Editing Spasticity (section)

== Spasticity and clonus ==

[[Clonus]] (i.e. involuntary, rhythmic, muscular contractions and relaxations) tends to co-exist with spasticity in many cases of [[stroke]] and [[spinal cord injury]] likely due to their common physiological origins.<ref name="Hidler_1999">{{cite journal | vauthors = Hidler JM, Rymer WZ | title = A simulation study of reflex instability in spasticity: origins of clonus | journal = IEEE Transactions on Rehabilitation Engineering | volume = 7 | issue = 3 | pages = 327–340 | date = September 1999 | pmid = 10498378 | doi = 10.1109/86.788469 | s2cid = 18315004 }}</ref> Some consider clonus as simply an extended outcome of spasticity.<ref name="Hidler_1999" /> Although closely linked, clonus is not seen in all patients with spasticity.<ref name="Hidler_1999" /> Clonus tends to not be present with spasticity in patients with significantly increased [[muscle tone]], as the muscles are constantly active and therefore not engaging in the characteristic on/off cycle of clonus.<ref name="Hidler_1999" /> 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 [[Anatomical terms of location#Proximal and distal|distal]] muscle groups.<ref name="Hidler_1999" /> Clonus is commonly seen in the ankle but may exist in other distal structures as well, such as the knee or spine.<ref name="Wallace_2005">{{cite journal | vauthors = Wallace DM, Ross BH, Thomas CK | title = Motor unit behavior during clonus | journal = Journal of Applied Physiology | volume = 99 | issue = 6 | pages = 2166–2172 | date = December 2005 | pmid = 16099891 | doi = 10.1152/japplphysiol.00649.2005 | s2cid = 8598394 | citeseerx = 10.1.1.501.9581 }}</ref>