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About Spasticity

Spasticity is an abnormal increase in muscle tone caused by injury of upper motor neuron pathways regulating muscles. Spasticity may be a result of multiple sclerosis (MS), cerebral palsy (CP), stroke, traumatic brain injury, or spinal cord injury. While the exact incidence of spasticity is unknown, more than half a million people in the United States, and more than 12 million worldwide,1 are affected by spasticity.

Sensory and Stretch Receptors
Although there is no definitive cause of spasticity, it is thought to be associated with an interruption of inhibitory nerve signals along the spinal cord and brain, which causes an imbalance between inhibitory and excitatory input.

Although the pathophysiology of spasticity is not completely understood, it is most commonly defined clinically as “…a motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes (‘muscle tone’) with exaggerated tendon jerks, resulting from hyperexcitability of the stretch reflex, as one component of the upper motor neuron syndrome.” 2 The velocity-dependent nature of spasticity distinguishes it from other forms of hypertonia, such as dystonia and rigidity.3

Spasticity can have a distressing effect on function, comfort, and caregiving. Spasticity may result in musculoskeletal complications, incoordination, loss of function, pain, and permanent muscle shortening or contracture.1

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Treating spasticity may:

  • Improve gait, hygiene, activities of daily living, and ease of care
  • Decrease spasm frequency, pain, and fatigue4
  • Promote tone reduction, increased range of motion, and joint position1
  • Increase patient mobility5,6
  • Complement other treatments, such as physical therapy, occupational therapy, and speech therapy
Sensory Feedback Loop
Sensory and stretch receptors in the muscles send feedback (excitatory messages) to the upper and lower motor neurons. When the muscle is stretched, the stretch receptor signals the motor neuron to contract the muscle and resist further stretching. It is thought that descending inhibitory signals (inhibitory messages) allow muscles to be stretched without contracting. Damage to the descending inhibitory pathways either in the brain (cerebral palsy, brain injury, stroke) or along the spinal cord (spinal cord trauma, multiple sclerosis) may result in severe spasticity.