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What is Clonus

Clonus is an involuntary muscle contraction, which is oftenfound to be rhythmic and repetitive in nature. This condition is an extremetype of hyperreflexia (increase of deep tendon reflexes). It can affect thewrists, kneecap, patella or ankles. In most cases, ankles are the part of the bodyaffected by clonus, and the problem is usually caused by abnormality in theneuromuscular activity, which provoked deep tendon reflex. Stretched musclesare very common cause of clonus in the ankle. Sometimes, you can notice clonusin the ankle while trying to hold still the joint muscle, when the foot is jerkingup and down.

Clonus can be a serious problem, and neurologists willusually perform several tests to determine the root cause of the problem. CT (computedtomography) and MRI (magnetic resonance imaging) scans of the spinal cord, thebrain or even the brain stem can be of great help to diagnose the condition.X-rays of the spine and spinal fluid or myelography are some of the additional testsavailable for diagnostic purposes.

Lesions that affect motor neurons in the spinal cord or thebrain are one of the identified causes of clonus. Because of the lesions, thereis no inhibition of muscle contraction, no stop sign for them and they continueto contract, provoking stiffness and increased reflexes.

What Can Cause Clonus

As already said, brain and spinal cord lesions are knowncauses of clonus, but this condition is also present in serotonin syndrome.

Clonus can be the result of any process that has affected motorneurons in the brain. Very young children who experienced this condition are atincreased risk of developing additional symptoms of cerebral palsy. Adultpeople suffering from brain injuries, strokes or tumors are frequently known toexperience hyperreflexia and clonus. ALS (amyotrophic lateral sclerosis) and MS(multiple sclerosis) can also be identified as the causes of clonus.

Lesions in the spinal cord are proven to increase deep tendonreflexes and lead to clonus. Tumors, abscesses, injuries of the spinal cordcausing paralysis can be the reason because of which a patient suffers fromclonus. Transverse myelitis is yet another cause of clonus. This condition isprovoked by the inflammation of the spinal cord that can be viral, bacterial,immune-related or even associated with systemic lupus erythematosus (SLE). Paraplegia,hyperreflexia and spasticity of the muscles are also present in peoplesuffering from hereditary spastic paraparesis.

Serotonin syndrome can affect patients combiningantidepressant from the group of SSRI – serotonin specific reuptake inhibitorswith some other antidepressants, migraine drug or even painkiller medication. Thesepatients experience fever, agitation, confusion, rigid muscles and clonus and hyperreflexiaas the characteristics of the syndrome.

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