Myonclonus is a sudden “jerky” muscular movement.
Myoclonus can be classified by:
1 – The electrophysiological phenomenon (its electrical characteristics)
- Positive Myoclonus: a contraction of a group of muscles lasting < 300 milliseconds
- Negative Myoclonus (asterixis): a sudden relaxation of a group of muscles
2 – The anatomical origin of the electrical discharge causing the movement
- Cortical myoclonus – from the surface of the brain …. this is associated with seizures and epilepsy
- Subcortical myoclonus – from deeper within the brain
- Spinal or Segemental myoclonus – from an electrical discharge within the spinal cord
- Peripheral Myoclonus – from an electrical impulse within a peripheral nerve (e.g. hemifacial spasm)
3 – By the body part involved
- Focal – If only one body part is affected myoclonus is called “focal” (e.g. myoclonic jerks of the hemiface ( “hemifacial spasm”)
- Segmental – if only one segment of the body is affected, myoclonus is called “segmental” (e.g. hiccoughs)
- Multifocal – if multiple areas body are affected by myoclonus at different times it is called “multifocal” (e.g. poly-mini-myoclonus is a condition where very small myoclonic jerks occur in many different parts of the body in an almost continuous fashion)
- Generalized – If the entire body is affected then myoclonus is called “generalized” (e.g. the startle response)
4 – By timing pattern
Myoclonus can occur in a solitary pattern (“isolated myoclonus”), in repetitive patterns (“rhythmic myoclonus”), just as one falls asleep (“hypnic jerks”), during sleep (“nocturnal myoclonus”), or can create circular patterns of movement (“oscillatory myoclonus”).
5 – By provoking or triggering factors
Myoclonic jerks may be triggered by a variety of stimuli (“stimulus sensitive myoclonus”) including sound, touch, fright/startle, and flashes of light.
Frequently myoclonic jerks occur during an active voluntary muscle contraction, and I called “action myoclonus” (e.g. after lack of oxygen to the brain, and person can develop “post-anoxic myoclonus”).
6 – By cause
- Physiologic myoclonus – myoclonus can occur as a normal phenomenon. Types of normal (“physiologic”) myoclonus include; hypnic jerks (e.g. myoclonus which occurs as a person falls asleep), startle response, exercise or anxiety induced myoclonus, and hiccoughs.
- Primary myoclonus – these are conditions that result in myoclonus which is not secondary to some other medical problem. These primary forms of myoclonus can be inherited (e.g. Essential Myoclonus), or idiopathic (no known cause)
- Secondary myoclonus – there are a large number of varied conditions that can cause myoclonus as a symptom. These include various types of seizure disorders (epilepsy), inherited disorders of metabolism, disorders of brain fatty materials leading to excess build up of these materials (e.g. “storage diseases”, such as Lafora body disease), types of slowly progressive neurologic conditions that may or may not run in families (e.g. spinocerebellar ataxia, basal ganglia degeneration, mitochondrial disorders), and other dementing illnesses (Cruetzfeldt-Jakob disease, Alzheimer’s disease). Infectious diseases of a variety of types (e.g. viral encephalitis, AIDS, syphilis, “mad cow” disease) can have myoclonus as part of their symptom complex. Lack of oxygen can result in damage to nerve cells and lead to myoclonus (post-anoxic myoclonus). Commonly, metabolic disturbances which occur secondary to problems of the liver (e.g. cirrhosis) or lungs (e.g. emphysema/COPD). can cause negative myoclonus (“asterixis”). Local trauma, or other types of injury to the brain, spinal cord, or peripheral nerves can lead to focal myoclonic jerks.
Treatment of Myoclonus
There are a number of medications which can be used to suppress myoclonus.
- First line medications include valproic acid, leviteracetam (Keppra) and clonazepam.
- Various anti-epileptic medications are used as second line agents, including topiramate (Topomax), and zonisamide (Zonegran).
- Third line medications which have shown benefit in some patients included 5-hydroxy-tryptophan (5-HT), and sodium oxybate.
Botulinum toxin injections are typically used to alleviate hemifacial spasm.
Decompressive surgery to remove pressure caused by a blood vessel on the nerve to the facial muscles for hemifacial spasm.