Spasticity is one of several clinical features/motor behaviors that may result following damage to the part of the brain or spinal cord involved in controlling voluntary movement. Collectively, these features are known as the upper motor neuron syndrome. Spasticity is associated with a pathologically increased muscle tone. This creates stiffness and resistance to passive movement. This change in muscle tone may increase the disability related to the disease at the origin of spasticity.
MUSCLE TONE AND STRETCH REFLEX
Muscle tone is a state of tension that is maintained continuously, minimally even when relaxed, and which increases in resistance to passive stretch. It helps to maintain posture and decreases during sleep.
The stretch reflex is a muscle contraction in response to stretching within the muscle. This reflex, by definition extremely fast, exists to allow the muscle to adapt to any kind of muscular tone and change to avoid over-stretching.
In spasticity, the muscle tone is abnormally increased (muscle hypertonia) and reflexes, such as the stretch reflex, may persist for too long and may be too strong (hyperactive reflexes). These phenomena cause an increased resistance to passive movement (e.g., if someone else tries to move the extremities of the person affected) characterized in the following ways:
- it intensifies with increasing speed of stretch and varies with the direction of joint movement and/or
- it increases above a patient-specific threshold speed or joint angle
The slower the speed and the smaller the angle when spasticity appears, the more severe the spasticity is.
How many people are affected by spasticity?
Overall, it is estimated that spasticity affects about 500.000 people in the United States and more than 12 million people throughout the world. 1
- 38% of stroke survivors experience spasticity within one year after a first stroke, while the overall prevalence (number of persons living with post stroke spasticity amongst the total population) of post-stroke spasticity is approximately 0,2% 2,3
- Around 84% of patients with multiple sclerosis have some form of spasticity and 34% have spasticity that affects their daily living 4
- It is estimated that cerebral palsy affects 2 to 4 out of every 1.000 children between 3 and 10 years of age worldwide 5
- 62% of patients with spinal cord injury are reported to have spasticity 6