From the Guidelines
Clonus is a condition characterized by cyclic relaxation and contraction of muscles, often associated with serotonin syndrome, which can be a potentially serious complication of simultaneous use of multiple serotonergic drugs. This condition is marked by involuntary muscle contractions and relaxations, and can be a symptom of various neurological disorders or medication effects. According to the study published in The Journal of Urology 1, clonus is one of the common symptoms of serotonin syndrome, which can also include tremor, hyperreflexia, agitation, mental status changes, diaphoresis, and fever.
Some key points to note about clonus include:
- It is a neurological condition that can result from hyperexcitability of the stretch reflex
- Clonus can be associated with damage to the upper motor neurons that control voluntary movement
- This condition is often seen in patients with neurological disorders, such as multiple sclerosis, stroke, or brain and spinal cord injuries
- Clonus can also be a side effect of certain medications, including serotonergic drugs like SSRIs and TCAs, as mentioned in the study 1
- The severity of clonus can range from mild to sustained, with more pronounced clonus generally indicating more significant neurological dysfunction
In the context of the provided study 1, clonus is discussed as a potential complication of serotonin syndrome, which can occur with the use of certain medications, including those used to treat premature ejaculation. Therefore, it is essential to be aware of the potential risks and symptoms of serotonin syndrome, including clonus, when prescribing or taking these medications.
From the Research
Definition of Clonus
- Clonus is defined as an involuntary rhythmic muscle contraction that generally occurs in people who have sustained lesions involving descending motor pathways in the neuraxis, and is usually accompanied by other signs of reflex hyperexcitability such as spasticity 2.
- It is characterized by involuntary, rhythmic, and brisk muscular contractions in response to peripheral stimuli producing muscle stretching 3.
- Clonus is a series of involuntary, rhythmic, muscular contractions, and relaxations 4.
Causes of Clonus
- Clonus may be caused by interruption of the upper motor neuron fibers such as stroke, multiple sclerosis, or by metabolic alterations such as severe hepatic failure or serotonin syndrome 4.
- It can occur in any muscle with a frequency of 5-8 Hz and the average period of oscillations of the ankle clonus is approximately 160-200 ms 5.
- Clonus is a common pathology that occurs secondary to spinal cord injury (SCI) and other neurological disabilities 6.
Mechanism of Clonus
- The exact mechanism of clonus remains unclear, but two different hypotheses have been asserted regarding the development of clonus 5.
- One hypothesis is that hyperactive stretch reflexes in clonus are caused by self-excitation 5, 2.
- Another alternative explanation for clonus is central generator activity that arises as a consequence of appropriate peripheral events and produces rhythmic stimulation of the lower motor neurons 5.
- The interaction of central mechanisms and peripheral events may be responsible for clonus 6.