What is muscle spasticity?
Muscle spasticity can be a significant functional problem in children with any injury or disease that has involved the brain or spinal cord (central nervous system, or CNS). With injury to the CNS, the nerves to muscles outside the CNS (peripheral nervous system, or PNS) are no longer under voluntary control by the brain.
When this occurs, the nerves of the PNS begin to activate muscles on their own without the control that is usually provided by the brain. As a result, the muscle can begin contracting without relaxation, which is the cause of spasticity.
The spasticity is evidenced by an increase in muscle stretch reflexes (i.e., knee jerk with tapping of the tendon) and clonus (rhythmic, repetitive movement of a joint when its muscle is suddenly stretched and held).
When moving a spastic limb through its range of motion, one feels a resistance to movement that increases with the speed at which one moves the limb. This is the definition of spasticity, but other terms such as increased muscle tone, hypertonicity, spastic dystonia, or flexor / extensor spasms are used to describe this same problem. In clinic the term "muscle spasticity" will be used to reduce confusion of terms.
Why treat muscle spasticity?
If spasticity is left untreated, it can progress to a permanently contracted state with joint deformity. This is especially true in joints where a muscle group that moves the joint in one direction is much more powerful than the muscle that moves the joint in the opposite direction (muscle imbalance).
Examples of how this imbalance can affect a joint is at the ankle with foot position (always points toes or up on toes when walking) or at the wrist with hand position (hand in flexion with difficulty in grasping). Once a contracture occurs (inability to bring the joint involved through its full range of motion, even with forceful / prolonged stretching) it can be difficult to re-establish full range of motion at that joint without surgical intervention.
Aggressive, early treatment of spasticity is required for contracture prevention that will allow a child to achieve their best potential functional activity.
How are contractures prevented?
Prevention of contractures begins with determining what is limiting a child from either actively (moving oneself) or passively (being moved by someone else) moving his joints through a full range of motion. In some cases, this can be due to destruction or abnormality of the bones around a joint or problems with the ligaments and tissue around that joint.
With abnormal joint movement and inactivity, muscles can shorten and contract. In the case of muscle spasticity, the joint and soft tissue can be normal, but with constant contraction of a muscle because of spasticity there is the potential for permanent shortening of the muscle. When it can no longer stretch to allow movement through full range of motion, a contracture can occur. Agents that lessen the spasticity of the involved muscles best prevent this type of contracture.
What is the benefit of treating muscle spasticity?
The goals of treatment of muscle spasticity are individualized for every patient in our clinic. These goals can include decreasing pain from muscle spasms by reducing both the frequency and intensity of the spasms or increasing the range of motion of joints to allow improved function. Improvement of range of motion can be helpful in several ways:
- Improving hygiene: easier toileting and bathing
- Improved fitting of orthotics (braces and splints)
- Improved functional activity: seat position, standing, walking, upper extremity use
- Possibly delaying surgery for tendon lengthening to a time when outcome would be improved
How can the spasticity be treated?
To attain these goals, a thorough evaluation needs to be done for that child to determine what would be the most appropriate management. Therapists are many times the first individuals to do an in-depth evaluation of a child with impairments due to spasticity.
Initiation of stretching programs by therapists along with encouraging good alignment and positioning for functional activities are usually the first interventions done to address the problem of muscle spasticity. If range of motion continues to be a problem, further evaluation by a physician who has experience with muscle spasticity could be helpful.
Following such an evaluation, a physician could prescribe oral medications that can reduce spasticity in muscles and are most helpful in children who have widespread muscle spasticity. Since these medications are given orally, they spread throughout the body and affect all muscles (skeletal muscles, not muscles as in heart or blood vessels) to some degree.
In many children, there are a few muscle groups in particular that can have very active spasticity and a more focal approach to these muscles would be better than a widespread approach. In this case a physician may recommend a nerve block to interrupt the signal to the particular muscle that is spastic. Once the signal that is carried to the muscle by the nerve is interrupted, the spasticity will decrease.
