Spasticity
Mô tả: Spasticity is increased resistance to passive movement due to an abnormal increase in resting muscle tone. There are three distinct features:4,192 1 Resistance is velocity-dependent (i.e., muscle tone increases with the velocity of passive movement). 2 There is flexor–extensor tone dissociation (i.e., increased tone in flexors of the arms and extensors of the lower limbs). 3 Weakness is present. RELEVANT NEUROANATOMY AND TOPOGRAPHICAL ANATOMY
Nguyên nhân: Common • Cerebral infarction • Cerebral haemorrhage • Lacunar infarction, posterior limb internal capsule • Multiple sclerosis Less common • Spinal cord injury • Mass lesion (e.g. tumour, abscess, AVM) • Progressive spastic paresis • Clostridium tetani • Strychnine
Cơ chế: Spasticity is caused by: 1 upper motor neuron disorder 2 toxicological and infectious disorders (rare). Upper motor neuron disorder Upper motor neuron dysfunction causes a decrease in inhibitory interneuron activity and an increase in gamma motor neuron activity, resulting in a state of hyperexcitability of alpha motor neurons.57 Hyperexcitability of alpha neurons results in increased resting muscle tone and increased resistance during passive movement. In the hyperacute period following upper motor neuron injury, spasticity is often absent. It takes days to weeks for spasticity to develop following acute upper motor neuron injury.39 Toxicological and infectious disorders Clostridium tetani produces a toxin that inhibits the release of GABA from inhibitory interneurons in the spinal cord, causing prolonged excitation of the alpha motor neuron, resulting in spastic paresis.193 Strychnine blocks the uptake of glycine at post-synaptic spinal cord motor neurons, causing prolonged excitation of the alpha motor neuron and spastic paresis.194
Ý nghĩa lâm sàng: Spasticity is most commonly an upper motor neuron sign. Spasticity 398 Internal capsule Pyramidal tract Cerebral peduncle Corticobulbar tract VII XII IX X II Pyramid Pyramidal tract Decussation of pyramidal tract Lateral corticospinal tract Spinal cord Medulla Medulla Midbrain Tongue Jaw Lips Face Brow Thumb Hand Wrist Elbow Shoulder Trunk Hip Knee Ankle Toes Pons
