A sign on examination of abnormal muscle tone in which the muscles contract reflex-ively to being stretched. spasticity increases with the speed and direction of the attempted movement since it is activated by stretching. spasticity is what occurs after injury to the brain or upper parts of the spinal cord, like a stroke, cerebral palsy, or multiple sclerosis, that involve the pyramidal motor system (motor cortex and its primary motor pathways through the brain and spinal cord). Pyramidal tract lesions also display abnormally elevated reflexes and true weakness.
Extrapyramidal disorders such as Parkinson’s disease that involve the basal ganglia are instead associated with rigidity, an increase in stiffness does not change with the speed of movement. The presence of spasticity, or other signs of pyramidal tract lesions, in a person with parkinsonism (signs of extrapyramidal dysfunction) would be a sign of either a second disease, or a diagnosis such as multisystem atrophy (MsA), progressive supranuclear palsy (PSP), or disorders other than Parkinson’s disease.
