Spasticity
Phenol and Alcohol
Phenol and ethyl alcohol have historically been used for chemodenervation in spasticity. Since the introduction of botulinum toxin type A (BTX-A), neither phenol nor alcohol are used as widely as in the past. Of the two, phenol is the more frequently used agent. Although the information below refers specifically to phenol, most of the general considerations apply to alcohol, as well.
Combining Therapies
One of the most important factors in managing spasticity is to pull together all of the available tools, and to pick and choose which ones are best for your specific patient. We have found that it is particularly useful to manage difficult spasticity utilizing several interventions. So for example, if we have a patient with spastic hemiparesis, who has large powerful muscles with a high degree of spasticity, we get a good response by using phenol blockade for proximal large muscles such as the biceps or the thigh adductors, and then using botulinum toxin injections for the smaller distal muscles. At the same time that we may also combine these injection chemodenervation techniques with oral antispasticity agents and physiotherapy or bracing.
The Role of Phenol
The key to the most successful use of phenol in the management of spasticity is patient selection. Clearly, it is important to make sure that the patient and the physician have come to some agreement on their treatment goals and that technically this is something that is achievable. For example, if you have a patient who has generalized spastic quadraparesis and the patient hopes to walk again, that treatment objective may not be possible simply with the phenol block. On the other hand, if you have a patient with a focal area of profound spasticity such as elbow flexion or thigh adduction, then a phenol block may be very successful in achieving that treatment goal.
Mechanism of Action
Phenol’s mechanism of action is to denature protein, causing non-selective tissue destruction in the injected area, including coagulation of nerves and muscle necrosis. Wallerian degeneration of neurons occurs in the weeks following injection. The microcirculation around the nerve may also be affected, possibly accounting for longer-term effects. Most axons eventually regrow, over a variable period of time.
Motor Point Block vs. Motor Nerve Block
There are two different types of phenol injections that have been done historically–the motor point block and the motor nerve block. These are very different procedures with different outcomes and different technical requirements. Both techniques require that the injector understand the functional anatomy of the limb that they are treating, understand how to do electrical stimulation to isolate the nerve, and be skilled in using the needle to put the phenol where it is desired.
The motor point block is an intramuscular injection done generally in the belly of the muscle, utilizing electrical stimulation techniques to isolate the small motor branches of the nerve innervating muscle fascicles. This requires multiple small dose injections using a very careful technique. This gives you a graded response, that is you can get partial or more complete reduction in muscle contraction using this technically very difficult form of injection. While each injection involves only a small volume of phenol, all together the volume can exceed a milliliter or more. Unfortunately, the motor point block is technically much more difficult and the duration of response is extremely variable.
The motor nerve block is also carried out using electrical stimulation, placing the tip of the stimulator as close to the nerve as possible and then infusing a very low volume of phenol, typically a quarter milliliter or less of a 6% solution. When done correctly, you end up with a complete blockade of the nerve.
Summary Table
| Motor nerve block |
Motor point block |
- perineural injection
- low volume of phenol
- complete blockade
- complete reduction of tone
|
- more difficult
- intramuscular injection
- small motor branches targeted
- multiple small dose injections; larger volume
- graded response
- highly variable duration of response
|
Risks
The main risks to be aware of when using phenol for spasticity management have to do first with the risk of poking the patient with a needle–that is, you can injure the nerve that you are seeking to block, or you can inadvertently put the needle into other structures such as a vein or an artery.
Second, there are the risks from the effect of phenol in the tissues themselves. The main problem that we have seen with phenol is when the phenol gets on a mixed nerve and causes initially an area of reduced sensation in the distribution of the sensory nerve, or subsequently, a problem with causalgia or neuralgic type pain as the damaged sensory nerve starts firing with an aberrant signal. There are other reported complications from phenol injections, and these primarily having to do with patients who have received motor point blocks, that is large volumes of phenol, into the forearm, for example. Patients can develop edema in the tissues, venous thrombosis, compartment syndromes, and other more serious sequelae.
At higher concentrations of phenol for example 10%, you end up with a more damaging effect on the nerve–you can denature the axon protein, for example, which can be a permanent effect that is generally not desired in the clinic.
Adjunctive therapies
The relative abrupt decrease in muscle tone after chemodenervation enables therapists to focus on functional treatment goals and implement interventions more quickly and more effectively. In the upper and lower extremities, splinting, bracing and orthotics may be considered if not previously possible, or modified where indicated. Together inhibitory casting and chemodenervation may serve as an effective combination for problematic limb spasticity.
Evaluation Outcomes
Outcomes should be evaluated thoroughly and consistently by a range of clinical measures, including technical accomplishments, functional goals, and patient satisfaction. When the goals of chemodenervation have been defined and outcome measures chosen, evaluation of treatment success should be straight forward.
When patient or caregiver goals have not been met despite functional improvement, the clinical team works with them to reevaluate their expectations. When the functional or technical goals of treatment have not been met, some modification of muscle selection, injection technique or adjunctive therapies may be needed.
Continued lack of efficacy even with optimum technique and muscle selection suggests that the patient was poorly selected for chemodenervation therapy, the technical goals are inappropriate, or the side effects of phenol are debilitating.
Comparison of Phenol with Botulinum Toxin Type A
In comparison with botulinum toxin type A as an antispasticity agent, phenol has advantages in its early onset of action and perhaps longer duration of effect, low cost, and, because of its stability, a greater flexibility in the timing of injections. In addition, its lack of antigenicity means that larger, more powerful muscles may be treated without the potential for antibody response that limits the use of BTX-A.
However, its lack of selectivity on motor function, its tissue-destructive effect, its propensity to cause pain during injections, its troublesome adverse effects, and its vascular reactions may favor the use of botulinum toxin type A therapy in the management of spasticity. As always the patient and caregiver remain at the center of the decision making process.
Traditional Pharmacological Treatments for Spasticity Part I: Local Treaments
Jean-Michel Gracies, MD, PhD; Elie Elovic, MD; John McGuire, MD; David Simpson, MD
Editors: Nathaniel H. Mayer, MD; David M. Simpson, MD
Spasticity: Etiology, Evaluation, Management and the Role of Botulinum Toxin 2002: p52-72.
