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The pathophysiology of spasticity
Author(s) -
Sheean G.
Publication year - 2002
Publication title -
european journal of neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 124
eISSN - 1468-1331
pISSN - 1351-5101
DOI - 10.1046/j.1468-1331.2002.0090s1003.x
Subject(s) - spasticity , clonus , medicine , reflex , neuroscience , triceps reflex , muscle tone , stretch reflex , hypertonia , disinhibition , tonic (physiology) , spastic , muscle spindle , physical medicine and rehabilitation , anesthesia , anatomy , psychology , withdrawal reflex , epilepsy , cerebral palsy , afferent
Spasticity is only one of several components of the upper motor neurone (UMN) syndrome, known collectively as the `positive' phenomena, that are characterized by muscle overactivity. Other components include tendon hyper‐reflexia, clonus, the clasp‐knife phenomenon, flexor and extensor spasms, a Babinski sign, and spastic dystonia. Spasticity is a form of hypertonia due to hyperexcitable tonic stretch reflexes. It is distinguished from rigidity by its dependence upon the speed of the muscle stretch and by the presence of other positive UMN signs. Hyperactive spinal reflexes mediate most of these positive phenomena, while others are due to disordered control of voluntary movement or abnormal efferent drive. An UMN lesion disturbs the balance of supraspinal inhibitory and excitatory inputs, producing a state of net disinhibition of the spinal reflexes. These include proprioceptive (stretch) and nociceptive (flexor withdrawal and extensor) reflexes. The clinical syndrome resulting from an UMN lesion depends more upon its location and extent, and the time since it occurred, than on the pathology of the lesion. However, the change in spinal reflex excitability cannot simply be due to an imbalance in supraspinal control. The delayed onset after the lesion and the frequent reduction in reflex excitability over time, suggests plasticity in the central nervous system. Knowledge of the electrophysiology and neurochemistry of spinal reflexes, together with the action of antispasticity drugs, helps us to understand the pathophysiology of spasticity.