Spastic tone, or spasticity, is an abnormal increase in muscle tone. This motor disorder causes muscles to become stiff or tight, interfering with movement and daily activities. It is characterized by its “velocity-dependent” nature, meaning resistance felt when moving a limb quickly is greater than when moved slowly.
The Neurological Origin of Spasticity
Spasticity arises from damage to the central nervous system (CNS), which includes the brain and spinal cord. This damage disrupts normal communication pathways, leading to an imbalance of signals. Specifically, there is a loss of inhibition of lower motor neuron pathways, resulting in hyperexcitable stretch reflexes and sustained involuntary muscle activation.
Numerous underlying conditions can cause this CNS damage. Common causes include stroke, which interrupts blood supply to parts of the brain, and cerebral palsy, a group of disorders resulting from damage to the developing brain, often before birth. Other conditions such as multiple sclerosis, a disease affecting the protective covering of nerve fibers, traumatic brain injury, and spinal cord injury also result in spasticity.
Key Characteristics and Symptoms
Spasticity manifests through several distinct physical signs. A primary characteristic is increased muscle stiffness and tightness, which can range from mild discomfort to severe rigidity. This stiffness becomes more pronounced when a muscle is stretched rapidly, akin to trying to push something quickly through thick mud, where resistance increases with speed.
Affected individuals may also experience exaggerated deep tendon reflexes, known as hyperreflexia, where a light tap on a tendon can elicit an overactive muscle contraction. Involuntary muscle spasms, which are sudden and uncontrolled muscle contractions, are common. Another specific symptom is clonus, characterized by a series of rapid, rhythmic muscle contractions and relaxations, most often observed in the ankle or knee. These symptoms can interfere with routine tasks and basic hygiene.
How Spasticity Is Diagnosed
The diagnosis of spasticity primarily relies on a thorough clinical assessment. During a physical examination, the doctor will passively move the patient’s limbs at varying speeds and through their range of motion. This maneuver helps evaluate the degree of muscle resistance and confirm the velocity-dependent nature of the increased tone. The presence of exaggerated deep tendon reflexes and clonus is also noted.
A standardized tool used to grade the severity of spastic tone is the Modified Ashworth Scale (MAS). This scale assigns a score from 0 to 4, with 0 indicating no increase in muscle tone and 4 representing a limb that is rigid in flexion or extension. An additional category, 1+, indicates a slight increase in tone with minimal resistance through less than half the range of motion. While imaging or blood tests may identify the underlying cause of CNS damage, the diagnosis of spasticity itself is largely determined by these hands-on clinical findings.
Therapeutic and Medical Interventions
Managing spasticity involves a combination of strategies. Rehabilitative therapies play a foundational role in reducing discomfort and improving function. Physical therapy incorporates stretching exercises and range-of-motion activities to maintain muscle length and joint flexibility, helping prevent fixed deformities. Occupational therapy focuses on improving daily living skills, often by teaching adaptive techniques and recommending splints or braces to support limbs and maintain proper alignment.
Medical treatments reduce muscle tone. Oral medications like baclofen, tizanidine, and dantrolene relax muscles by acting on the nervous system, though side effects like sedation can limit effectiveness. Targeted botulinum toxin (Botox) injections are used for specific muscle groups, temporarily weakening overactive muscles for several months. For severe, widespread spasticity, Intrathecal Baclofen (ITB) pump therapy may be considered. This involves surgically implanting a device to deliver baclofen directly into the fluid surrounding the spinal cord, providing more localized and potent relief.
Surgical options may be explored for spasticity that does not respond to other treatments. Selective dorsal rhizotomy (SDR) is a neurosurgical procedure that selectively cuts some sensory nerve rootlets in the spinal cord to reduce excessive muscle signals, primarily used in specific cases of spastic cerebral palsy. Orthopedic surgeries may also correct fixed joint deformities or contractures that develop as a long-term consequence of sustained spasticity. The aim of all these interventions is to reduce muscle stiffness, alleviate pain, and ultimately enhance the individual’s ability to participate in daily activities and improve their overall quality of life.