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Psychology

Cognitive and Behavioural Outcomes Following Paediatric Stroke

Dr Westmacott

Dr. Westmacott's research activities are focused on the types of cognitive and behavioural problems experienced by children following stroke.

Objectives:

1. To characterize the types of cognitive and behaviour problems experienced by children with stroke and to estimate their prevalence.

2. To determine risk factors for poor cognitive-behavioural outcome

3. To examine interactions between stroke location, age at stroke, and specific cognitive-behavioural outcomes.

Background:  

Arterial ischemic stroke (AIS) is a frequent cause of neurological disability in Canadian children and incidence is increasing1-3, yet it is rarely detrimental to psychological well-being, social interaction and functional independence7.   Yet, relatively little is known regarding clinical outcome in relation to stroke location, lesion size, and age at stroke8-13.  Large-scale studies suggest that neurological deficits or epilepsy are present in more than half of children with stroke before the age of 18 years and that large lesions are typically associated with poor outcome 8,9,14,15.  However, we have not yet identified reliable predictors that would allow us to prognosticate about individual children, particularly with respect to cognitive outcome 14,16.

Studies examining global measures of intellectual function (IQ) have found that, on average, scores are compromised relative to controls, but still within the average range, following both neonatal stroke (onset < 28 days) and childhood stroke (onset between 1 month and 18 years) 17-21.  However, there is a lot of unexplained variability (both between subjects and also within subjects on the subtests that make up the overall IQ index) in these studies, which limits the clinical usefulness of these findings.  For example, although side of lesion (right vs. left hemisphere) is a strong predictor of cognitive deficit patterns in adults with stroke22-24, this has not been the case with the pediatric stroke population.  Lateralized cognitive deficits are rarely seen following neonatal stroke and have been found inconsistently following childhood stroke, with a trend toward increasing lateralization with older age at stroke 12,21,25,26.  Furthermore, with respect to age at stroke and overall intellectual outcome, some studies have found evidence of a U-shaped relationship, with better outcome in neonatal stroke and stroke after the age of 5-6 years27-30.  However, other studies have failed to find a significant effect of age at stroke31-34.

Clearly, there are many unanswered questions with respect to long-term cognitive outcome in pediatric stroke.  One likely reason for equivocal findings in studies to date is that the predictor variables have not been sufficiently sensitive or specific.  Grouping children according to hemisphere of lesion, or even vascular territory, may lack the precision necessary to detect associations with intellectual and academic outcome, and more subtle cognitive difficulties in attention, memory and executive function.  Moreover, reliance on global measures, such as IQ scores, may result in failure to detect relationships between stroke variables and cognitive outcomes.  Techniques that allow for precise characterization of infarct location and size, white matter integrity and functional alterations in complex brain networks, combined with thorough neuropsychological testing, promise to provide new insights into cognitive developmental trajectories following neonatal or childhood stroke 35-37

These inconsistent findings emphasize the need to explore the impact of pediatric stroke on more specific cognitive skills, but few such studies have been done.  Given the large population of pediatric stroke patients at The Hospital for Sick Children who undergo neuropsychological testing and the strong connections between the clinical and research aspects of the program, our group is the fortunate position of being able to address these questions. 

Methods: 

Patient Selection: 

Patients seen in Stroke Clinic at The Hospital for Sick Children (38-40) are routinely referred for neuropsychological assessment.  Children presenting with cognitive or behavioural problems are given priority in terms of scheduling, but all willing patients and families are given the opportunity to participate in neuropsychological assessment.  The inclusion of patients without presenting concerns allows us to explore the frequency with which cognitive/behaviour deficits arise in this population, and associated risk factors.  Moreover, often times neuropsychological assessment is capable of picking up subtle difficulties at an early stage – before they are apparent to teachers and parents.  Many of these children are assessed longitudinally on multiple occasions, allowing us to examine development over time.  With informed consent from parents/guardians, test scores and other data gathered during the assessment are included in our research database.

Neuropsychological Assessment Protocol: 

There are three different test batteries, depending on the age of the child:  4-5 years old, 6-16 years old, or 17 years and older.  These groupings correspond to the age range of norms for each test.  We attempt to collect data on this core set of tests for all children, though it is sometimes necessary to omit tests due to poor attention or add tests in order to address a particular clinical concern. 

In addition to the index scores provided through the Wechsler Intelligence Scales, index scores will also be calculated by averaging the scores from tests within the following domains:  language expression, language comprehension, literacy skills, math skills, verbal learning and memory, visual learning and memory, attention, working memory, processing speed, executive function, visual-spatial skills, visuomotor skills, and fine-motor skills.

Quantification of lesion volumes to predict clinical outcome:

Grouping children according to hemisphere of lesion or vascular territory is not sufficiently precise to uncover associations with different aspects of language ability. Volumetric MRI allows for precise quantification of tissue volumes (and, thus, infarct size), which can be correlated with behavioural measures.  This technique has been useful in documenting structure-function relationships in a range of clinical populations that were not detectable through less sensitive methods of analysis41-47

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