Spasticity is the uncontrolled tightening or contracting of the muscles that is common in individuals with spinal cord injuries.
Spasticity, and that associated with spinal cord injury, is the uncontrolled tightening or contracting of the muscles that is common in individuals with spinal cord injuries. About 65%–78% of the SCI population have some amount of spasticity, and it is more common in cervical (neck) than thoracic (chest) and lumbar (lower back) injuries.
Symptoms and severity of spasticity vary from person to person and can include:
- Sudden, involuntary flexing (bending) or extending (straightening) of a limb, or jerking of muscle groups such as in the trunk (chest, back, and abdomen), bladder, or rectum;
- Hyperactive (overactive) reflexes, such as a muscle spasm when you are lightly touched. Stiff or tight muscles at rest, so that it is difficult to relax or stretch your muscles; and
- Muscle tightness during activity, making it difficult for you to control your movement.
Spasticity (tone) develops when there is an injury in certain parts of the nervous system. These are upper motor neurons, the spinal cord reflexes and the stretch reflex of the muscle affected. Sensory nerves send messages from the body to the brain. These messages are created from information gathered by the sensory nerves of the skin and those from within the body. The sensory nerves indicate if the body is feeling pleasure, feeling distress, or functioning well. Instantaneously, the brain will respond for the body to adjust by messages sent through motor neurons. Motor neurons receive messages from the brain to send to the body. The motor neurons will speed up or slow down activity inside the body as well as tell the body to move for adjustments in positioning and comfort. Motor neurons control muscles, internal organs, and glands. Body functions and movement are regulated by motor neurons.
There are two types of motor neurons, upper motor neurons (UMN) and lower motor neurons (LMN). Although they share the same name, motor neurons, there are more differences than similarities. UMNs originate in the brain, specifically in the motor strip section. LMNs originate in the brainstem or spinal cord. Injury to UMNs lead to spasticity (tone). Most typically, injuries to the cervical or thoracic levels of the spinal cord will result in changes to UMN functioning which results in spasticity (tone). Injuries at the lumbar or sacral areas result in LMN function changes which are flaccid muscles or limp muscles. This is often the case but there can also be mixed effects which are a result of a combination of symptoms of UMN (spasticity) and LMN (flaccidity) injury.
There are a variety of physiologic factors that affect spasticity, and there are additional physiologic factors yet to be understood that we are actively researching to understand. In spinal cord injury from trauma, spasticity does not begin until about six weeks after injury. For the first six weeks, the muscles are flaccid. After six weeks, spasticity will begin. In spinal cord injury from disease, spasticity typically begins as the disease progresses affecting the nerves and muscles. For individuals diagnosed with stroke, spasticity can begin immediately after time of injury to the brain or later. For those with brain injury, spasticity most often begins about one week after injury. In other neurological diagnoses, spasticity typically develops as the disease progresses. The complications of spasticity include difficulty with activities of daily living. For instance, decreased functional abilities and difficulty with care and hygiene. Additionally, physical changes can occur such as abnormal posture sometimes resulting in breathing difficulty, contractures of the muscles and tendons, and bone and joint deformities. Spasticity can also impede development in children.