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 identified by symptoms such as tremor, hyperreflexia, agitation, mental status changes, diaphoresis, and fever 1. Clonus can be a sign of upper motor neuron damage, but in the context of serotonin syndrome, it is a result of the excessive stimulation of serotonin receptors. The treatment of clonus depends on the underlying cause, but in the case of serotonin syndrome, it involves cessation of serotonergic agents and may include the use of benzodiazepines to manage symptoms 1.
Some key points to consider when evaluating clonus include:
- The presence of other symptoms such as tremor, hyperreflexia, and agitation, which can indicate serotonin syndrome 1
- The potential for clonus to be a sign of upper motor neuron damage, which may require further evaluation and treatment 1
- The importance of distinguishing clonus from other movement disorders, such as tremor or myoclonus, as the treatment approaches may differ significantly 1
- The need for caution when prescribing serotonergic agents, such as SSRIs, due to the risk of serotonin syndrome, particularly in patients with a history of bipolar depression or suicidal ideation 1.
In terms of management, cessation of serotonergic agents is the primary treatment for clonus associated with serotonin syndrome, and benzodiazepines may be used in the short-term to manage symptoms 1. Additionally, physical therapy, muscle relaxants, or botulinum toxin injections may be considered for the treatment of clonus due to other underlying causes. However, the treatment approach should be individualized based on the specific cause and severity of the condition.
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.