Spasticity

Spasticity is an imbalance of the sensorimotor system that demonstrates an increased response to a velocity dependent stretch of the muscle tendon resulting from hyperexcitable muscle stretch reflexes. Spasticity is a small part of the upper motor neuron syndrome composed of increased tone, hyperactive reflexes, weakness, and poor coordination. This hyperexcitability of the alpha motor neuron pool results in the characteristic positive phenomena associated with spasticity. Typically, the upper motor neuron syndrome is characterized by positive and negative symptoms. The positive symptoms are typically the target of therapy with either medication or injections of botulinum toxin. The negative symptoms are due to the damage of the corticospinal tract resulting in weakness, loss of fine motor control, and the Babinski sign. Understanding the source of the positive and negative symptoms can assist the physician in designing a treatment plan tailored for the individual patient. When accessing and treating a patient with spasticity, regardless of the cause, the physician must have knowledge of the patient's lifestyle and the current disability that the patient faces in his or her day-to-day activities. The development of additional tools to treat spasticity is heavily dependent on an improved understanding of pathophysiological mechanisms at both the neurophysiological and the molecular level. Animal models are an indispensable part of spasticity research and are a vital part of future advances in this important area of neuroscience investigation.