From the Guidelines
Increased spasticity is primarily caused by damage to the central nervous system, particularly to the motor pathways that control muscle movement, and can be exacerbated by various factors including infections, medications, and physical factors. The most recent and highest quality study, 1, published in 2025 in the Annals of Internal Medicine, provides evidence that spasticity is a common poststroke complication characterized by abnormal velocity-dependent increases in muscle tone and exaggerated reflexes. Some key factors that can contribute to increased spasticity include:
- Infections, such as urinary tract infections
- Constipation
- Pressure sores
- Tight clothing
- Extreme temperatures
- Stress or anxiety
- Certain medications like antipsychotics, some antidepressants, and sudden withdrawal from muscle relaxants
- Physical factors such as sudden movements, poor positioning, and prolonged immobility For people with existing neurological conditions like multiple sclerosis, stroke, cerebral palsy, or spinal cord injuries, spasticity can be exacerbated during disease flare-ups or as the condition progresses. Management of spasticity typically involves addressing the underlying trigger, physical therapy, and medications such as baclofen, tizanidine, or diazepam, as supported by evidence from 1 and 1. Botulinum toxin injections are also an effective treatment option for spasticity, particularly for patients with focal spasticity, as evidenced by 1 and 1. Regular stretching, proper positioning, and maintaining a consistent medication schedule can help prevent spasticity flare-ups. It is essential to note that the evidence from 1 and 1 supports the use of botulinum toxin for patients with focal spasticity, depending on patient characteristics and preferences, and that botulinum toxin may not have a dramatically different place in therapy from oral antispasmodics based on efficacy alone. Overall, a comprehensive approach to managing spasticity, including addressing underlying triggers, physical therapy, and medications, can help improve outcomes and quality of life for individuals with spasticity, as supported by the evidence from 1, 1, 1, 1, and 1.
From the FDA Drug Label
Tizanidine’s capacity to reduce increased muscle tone associated with spasticity was demonstrated in two adequate and well controlled studies in patients with multiple sclerosis or spinal cord injury. The reduction in muscle tone was not associated with a reduction in muscle strength (a desirable outcome) but also did not lead to any consistent advantage of tizanidine treated patients on measures of activities of daily living.
The causes of increased spasticity are not directly addressed in the provided drug label. However, it is mentioned that tizanidine is used to reduce increased muscle tone associated with spasticity in patients with multiple sclerosis or spinal cord injury. Key points:
- The label discusses the treatment of spasticity, not the causes.
- Spasticity is associated with multiple sclerosis and spinal cord injury. The FDA drug label does not answer the question.
From the Research
Causes of Increased Spasticity
- Spasticity is a velocity-dependent increase in muscle tone and uncontrolled, repetitive, involuntary contractions of skeletal muscles, often resulting from central nervous system pathology such as stroke, spinal cord injury, brain injury, or multiple sclerosis 2, 3, 4, 5.
- The pathophysiology of spasticity is poorly understood, but it is thought to result from interruption of inhibitory descending spinal motor pathways, leading to overactivity of the alpha motor neuron 3.
- External factors such as constipation, urinary tract infections, or pressure ulcers can worsen existing spasticity 5.
- The muscle stretch reflex is thought to play an important role in spasticity generation 4.
Factors Contributing to Spasticity
- Upper motor neuron symptoms, such as those present in patients with central nervous system pathology, can contribute to increased spasticity 2, 3, 4, 5.
- Injury to the brain or spinal cord can lead to spasticity, as it disrupts the normal regulation of muscle tone 2, 4, 5.
- Conditions such as multiple sclerosis, cerebral palsy, and stroke can increase the risk of developing spasticity 2, 3, 4, 5.