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Multiple Sclerosis: Current Status and Strategies for the Future (2001)
Institute of Medicine (IOM)

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133
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Page 133

release of excitatory amino acids. Tizanidine reduces flexor reflexes and spasms and relieves pain. It appears to reduce muscle strength less than baclofen but may not result in measurably better function (see Kita and Goodkin92).

Dantrolene acts within the muscles themselves to produce inhibition of the excitation-contraction coupling process, which leads to reduced muscle strength. Because of its action, it may be better suited for treatment of nonambulatory patients for whom added weakness is less likely to impair mobility. Patients receiving dantrolene should be monitored for liver function because of its potential hepatotoxicity. Benzodiazapines, such as diazepam and clonazepam, act to reduce muscle tone through three mechanisms: suppression of sensory impulses from muscles and skin receptors, postsynaptic potentiation of GABA, and inhibition of excitatory descending pathways. They are generally used in combination with baclofen or other medications.

Intramuscular injections of botulinum A toxin can be helpful, especially for patients with severe localized spasms. The chemical denervation produced by botulinum A toxin can last for up to three months. A study of nine patients with long-standing MS showed reduced spasticity and improved ease of nursing care with no adverse effects.92,163

Recommendations for Further Study of Spasticity in MS

Further research is needed to clarify the mechanisms of spasticity and spasms in MS and to identify opportunities for therapeutic intervention.

  • Determine the spectrum of nerve fiber damage in spinal MS and whether this damage involves monoaminergic systems preferentially.

  • Determine whether the extensor spasm is a product of the locomotion pattern generator and whether this interneuronal circuitry is under descending monoaminergic control.

  • Determine the specific monoamine receptors that influence the stance phase of locomotion and, potentially, the extensor spasms of MS and spinal cord injury (see, for example, Kim et al.89 ).

  • Test the possibility that restoration of 5-HT1b/d or α2 NE action in the spinal cord can lead to restoration of flexion reflex interneuronal excitability and a reduction of flexion spasms.

  • Determine whether flexor spasms can be reduced by reducing the strength of group III and IV afferent input from muscle to spinal interneurons. For example, group III and IV receptors carry substance P and other peptides and make synapses in lamina I of the cord and in the intermediate nucleus as well. It follows that compounds related perhaps to capsaicin may discharge these transmitters from their afferent terminals and reduce the central actions of these afferents.

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