Botulinum toxin in the treatment of neurological disorders

The role of botulinus toxin type A in treatment--with special reference to children

Although botulinum toxin A was first introduced to treat strabismus and blepherospasm it is now used in an increasing number of conditions, many in the field of pediatrics. Its action results from a prevention of the release of acetylcholine from nerve terminals. A number of studies recording the effects of the toxin in the treatment of spastic cerebral palsy are reviewed, and although these can be criticized, there seems to be no doubt that it can be of benefit. It is few side effects, but it may reveal an underlying weakness. Other disadvantages are its cost and the need for repeated injections. It can be used for the relief of rigidity, although the effects in the extrapyramidal form of cerebral palsy are not so dramatic. Also it can be beneficial in some forms of dystonia, rarely if this is generalized, but certainly if it is focal, and especially if there is accompanying pain. There are several conditions seen in children, such as strabismus, blepherospasm and tremors, in which this form of treatment will rarely be indicated; but they will be mentioned. An exception may be spasmodic torticollis during adolescence if it does not respond to other therapy, as it is so disabling. Botulinum toxin can be used to block the discharges from cholinergic sympathetic and parasympathetic terminals. Focal hyperhidrosis can be very distressing among older children, and the use of the toxin should sometimes be considered in this and other autonomic disorders.

The mechanism of action of botulinum toxin type A in focal dystonia is most probably through its dual effect on efferent (motor) and afferent pathways at the injected site

OBJECTIVE

To highlight some clinical and physiological features related to treatment with botulinum toxin type A (BTX-A) injections for focal dystonia that may suggest an effect through efferent (alpha motoneuron) and afferent pathways.

DATA SOURCES

This review is based on published clinical and physiological studies as well as personal experience regarding the effect of BTX-A in focal dystonia.

DATA SYNTHESIS

Long or short lag period between BTX-A injections and clinical improvement, remote effect, an effect on the basic physiological characteristics of dystonia, poor correlation between the local weakness and the clinical improvement and alleviation of pain are clinical observations which are difficult to explain on the basis of the known effect of BTX-A on the neuromuscular junction of the alpha motoneuron. These observations as well as recent scientific reports are used to discuss a hypothesis that in addition to its effect as local muscle relaxant, BTX-A acts at the level of the central nervous system (CNS) for 'reorganization'. Such an effect on CNS activity can be mediated through afferent pathways coming from the injected site--possibly originated in muscle spindles. Its effect through afferent pathways on the CNS may be considered as a long-term 'sensory trick'.