Clonus
Encyclopedia
Clonus is a series of involuntary muscular contractions and relaxations. Clonus is a sign of certain neurological conditions, and is particularly associated with upper motor neuron
lesion
s such as in stroke
, multiple sclerosis
, spinal cord damage
and hepatic encephalopathy
. Unlike the small, spontaneous twitching known as fasciculation
s (usually caused by lower motor neuron
pathology), clonus causes large motions that are usually initiated by a reflex
.
Clonus is most common in the ankle
s, where it is tested by rapidly flexing the foot upward (dorsiflexion). It can also be tested in the knees by rapidly pushing the patella (knee cap), towards the toes. Only sustained clonus (5 beats or more) is considered abnormal.
Clonus appearing after ingesting potent serotonergic drugs strongly predicts imminent serotonin toxicity (serotonin syndrome
).
Upper motor neuron
Upper motor neurons are motor neurons that originate in the motor region of the cerebral cortex or the brain stem and carry motor information down to the final common pathway, that is, any motor neurons that are not directly responsible for stimulating the target muscle...
lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
s such as in stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
, multiple sclerosis
Multiple sclerosis
Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...
, spinal cord damage
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
and hepatic encephalopathy
Hepatic encephalopathy
Hepatic encephalopathy is the occurrence of confusion, altered level of consciousness and coma as a result of liver failure. In the advanced stages it is called hepatic coma or coma hepaticum...
. Unlike the small, spontaneous twitching known as fasciculation
Fasciculation
A fasciculation , or "muscle twitch", is a small, local, involuntary muscle contraction and relaxation visible under the skin arising from the spontaneous discharge of a bundle of skeletal muscle fibers...
s (usually caused by lower motor neuron
Lower motor neuron
Lower motor neurons are the motor neurons connecting the brainstem and spinal cord to muscle fibers, bringing the nerve impulses from the upper motor neurons out to the muscles...
pathology), clonus causes large motions that are usually initiated by a reflex
Reflex
A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. A true reflex is a behavior which is mediated via the reflex arc; this does not apply to casual uses of the term 'reflex'.-See also:...
.
Clonus is most common in the ankle
Ankle
The ankle joint is formed where the foot and the leg meet. The ankle, or talocrural joint, is a synovial hinge joint that connects the distal ends of the tibia and fibula in the lower limb with the proximal end of the talus bone in the foot...
s, where it is tested by rapidly flexing the foot upward (dorsiflexion). It can also be tested in the knees by rapidly pushing the patella (knee cap), towards the toes. Only sustained clonus (5 beats or more) is considered abnormal.
Clonus appearing after ingesting potent serotonergic drugs strongly predicts imminent serotonin toxicity (serotonin syndrome
Serotonin syndrome
Serotonin syndrome is a potentially life-threatening adverse drug reaction that may occur following therapeutic drug use, inadvertent interactions between drugs, overdose of particular drugs, or the recreational use of certain drugs...
).
See also
- MyoclonusMyoclonusMyoclonus is brief, involuntary twitching of a muscle or a group of muscles. It describes a medical sign and, generally, is not a diagnosis of a disease. Brief twitches are perfectly normal. The myoclonic twitches are usually caused by sudden muscle contractions; they also can result from brief...
- Tonic-clonic seizureTonic-clonic seizureTonic–clonic seizures are a type of generalized seizure that affects the entire brain...
- Deep tendon (stretch) reflex