The Use of Botulinum Toxin in Children with Muscle Stiffness: An Update
This Keeping Current is one of a series of reports that discuss the effectiveness of rehabilitation interventions for children and youth with brain injury. When reading this Keeping Current, you will notice that the research reviewed is often taken from studies involving children and youth with a variety of neurological conditions and diagnoses. Be critical when deciding what information relates to your situation. The most relevant information will come from studies that specifically address the diagnosis in question. However, be aware that research findings from studies involving children with one specific diagnosis may be relevant for children with other diagnoses when their functional difficulties are similar, even if the causes are different.
The Economical Insurance GroupSupport for the research to conduct this critical review comes from a grant from The Economical Insurance Group
What is Botulinum Toxin?
When injected into a muscle, Clostridium botulinum toxin type A (BTA) produces a local, temporary weakness that is associated with a decrease in muscle stiffness (spasticity). Over the last 25 years, BTA has been used to treat many neuromuscular conditions including strabismus (crossed eyes) and vocal cord spasm. In the last ten years, BTA has been used in children with cerebral palsy and traumatic brain injury who have muscle stiffness. It is thought that decreasing the children's muscle stiffness will allow for better stretching of shortened muscles, increased range of motion and opportunities to strengthen muscles that work opposite to the muscle that has been injected.
These changes should allow the children to learn better control of their movement and to improve their motor function.
How does BTA work?
(The following section presents a brief overview of the technical and biological aspects of BTA. Some readers may wish to skip this section.)
Botulinum neurotoxins are produced by certain strains of Clostridium bacteria and are classified into 7 serotypes, A through G (Shantz & Johnson, 1992). Most clinical work has been done with serotype A. The biological effects of BTA are well understood. An injection of BTA into the muscle creates a localized muscle paralysis by causing a highly specific binding to presynaptic cholinergic peripheral nerve terminals. The toxin is then internalized into the nerve terminal and inhibits the release of acetylcholine at the neuromuscular junction. Neurotransmission recovers when the axon terminal sprouts new nerve endings and forms new synaptic contacts on adjacent muscle fibers (Jankovic & Brin, 1991). Over time the original neuromuscular junction starts to work again highlighting the reversible nature of the treatment (De Paiva et al., 1999). In humans within two to three days of the injection, the muscle becomes weak with a reduction in tone, reaching a maximum effect at two weeks. The reduction in muscle tone lasts an average of three months with gradual increase in tone and gain in muscle strength occurring after this time. Effects from BTA can still be noted up to 6 months after the injection.
Are there side effects?
BTA injections are well tolerated with few serious side effects. The primary side effect is weakening of nearby muscles. The impact this has on the individual depends on the muscle group that has been injected. For instance when injecting neck muscles, the most frequent side effect is difficulty swallowing which generally improves after two weeks. In children receiving leg muscle injections, BTA can lead to short-term stumbling when walking. Temporary urinary incontinence has been reported following hip muscle injections in 1% of the children (Bakheit et al., 2001). Whole body side effects have been rare, with generalized weakness and fatigue reported in less than 1% of children injected (Bakheit et al., 2001). The individual experiences some pain at the time of the injection (similar to receiving an immunization needle) and can develop mild soreness at the injection site.
The effects of BTA injections are temporary and repeated injections are often required. The individual can develop antibodies to the toxin and become resistant to its effect. Repeated BTA injections may not be as effective in these individuals (Hermann et al., 2000). Antibody formation has been observed in a small number of patients (less than 10%) who have received repeated injections of BTA. The dosage and frequency of the injection are felt to be the two important factors affecting antibody formation (Jankovic & Brin, 1991).
What do we know about the Use of BTA in Children with Muscle Stiffness?
Many research articles have been published on this topic. For this article, the studies have been grouped into four main areas:
- Management of Spastic Equinus (toe-walking)
- Multiple Lower Extremity Injections
- Upper Extremity Injections
- Use in Children with Head Injury
The research studies discussed in this article use a variety of research designs. Some of the designs provide stronger evidence than others. To help you determine which studies provide the best evidence about the effectiveness of BTA, we have rated each article according to its strength of evidence. A score of 1 represents the strongest or best evidence and a score of 5 is the weakest. Roman numerals are commonly used when rating research evidence and they will be used in the rest of this article (1 = I, 2 = II, 3=III, 4 = IV, 5 = V).
The following descriptions of Levels I to V are based on the rating system used by the American Academy for Cerebral Palsy and Developmental Medicine. For further information on the rating system, please go to their website (click on 'Committees', click on 'Treatment Outcomes', click on "Methodology for Developing Evidence Tables and Reviewing Treatment Outcomes Research").
