Hemiparesis

Hemiparesis (from Greek hemi- — half and paresis — weakness, relaxation) is a neurological syndrome characterized by partial loss of muscle strength and restriction of voluntary movements in the arm and leg on one side of the body.

Etiology and pathophysiology

Motor commands for our muscles originate in the motor cortex of the brain. From there, nerve impulses travel down a powerful bundle of fibers (corticospinal tract). The main anatomical peculiarity of the system lies in the fact that at the junction of the brain and spinal cord, the majority of these fibers cross over to the opposite side of the body.

If, as a result of severe brain contusion or pressure from a large hematoma, the motor center is damaged or the conductive pathways in the left hemisphere are compressed, muscle weakness (paresis) will inevitably develop in the right arm and right leg. Mechanical damage to neurons interrupts the electrical signal, and the muscles stop receiving adequate contraction commands.

Clinical significance

In the context of traumatic brain injury, the development of hemiparesis is a classic focal symptom. Its appearance is a warning sign indicating significant local damage or mass effect.

Neurologists assess the severity of muscle weakness using a specific 5-point scale, where 5 points indicate normal strength and 0 points indicate total immobility (this condition is referred to as plegia or paralysis, not paresis). Identifying the side on which the weakness develops helps the emergency doctor, even before hospital arrival, to suggest in which hemisphere the traumatic hematoma is located.