Spasticity is a frequent symptom in MS that is seen to a greater or lesser extent in up to 75 percent of patients. It is a complex, poorly understood symptom that is often associated with muscle weakness. In MS, the lower limbs are more markedly affected by spasticity than the arms. Spasticity may be associated with pain, painful extensor and flexor spasms, clonus, and underlying weakness. Extensor spasticity of the legs, particularly of the quadriceps, might be considered advantageous for standing, walking, and transferring. However, sudden loss of tone may also occur when the muscle reaches a certain crucial length as a result of increasing resistance and progressive stretching. Spasticity is associated with structural changes in the muscles (thixotropy) leading to further resistance to movement and shortening. Functionally, spasticity can reduce mobility and dexterity; spasms may prevent transfers, hinder comfortable sitting and lying postures, and affect sleep.

The treatment of spasticity should not be aimed at its removal per se, but rather at improving function, easing care, or alleviating pain. Key components in the management of spasticity include patient education, physiotherapy input, and the judicious use of drug treatment. This should include awareness that noxious stimuli, such as urinary tract infections, bowel impaction, and ingrown toenails, may worsen spasticity. The importance of correct positioning in lying and sitting, and the value of a standing programme should be emphasized. Treatment may be divided into oral therapy, drugs given by other routes (intrathecal, intraneural, or intramuscular), and surgery. It must be remembered that whatever treatment is chosen, expert monitoring is required. Furthermore, MS-related spasticity tends to change over time, and it is important to reevaluate treatments at regular intervals.

There are few trials of anti-spasticity agents in MS. However, they usually involve small numbers of patients in which the pattern of spasticity is inadequately described, the objectives of treatment are not specified, and only short- to medium-term outcomes are assessed. In clinical practice it is suggested that only one substance be used at a time, although there may be a rationale for combining drugs if a single agent is ineffective or only partially effective. Of the available agents, baclofen has undergone the most evaluation (both the oral and intrathecal routes). Tizanidine has been the most recently licensed drug in the United Kingdom and the United States. Most of the studies were carried out 20 to 30 years ago, and many focused on spinal cord injury. The management of severe spasticity may be best provided by a multidisciplinary clinic that incorporates neurologic, physiologic, and physiotherapy expertise, and can provide a wide range of treatment options.