Clonus

Clonus Overview

1. CLONUS Ade Wijaya, MD – April 2020

2. Definition Involuntary and rhythmic muscle contractions caused by a permanent lesion in descending motor neurons It is usually considered to be a result of oscillations in the group Ia spinal stretch reflex Hidler JM, Rymer WZ. A simulation study of reflex instability in spasticity: origins of clonus. IEEE Trans Rehabil Eng 1999; 7:327-40.

3. Introduction Clonus is accompanied by spasticity and other findings of reflex excitability It relates to lesions in upper motor neurons Clonus does not occur if the muscle is excessively hypertonic Any mechanism or pharmacological drug suppressing increased reflexes and muscle tone is also prone to block the clonus Severe clonus can interrupt sleep and prevent the transfer capability and result in fatigue that can decrease work performance Interfere with the posture and gait Clonus can also occur in normal individuals Most commonly seen in the ankle joint by briskly dorsiflexing the foot Boyraz I, Uysal H, Koc B, Sarman H. Clonus: definition, mechanism, treatment. Med Glas (Zenica). 2015 Jan 5;12(1):19-26. Zimmerman, B., & Hubbard, J. B. (2019). Clonus.

4. Clonus Reflexes Ankle/Achilles reflex (S1/S2 nerve routes ) Jaw jerk/masseter: Trigeminal nerve, tested at the chin/mental protuberance Patellar/quadriceps/knee: L2 to L4 (mostly L4), tested just inferior to the patella (or by pushing patella distally) Biceps: C5 to C6, just anterior to elbow Triceps: C7 to C8 (mostly C7), just posterior to the elbow Boyraz I, Uysal H, Koc B, Sarman H. Clonus: definition, mechanism, treatment. Med Glas (Zenica). 2015 Feb;12(1):19-26.

5. Pathophysiology S elf-perpetuating reactivation of peripheral muscle stretch circuits, with each beat producing the next Initial appropriate external stimulus that leads to activation of the stretch reflex circuit followed by a central signal which commands the muscles to continue to produce that motor response in the absence of an appropriate stimulation of the stretch reflex This can occur when there is a lesion to descending motor nerves, predominantly the dorsal reticulospinal pathway, which can occur anywhere from the cortex to the spinal cord. The inhibitory dampening effect of these descending nerves on alpha and gamma motor neurons is removed, leading to a hyper excitatory state in the muscle stretch reflex circuit.  Boyraz I, Uysal H, Koc B, Sarman H. Clonus: definition, mechanism, treatment. Med Glas (Zenica). 2015 Feb;12(1):19-26.   Beres-Jones JA, Johnson TD, Harkema SJ. Clonus after human spinal cord injury cannot be attributed solely to recurrent muscle-tendon stretch. Exp Brain Res. 2003 Mar;149(2):222-36. 

6. Etiology CNS LESIONS (BRAIN / SPINAL CORD) SEROTONIN SYNDROME Najari F, Alizadeh-Ghamsari A, Vahabzadeh M, Dadpour B, Reza Mousavi S, Baradaran Kayal I. A Study of the Importance of Clonus Symptoms in Patients with Tramadol Poisoning.J Toxicol. 2017;2017:2151536.

7. Treatment Baclofen Applying cold Botox or phenol injections Boyraz I, Uysal H, Koc B, Sarman H. Clonus: definition, mechanism, treatment. Med Glas (Zenica). 2015 Feb;12(1):19-26.

8. Summary Involuntary and rhythmic muscle contractions caused by a permanent lesion in descending motor neurons It is usually considered to be a result of oscillations in the group Ia spinal stretch reflex Most commonly seen in the ankle joint by briskly dorsiflexing the foot Clonus is accompanied by spasticity and other findings of reflex excitability It relates to lesions in upper motor neurons (CNS lesions / serotonin syndrome) Any mechanism or pharmacological drug suppressing increased reflexes and muscle tone is also prone to block the clonus

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