There are several types of nerve blocks that can be used to decrease spasticity including phenol, ethanol and botulinum toxin. Of these, botulinum toxin has the best combination of spasticity relief with ease of use and fewer complications.
What is botulinum toxin and where does it come from?
The botulinum toxin itself is the same toxin that can develop from bacteria in improperly canned foods. The botulinum toxin used for injection is purified from this bacterium, clostridium botulinum, and freeze-dried for future use.
The toxin was first used for medical purposes in the late 1970s for injection into eye muscles but had originally been purified in the 1940s. There are eight different types of botulinum toxin that have been isolated from the clostridium botulinum bacteria, of which type A is the most potent.
Botulinum toxin type A (BTA) is sold under the trade name Botox. There is another manufacturer of BTA in France, and this product is sold under the name Dysport. There is also botulinum toxin type B (BTB), which is sold under the brand name Myobloc. The Division of Pediatric Rehabilitation at Cincinnati Children's routinely uses the Botox brand of BTA.
When is botulinum toxin used?
Following an examination by both a therapist and physician, the use of botulinum toxin for focal relief of muscle spasticity can be recommended as the best way to address a child's functional problems. Once the problem muscle groups are identified and goals for that particular child discussed, the injection of botulinum toxin can be done if there are no permanent contractures of the muscle groups.
It is important that both the physician and therapist communicate with each other when these injections are done. Increase in therapy frequency and change in bracing or splinting may be indicated following the procedure.
Therapy after botulinum toxin injections is always done to ensure that full advantage is taken of the reduction in spasticity.
How is the botulinum toxin given?
The actual procedure of injecting botulinum toxin is relatively simple. These injections do not differ significantly from injections of other medications. It is more of an issue to decide before injections are done, what is the potential outcome based on muscle groups injected.
Also, decisions are made as to how much botulinum toxin to use, how many sites to inject, and how concentrated the botulinum toxin should be. Once these issues are clarified, an appointment for injection of botulinum toxin is made.
A concern of both parents and children is whether these injections will be painful. There is no pain associated with the action of the toxin itself, only with the needle injections. To lessen this problem, the skin where the injections will be done is coated with EMLA cream (2.5% lidocaine and 2.5% prilocaine) prior to the procedure. This anesthetizes the skin; the child may still feel pressure from the needle and also sensations in the muscle itself. Just the fact that a child is having a procedure done and is being held in place is probably more upsetting than the actual needle injection especially in preschool children.
All children injected in our clinic have done very well immediately following the injections and are sent home without any emotional upset. We seldom use sedation, rather, we use distraction and quick injection technique. In rare cases, localization of a muscle may be necessary using an electromyograph machine (EMG) or electric stimulator, this would be discussed with family prior to scheduling the injections.
Are there any problems from receiving these injections and are they permanent?
There are no restrictions in activity following the botulinum toxin injections; children may resume their usual activity and therapy. Onset on action of the toxin can be seen within a few hours of the injections; changes in spasticity may continue for up to one to two weeks.
A follow-up visit is usually scheduled at around 3 months following injection to determine if result were beneficial and if effect is wearing off. The effect on muscle spasticity by botulinum toxin is temporary and lasts for approximately five months. This also varies with the amount of toxin injected, the size of the muscle, the degree of spasticity in the muscle, and interventions as therapy and bracing.
Many times effects on spasticity are longer lasting. It is unclear whether this is due to breaking down patterned movements (many muscles contracting together rather than singly) or from allowing weak muscles to strengthen over time that had previously been overpowered by more spastic muscles pulling against them. It is therefore important that there be close follow-up after the injections to determine an appropriate course of treatment.
Re-injection of the same muscle groups have been done. There are no restrictions to re-injections as long as they are at least 3 months apart. Keeping injections this far apart reduces the risk of antibody formation by the child's immune system which can make future injections ineffective.
Long-term follow-up studies of children receiving these injections are not available at this time given that this is a relatively new use of the toxin. There have been no reports of significant long-term problems in patients receiving these injections to eye muscles, which have been done since approximately 1980.