A Level I study is a large trial where subjects are assigned randomly to either an intervention group or a control group (this is similar to flipping a coin). A Level II study is a study of an intervention and a control group, but assignment to the group is not done randomly. Level I and II studies are prospective - that is, interventions and assessments are done after the study begins. Level III studies involve a comparison between the outcome of an intervention group and a control group - information about one or more of these groups would have been collected in the past. Unlike the first 3 levels, Level IV and V studies do not have a control or comparison group - this makes it difficult to know whether it was the intervention or something else that caused the changes seen in the participants. In Level IV studies the outcome of interest is typically measured before and after an intervention. Level V studies are descriptions of cases or expert reports.
Within each area we have also given an overall grade for the evidence with "A" being the highest (evidence supported by one or more Level I studies) and "C" being the lowest (evidence supported at best by Level III, IV, and V studies).
Use of BTA for Management of Spastic Equinus (Toe-Walking)
Most of the research on BTA has been done in children with cerebral palsy who toe-walk (equinus gait). Several studies provide a high level of evidence and are summarized in Table 1. There is grade "A" evidence (the highest level) for improvement in walking over the short term (up to 3 months after the injection). One study has shown long-term effectiveness (greater than two years) of repeated BTA injections on walking. The impact of repeated injections to help prevent muscle contractures and decrease the need for orthopedic surgery is currently under evaluation.
Use of BTA in Other Leg Muscles
There is less evidence available for injections of other leg muscles. Table 2 outlines the studies in children with cerebral palsy that have examined multiple lower extremity injections.
A few studies have shown a decrease in stiffness of the hip adductor muscle and an improvement in gross motor function. These studies have lacked control groups and the current evidence is graded as "C" (the lowest level).
Two studies of BTA injections in the hamstrings have demonstrated improvements in muscle flexibility, knee extension during walking, and walking speed. However, again due to the lack of a control group, the strength of the evidence can only be graded as "C".
Multilevel injections were used to look at the effect of "high" versus "low" dose injection of BTA over a 12-week period (Wissel et al., 1999). Improvements were found for muscle tone, range of motion and quality of walking. Children who received the high dose improved the most. The evidence is graded as "B plus" (high level of evidence shown in only one study).
Continued work needs to be done to determine which muscles should be targeted in multilevel injections, what an appropriate dose of BTA would be, and whether BTA will be helpful in treating hip subluxation (partial dislocation of the hip joint).
Use of BTA in the Upper Extremity
Table 3 outlines studies that have been done in children with cerebral palsy who have arm and hand stiffness. There is evidence for improved range of motion (flexibility), function, and cosmetic appearance of the arm and hand in the majority of children receiving the BTA injections. The strength of the evidence is graded at an "A" level. Most studies followed children for up to six months. The role of repeated injections over time requires further investigation. Continued work is being done to evaluate the best dose and injection techniques for the arm and hand muscles.
Use of BTA with Individuals with Traumatic Brain Injury
Very little research on BTA has been done in children with traumatic brain injury. Use of BTA in individuals (aged 16-54 years) who were at various stages of recovery has been studied (see Table 4). There is evidence of increased range of motion, decreased stiffness, decreased pain, and increased ease of cleaning the arm and hand (likely related to increased range of motion). Overall, the evidence for the use of BTA in adults and young adults is graded at a "C" level. Although more research is needed to justify the use of BTA to treat muscle stiffness in children with brain injury, it appears that BTA will be helpful.
Overall, there is good evidence for the use of BTA in children to decrease muscle stiffness, improve motor function and improve range of motion of limb joints for up to three to six months after the injection. More information is required to evaluate the long-term effects of BTA.
Update written by:
Darcy Fehlings MD MSc FRCP(C), Physician Director Neurodevelopmental Program, Bloorview MacMillan Centre; Division of Neurology, Hospital for Sick Children; Assistant Professor, University of Toronto
Ka-Kei Yeung, PT, Physiotherapist, Bloorview MacMillan Children's Centre
Rachel Teplicky, OT Ont. (Reg.), Research Coordinator, CanChild Centre for Childhood Disability Research
Want to know more? Contact:
CanChild Centre for Childhood Disability Research
Institute for Applied Health Sciences, Room 408
1400 Main St. W., Hamilton, ON L8S 1C7
Tel: 905-525-9140 x 27850 Fax: 905-522-6095
Table 1: Use of BTA for Management of Spastic Equinus (Toe-walking), Table 2: Use of BTA in Other Leg Muscles, Table 3: Use of BTA in the Upper Extremity and Table 4: Use of BTA with Individuals with Traumatic Brain Injury