What is spasticity?

Spasticity is a well-recognized and potentially important clinical syndrome comprising inappropriate and involuntary high muscle tone. It has been variably defined, with debate still ongoing. Currently, the most widely accepted definition is that of Lance, stating that spasticity is ‘a motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes (muscle tone) with exaggerated tendon jerks, resulting from hyper-excitability of the stretch reflex.’ Unfortunately, even this description does not fully encompass the multifactorial nature of spasticity, since resistance to movement, even in the normal state, is subject to varied contributors. These include patient volition, inertia, visco-elastic muscle forces and range of joint movement, as well as true muscle activation secondary to reflex action. In the real clinical world, it is often not possible to distinguish which of these features is/are dominant. Furthermore, spastic muscle undergoes physiopathological, rheologic change with stiffness, atrophy, fibrosis and finally contracture.