Spasticity

Spasticity is a motor disorder in which muscle tone increases with the speed of stretch, often causing exaggerated reflexes, stiffness, and involuntary muscle activity.

Stretch reflex: A spinal reflex in which muscle stretch activates sensory signals that trigger contraction of the same muscle. Its heightened response to stretch is a defining feature of spasticity.
Stroke: Sudden neurological injury caused by interrupted blood flow to the brain or bleeding within it. Damage to descending motor pathways can produce spasticity after a stroke.
Modified Ashworth Scale: A clinical rating scale that grades resistance encountered during passive movement of a limb. Clinicians commonly use it to document muscle tone in spasticity.
Dystonia: A movement disorder involving sustained or intermittent muscle contractions that cause abnormal movements or postures. Dystonic postures arise from patterned contractions, not simply velocity-dependent stretch resistance.
Upper motor neuron: A motor neuron pathway that carries commands from the brain or brainstem to spinal motor circuits. Damage to these pathways commonly removes control that normally restrains spinal reflex activity.
Cerebral palsy: A group of permanent disorders of movement and posture caused by early brain development injury or disruption. Spasticity is a common motor feature of cerebral palsy.
Tardieu Scale: A clinical assessment that measures muscle reaction to stretch at different speeds and joint angles. Its speed-sensitive observations align more directly with spasticity's defining physiology.
Parkinsonian rigidity: Increased resistance to passive movement associated with parkinsonism, often affecting movement throughout its range. Its resistance is generally less dependent on stretch speed than spasticity.
Gamma motor neuron: A motor neuron that adjusts the sensitivity of muscle spindle sensory receptors. Altered spindle sensitivity can contribute to increased stretch-reflex responses.
Multiple sclerosis: An immune-mediated disease in which damage to central nervous system myelin disrupts nerve signaling. Spinal cord and brain lesions can cause stiffness, spasms, and spasticity.

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