Spasticity is a commonly encountered condition that can have a devastating impact on affected patients. Lance described it as “a motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with exaggerated tendon reflexes, resulting from excitability of the stretch reflex.” It can also be defined as the constant and unwanted contractions of one or more muscle groups as a result of an injury or insult to the brain or spinal cord. The condition can be mild, with patients experiencing only minor discomfort or inconvenience, or major, with the spasticity leading to immobility and the development of contractures and pressure sores. However, clinicians must use caution when applying such descriptors of severity to muscle overactivity so as not to misrepresent their clinical impact to the patient. For example, relatively slight resistance to passive motion, evaluated as “mild” by a physician, may have a quite significant functional impact for a patient, who might describe the same phenomenon as “severe.” Even mild degrees of spasticity can impair the ability to perform basic activities of daily living, including hygiene, dressing, and toileting. In addition, spasms associated with spasticity can cause pain, interrupt sleep, negatively influence mood, and impair mobility.
Although appropriate and timely treatment is needed to obtain optimal results, there is some evidence that spasticity is undertreated. Delayed or inadequate treatment can lead to maladaptive remodeling of the affected body part, leading to shortening of muscles and contracture of tendons or soft muscle and, ultimately, to a permanent physical deformity.
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Pathologic changes in the central nervous system often create a constellation of symptoms or signs that encompass both positive and negative components. Weakness and loss of dexterity, the most commonly encountered negative phenomena, are relatively easy to define. Other negative signs include atrophy, fatigability, and loss of selective motor control. The positive components are more complex, with diverse pathophysiologic mechanisms. Observable phenomena include increased resistance to passive stretch, muscle–tendon hyperreflexia, clonus, co-contraction of synergistic muscle groups, and spontaneous flexor–extensor spasms. Spasticity is only one of these features, namely, a velocity-dependent increase in resistance to passive range of motion (ROM). Collectively, all of the positive signs can be called “muscle overactivity,” with the qualification that abnormal pathology extends beyond the muscle itself. Frequently, and perhaps unfortunately, the term spasticity is often applied to the entire collection of signs. Given this common practice, spasticity and muscle overactivity are used somewhat interchangeably for remainder of this chapter.
The causes of spasticity are heterogeneous. This syndrome is usually seen in conditions that involve damage to the portion of the brain or spinal cord ...