Traditional pharmacological treatments for spasticity. Part I: Local treatments.

Spasticity is a velocity-dependent increase in stretch reflex activity. It is one of the forms of muscle overactivity that may affect patients with damage to the central nervous system. Spasticity monitoring is relevant to function because the degree of spasticity may reflect the intensity of other disabling types of muscle overactivity, such as unwanted antagonistic co-contractions, permanent muscle activity in the absence of any stretch or volitional command (spastic dystonia), or inappropriate responses to cutaneous or vegetative inputs. In addition, spasticity, like other muscle overactivity, can cause muscle shortening, which is another significant source of disability. Finally, spasticity is the only form of muscle overactivity easily quantifiable at the bedside. Under the name pharmacological treatments of spasticity, we understand the use of agents designed to reduce all types of muscle overactivity, by reducing excitability of motor pathways, at the level of the central nervous system, the neuromuscular junctions, or the muscle. Pharmacologic treatment should be an adjunct to muscle lengthening and training of antagonists. Localized muscle overactivity of specific muscle groups is often seen in a number of common pathologies, including stroke and traumatic brain injury. In these cases, we favor the use of local treatments in those muscles where overactivity is most disabling, by injection into muscle (neuromuscular block) or close to the nerve supplying the muscle (perineural block). Two types of local agents have been used in addition to the newly emerged botulinum toxin: local anesthetics (lidocaine and congeners), with a fully reversible action of short duration, and alcohols (ethanol and phenol), with a longer duration of action. Local anesthetics block both afferent and efferent messages. The onset of action is within minutes and duration of action varies between one and several hours according to the agent used. Their use requires resuscitation equipment available close by. When a long-lasting blocking agent is being considered, we favor the use of transient blocks with local anesthetics for therapeutic tests or diagnostic procedures to answer the following questions: Can function be improved by the block? What are the roles played by overactivity and contracture in the impairment of function? Which muscle is contributing to pathologic posturing? What is the true level of performance of antagonistic muscles? A short-acting anesthetic can also serve as preparation to casting or as an analgesic for intramuscular injections of other antispastic treatment. Alcohol and phenol provide long-term chemical neurolysis through destruction of peripheral nerve. Experience with ethanol is more developed in children using intramuscular injection, while experience with phenol is greater in adults with perineural injection. In both cases, there are anecdotal reports of efficacy but studies have rarely been controlled. Side effects are numerous and include pain during injection, chronic dysesthesia and chronic pain, and episodes of local or regional vascular complications by vessel toxicity. In the absence of controlled studies, a theoretical comparison of neurolytic agents with botulinum toxin is proposed. Neurolytic agents may be preferred to botulinum toxin on a number of grounds, including earlier onset, potentially longer duration of effect, lower cost, and easier storage. Conversely, pain during injection, tissue destruction with chronic sensory side effects, and lack of selectivity on motor function with neurolytic agents may favor the use of botulinum toxin. Neurolytic agents and botulinum toxin may be used in combination, the former for larger proximal muscles and the latter for selective injection into distal muscles. In the future, neurolytic agents may prove more appropriate in very severely affected patients for whom the purposes of the block are comfort and hygiene. (ABSTRACT TRUNCATED)