 Clonus results due to an increased motor neuron excitation (decreased action potential threshold) and is common in muscles with long conduction delays, such as the long reflex tracts found in distal muscle groups.Clonus is commonly seen in the ankle but may exist in other distal structures as well, such as the knee or spine.The clinical underpinnings of two of the most common spasticity conditions, spastic cerebral palsy and multiple sclerosis, can be described as follows