Spasticity is a condition in which there is an abnormal increase in muscle tone or stiffness of muscle, which might interfere with movement, speech, or be associated with discomfort or pain.Spasticity is usually caused by damage to nerve pathways within the brain or spinal cord that control muscle movement.reatment may include such medications as baclofen, diazepam, tizanidine or clonazepam. Physical therapy regimens may include muscle stretching and range of motion exercises to help prevent shrinkage or shortening of muscles and to reduce the severity of symptoms.