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Mechanisms of Motor Impairment in Spastic Cerebral Palsy
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- Author / Creator
- Condliffe, Elizabeth, G
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This thesis discusses the pathophysiological mechanisms underlying neuromotor impairments in people with spastic cerebral palsy (CP). Ninety percent of people with CP have spastic CP and 60% have bilateral motor impairments. The first two chapters introduce CP and review the mechanisms known to contribute to motor impairments. Three original studies (Chapters 3-5) involving 17 adults with bilateral spastic CP and 15 neurologically intact (NI) controls were designed to advance this knowledge. All three studies focus on an ankle plantarflexor, the soleus muscle, which is frequently affected in bilateral spastic CP. They are followed by a general discussion. The first chapter of this thesis provides a brief overview of the disorders grouped together as CP and of motor function in spastic CP including weakness and involuntary muscle activity. The second chapter is a novel review of mechanisms known, or theorized, to contribute to neuromotor impairments in spastic CP. Changes in the cortex, in white matter pathways and within spinal circuits are discussed. The first study demonstrates abnormalities in the descending corticospinal motor pathways using transcranial magnetic stimulation (TMS) and diffusion tractography in the adults with bilateral spastic CP. New findings of this study include: decreased amplitude in motor evoked potentials (MEPs), an association between the MEP amplitudes and maximal voluntary muscle activity within the CP group and reduced facilitation of MEP amplitudes with voluntary activity. We also confirmed previous findings (often in younger participants and/or people with unilateral CP) of: changes in the motor representation to more lateral locations, higher thresholds for activation and reduced anatomic integrity of corticospinal pathways as suggested by diffusion tractography in the adults with bilateral spastic CP. The second study demonstrates an association between reduced motor function and reduced activation of motoneuron inhibitory post-synaptic potentials (IPSPs) by sensory inputs in the adults with bilateral spastic CP. We measured the activation of IPSPs using single motor unit responses to sensory stimulation. While all NI adults had evidence of IPSP activation, almost half of the CP group lacked IPSP activation. Surface electromyography was used to quantify the depth of inhibition evoked by the sensory stimulation. In the CP group, this inhibition was correlated with reduced motor function as evaluated with the Gross Motor Functional Classification System and the Functional Mobility Scale. The last original study presented is pilot work evaluating short-interval intracortical inhibition (SICI) within the motor cortex projecting to the soleus in 7 people from each of our CP and NI groups. As SICI, a paired-pulse TMS technique, is known to depend on the intensity of the initial, conditioning, stimulus we evaluated the recruitment profile in each individual. Reductions in cortical inhibitory circuits such as SICI have been theorized to contribute to involuntary muscle activity in people with spastic CP. However, we found that the participants with bilateral spastic CP had similar U-shaped recruitment profiles of SICI to our NI control group. The final chapter provides some additional reflections on the three original studies. I provide arguments supporting the generalization of our findings involving the 17 adult individuals to the broader population of people with spastic CP. However, there are some technical limitations and those that have not been discussed previously and/or are common between two or more of our studies are discussed. The final subsection of this thesis proposes future work to further advance the study of mechanism of motor impairments in spastic CP.
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- Graduation date
- Fall 2016
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.