants. As the innovation of this study is to investigate comprehensively both the safety and feasibility of TMS and neuroimaging in infant, we have devised complete individual and entire study stopping rules.

GMA-Concern for facial recognition and loss of anonymity: The recording will be destroyed after it is coded, up to 5 years after the completion of the study. This recording will not be used for any purposes outside of the research study.

(The longitudinal component described in this paragraph has been removed as of October 2019) Follow up assessments will be repeated at 12 and 24 months of age corrected for prematurity. The investigators will incorporate a follow-up phone call 1-month after participation to continue the assessment of safety. Questions pertaining to change in medical status, including any onset of seizures will be asked.