What is the pathophysiology of contralateral hemiparesis?

From the Guidelines

Contralateral hemiparesis is primarily caused by damage to the corticospinal tract, resulting from the crossing of motor pathways in the medullary pyramids, where approximately 80-90% of motor fibers decussate to the opposite side before descending through the spinal cord. This phenomenon occurs when damage to one side of the brain causes weakness or paralysis on the opposite side of the body. The pathophysiology typically involves damage to the corticospinal tract, which carries voluntary motor signals from the motor cortex to the spinal cord. Common causes include stroke (ischemic or hemorrhagic), traumatic brain injury, brain tumors, or inflammatory conditions affecting the brain. When a lesion occurs in the left cerebral hemisphere, particularly in the motor cortex or along the descending motor pathways, it results in right-sided weakness, as seen in patients with neglect syndrome, which is a cluster of attention problems associated with slow and/or inaccurate processing of and responding to stimuli occurring contralateral to the side of the brain damage 1. Conversely, damage to the right hemisphere causes left-sided weakness. The severity of hemiparesis depends on the extent and location of the brain injury, with lesions closer to the cortex typically causing more distal limb weakness, while lesions in the internal capsule or brainstem often produce more widespread motor deficits. Understanding this crossed relationship between brain injury and motor symptoms is crucial for accurate neurological localization and diagnosis.

Some key points to consider in the pathophysiology of contralateral hemiparesis include:

• The crossing of motor pathways in the medullary pyramids, where approximately 80-90% of motor fibers decussate to the opposite side before descending through the spinal cord
• Damage to the corticospinal tract, which carries voluntary motor signals from the motor cortex to the spinal cord
• The role of neglect syndrome, which is a cluster of attention problems associated with slow and/or inaccurate processing of and responding to stimuli occurring contralateral to the side of the brain damage, as seen in patients with right (nondominant) cortical strokes 1
• The importance of accurate neurological localization and diagnosis in understanding the pathophysiology of contralateral hemiparesis.

In terms of management and rehabilitation, a multifaceted approach can be helpful, including patient education, which is often a long-term process, and the goal is to teach the patient to acknowledge the neglect (to some degree) 1.

From the Research

Pathophysiology of Contralateral Hemiparesis

The pathophysiology of contralateral hemiparesis is complex and involves damage to specific areas of the brain, resulting in weakness or paralysis of the opposite side of the body.

• Contralateral hemiparesis occurs when there is damage to the motor areas of the brain, such as the anterior cerebral artery territory, which can lead to ipsilateral hemiparesis and contralateral lower limb paresis 2.
• The motor areas of the unaffected hemisphere may be reorganized after a stroke, which is important for the rehabilitation of stroke patients 2.
• Hemiparesis post-stroke can result in significant motor control deficits, including spasticity, which requires a team approach to treatment, including physical and occupational therapy, oral medication, injections of botulinum toxin, and surgery 3.

Motor Control Deficits

Motor control deficits in contralateral hemiparesis can include:

• Spasticity, which is characterized by increased muscle tone and can interfere with function 3
• Dysmetria, which is characterized by impaired coordination and movement 4
• Ataxia, which is characterized by impaired balance and coordination 4
• Hemiparesis, which is characterized by weakness or paralysis of one side of the body 5, 4

Rehabilitation

Rehabilitation of contralateral hemiparesis requires a comprehensive approach, including:

• Physical and occupational therapy to improve motor function and reduce spasticity 3, 5
• Oral medication and injections of botulinum toxin to manage spasticity 3
• Surgery to address refractory spasticity or other motor control deficits 3
• Consideration of handedness and hemispheric lateralization to tailor neurorehabilitation interventions and promote functional independence 6