From the Guidelines
Clonus is primarily caused by damage to the descending motor pathways in the central nervous system, and the main medical causes include upper motor neuron lesions, metabolic disorders, and certain medications, particularly serotonergic drugs like SSRIs, which can lead to serotonin syndrome, as noted in 1. The medical causes of clonus can be categorized into several groups, including:
- Upper motor neuron lesions from conditions such as stroke, multiple sclerosis, spinal cord injury, traumatic brain injury, cerebral palsy, and brain tumors
- Metabolic disorders like hepatic encephalopathy and uremic encephalopathy
- Certain medications, particularly serotonergic drugs like SSRIs, SNRIs, and MAOIs, especially when taken in high doses or combinations leading to serotonin syndrome, as seen in 1
- Stimulants, including amphetamines and cocaine, can also cause clonus Physiologically, clonus occurs when there is hyperexcitability of the stretch reflex due to reduced inhibitory control from upper motor neurons, resulting in rhythmic, involuntary muscle contractions when a muscle is suddenly stretched. Treatment focuses on addressing the underlying cause, and medications like baclofen, diazepam, or dantrolene may help reduce the severity of clonus by decreasing muscle tone or neural excitability. In cases of serotonin syndrome, treatment includes cessation of serotonergic agents, and benzodiazepines may be used in the short-term to manage symptoms, as noted in 1. Additionally, the European Resuscitation Council and European Society of Intensive Care Medicine guidelines suggest that myoclonus, a type of clonus, can be treated with antimyoclonic drugs such as clonazepam, sodium valproate, and levetiracetam, as seen in 1. The most effective treatment approach should prioritize addressing the underlying cause of clonus, and medications should be chosen based on the specific cause and severity of the condition, as well as the patient's overall health status and medical history, with consideration of the potential risks and benefits of each treatment option, as noted in 1 and 1.
From the Research
Medical Causes of Clonus
The medical causes of clonus can be attributed to various factors, including:
- Interruption of the upper motor neuron fibers, such as stroke, multiple sclerosis 2
- Metabolic alterations, such as severe hepatic failure or serotonin syndrome 2
- Permanent lesion in descending motor neurons 3
- Spinal cord injury, which can lead to clonus in muscles paralyzed chronically 4
- Electrical burn injury, which can cause clonus as a delayed neurological complication 5
Specific Conditions Associated with Clonus
Clonus has been observed in various conditions, including:
- Stroke, which can cause ankle clonus 2
- Multiple sclerosis, which can lead to clonus due to interruption of upper motor neuron fibers 2
- Spinal cord injury, which can result in clonus in the lower extremities 4
- Electrical burn injury, which can cause clonus as a late neurological sequela 5
- Severe hepatic failure, which can lead to metabolic alterations causing clonus 2
- Serotonin syndrome, which can cause clonus due to metabolic alterations 2
Characteristics of Clonus
Clonus is characterized by: