What is Myoclonic Epilepsy of Infancy?
Myoclonic epilepsy of infancy (MEI) is a rare epilepsy form that only lasts for a short period. It’s characterized by short, jerky seizures in otherwise healthy children who are developing normally, and it usually starts in the first three years of life. MEI is often referred to as “benign myoclonic epilepsy in infants” (BMEI), a name coined by Dravet and Bureau in 1981. However, even before their report, there were several other cases which were reported but went by different names, like “myoclonic epilepsy of childhood” by Jeavons.
Despite the use of the term “benign” which usually suggests a mild course, BMEI isn’t always mild or harmless in some children, which led to dropping the word “benign” from the name. According to the International League Against Epilepsy (ILAE), an organization that works against epilepsy, MEI is listed as part of neonatal/infantile epileptic syndromes under a category called Idiopathic generalized epilepsies with age-related onset. In this context, “idiopathic” means the cause of the epilepsies is unknown.
What Causes Myoclonic Epilepsy of Infancy?
Myoclonic epilepsy of infancy is a type of epilepsy that occurs early in life, possibly due to genetics. It’s thought that this type of epilepsy may be caused by genetic factors, with some specific gene changes, such as changes in the SLC2A1 and HCN4 genes, being identified.
About two-thirds of cases of this epilepsy happen without any clear trigger, whereas in about one-third of cases, seizures can be triggered by a sudden noise, touch, or light. This type is known as reflex variant myoclonic epilepsy of infancy. Around 20% of these reflex variant cases might be set off by light stimulation, while the rest could be triggered by a sudden sound or touch.
Risk Factors and Frequency for Myoclonic Epilepsy of Infancy
Myoclonic epilepsy of infancy, a rare form of childhood epilepsy, makes up 1% to 2% of all epilepsy cases in children. However, it is thought that the real number may be slightly higher. Boys are twice as likely to have this condition as girls. Though it typically occurs in children between 6 months and 2 years old, it can also affect children as young as four months or up to five years old.
- Myoclonic epilepsy of infancy is unusual and accounts for 1% to 2% of epilepsy in children, but this might be a slight understatement.
- Boys are twice as likely to get this condition as girls.
- The most common age group for this condition is children between 6 months and 2 years.
- However, it can affect children as young as 4 months or up to 5 years old.
Signs and Symptoms of Myoclonic Epilepsy of Infancy
Myoclonic epilepsy of Infancy affects healthy children with normal development. Generally, they don’t have a significant medical history, but around one third might have had fever-induced seizures before. Also, around 30% of these children have a family history of seizures.
Myoclonic seizures, which are rapid, isolated simultaneous jerks affecting various muscle groups, are the only type of seizures these children experience. These seizures are brief, lasting 1-2 seconds each, and they can happen singly or in clusters. They are often spontaneous and are more likely to occur when the child is awake. The seizures mainly involve the head and upper body. Here’s what you might observe during these seizures:
- Rapid jerks mainly affecting the upper body and head
- Head nodding, eyes rolling upward, blinking
- Falls if the child is standing and lower body is also involved
- Yelling or cough-like sounds, which might occur due to sudden contraction of the diaphragm
Even during these seizures, the child is usually conscious. But when several seizures occur together, the child might appear slightly confused.
Different types of Myoclonic epilepsy of Infancy have been reported. They include:
- Reflex myoclonic epilepsy of infancy, which is triggered by sudden unexpected touch or sound; this type has an earlier onset, shorter duration, and better prognosis
- Photosensitive myoclonic epilepsy, which is a subtype triggered by light and can be hard to manage
- Nocturnal variant, where the jerks only happen during sleep
There’s also a specific type called familial infantile myoclonic epilepsy where the seizures persist into adulthood. This type is genetically inherited and starts in infancy.
Testing for Myoclonic Epilepsy of Infancy
In the evaluation process, one key test is the electroencephalography (EEG), a test that measures brain waves. For MEI, this EEG test might show different findings.
1. The usual brain activity that the EEG measures could appear perfectly normal.
2. Most of the time, the EEG readings between epileptic episodes, also known as “interictal” EEG, appears normal as well.
3. During an episode or “ictal,” the EEG might show short bursts of widespread spike-and-wave patterns or complex spike-and-wave patterns, generally around a frequency of 3 Hz, which is a way of measuring the speed of the brain waves.
4. The EEG might also show discharges that correspond to the myoclonus, the sudden, brief, shock-like jerks.
5. The EEG can sometimes show increased activity when the patient is sleep-deprived. Furthermore, around 20% of people with reflex MEI may exhibit photosensitivity, and flashing light tests can trigger discharges.
Brain scans like MRI, if conducted, will typically appear normal in MEI cases. This sets MEI apart from conditions such as Dravet syndrome or Lennox Gastaut syndrome.
Some patients might undergo genetic testing. This can help doctors rule out certain mutations or changes in the DNA that could cause the condition.
Treatment Options for Myoclonic Epilepsy of Infancy
Myoclonic epilepsy of Infancy or MEI is a condition that often responds well to specific medications designed to control seizures, known as anti-seizure drugs (ASDs). Sodium valproate, also known as valproic acid, is generally the first choice of treatment, and it helps approximately 80% of patients to become free of seizures. If valproic acid isn’t effective, other drugs like Clonazepam and Levetiracetam may be used as alternatives.
After seeing improvements for around 3 to 5 years, doctors will usually start to slowly reduce the amount of ASD medication, a process known as ‘weaning’. However, some cases of MEI, particularly those triggered by sounds (acoustic) or physical sensations (somatosensory), don’t always need treatment, or can be weaned off treatment after just a year. Some forms of MEI are more difficult to manage, like those with photosensitivity which makes a person sensitive to light, and for those, Levetiracetam can be a very effective drug.
It’s important to note that MEI is only one type of myoclonic epilepsy, and other types can be trickier to treat. For West syndrome, for example, treatment typically includes ACTH/corticosteroids or a drug called vigabatrin. Secondary treatments include medications like Clobazam, sodium valproate, and zonisamide. Dravet syndrome can be managed with a combination of ASDs, clobazam and valproic acid for instance, and secondary treatments may involve different drugs or alternative treatments like a special diet (ketogenic diet) or a type of therapy that uses electrical impulses (vagus nerve stimulation).
Other ASDs, such as felbamate, lamotrigine, topiramate, and rufinamide, can be used for Lennox Gastaut syndrome (LGS), another type of epilepsy. The FDA (Food and Drug Administration) in the US has also approved the use of cannabidiol (CBD) oral solution for treating seizures in LGS or Dravet Syndrome, specifically for patients aged two years and older.
What else can Myoclonic Epilepsy of Infancy be?
When diagnosing Myoclonic Epilepsy in Infancy, doctors need to ensure they rule out other non-epileptic conditions that have similar symptoms:
- Hypnagogic jerks, which are harmless jerk movements that usually happen when falling asleep.
- Benign non-epileptic myoclonus of infancy or benign spasm of infancy (BSI), which are non-epileptic spasms (or muscle contractions) occurring in the child’s first year of life and often go away by when they are two years old.
- Benign Neonatal Sleep Myoclonus (BNSM), where there are sudden jerking movements only during non-rem sleep, but the neurological test (EEG) results are normal.
Others conditions that may appear similar include motor stereotypies, benign shuddering spells, myoclonus-dystonia (a type of movement disorder), tics (uncontrollable jerk-like movements), and hyperekplexia (overly jumpy or startle responses).
It’s also crucial to exclude certain specific seizure disorders before diagnosing Benign Myoclonic Epilepsy. These include:
- Dravet syndrome or severe myoclonic epilepsy in infancy (SMEI) is a drug-resistant type of epilepsy that starts in the first year of life in previously healthy kids.
- West syndrome, which is characterized by infantile spasms, irregular neurological (EEG) results, and developmental arrest.
- Lennox Gastaut syndrome has a variety of seizure types, abnormal neurological results, and developmental arrest. It usually arises later in childhood.
- Progressive myoclonic epilepsies (PME) are a group of rare types of epilepsies that progressively worsen, and are characterized by varieties of seizures and failing mental functions.
What to expect with Myoclonic Epilepsy of Infancy
Myoclonic epilepsy of infancy (MEI), a type of seizure disorder that starts in infancy, usually gets better within six months to five years from when it first starts. A subtype of MEI that is triggered by sounds or touch generally has a good outcome and responds well to anti-epileptic drugs (AEDs).
However, another subtype that’s triggered by light is harder to manage. Even after symptoms improve, electroencephalogram (or EEG, a test that checks brain activity) may still show sensitivity to light for several years. About one out of five kids with MEI may also have another type of seizure, known as afebrile generalized tonic-clonic seizures, later on when the anti-epileptic drugs are stopped.
While about two-thirds of kids with MEI show normal development in their cognitive skills and motor abilities, approximately one-third may develop mild difficulties in thinking, behavior, or movement. Starting to have seizures at an early age and having poor control of seizures are risk factors that can lead to a poorer outcome in terms of cognitive abilities.
Possible Complications When Diagnosed with Myoclonic Epilepsy of Infancy
In most cases, seizures in people suffering from MEI get better with time. However, a few people may continue to experience seizures during their teenage years. Fever-related seizures are also common. Moreover, generalized seizures, where the patient loses consciousness and has violent muscle contractions, are seen in 20% of MEI sufferers. In rare cases, MEI may result in juvenile myoclonic epilepsy or other localized forms of epilepsy.
The patient may also face difficulties in certain areas of mental function, such as fine motor skills, attention, general understanding, language, and learning in the long run. Frequent occurrences of seizures at an early age can increase the likelihood of these difficulties.
Side effects from the treatments include behaviour and mood changes when taking levetiracetam, low platelet count, and liver damage when using sodium valproate. The latter is generally not recommended for children younger than 2 years because of the potential for increased liver damage.
It is crucial to keep track of the levels of medication in the body, check blood counts and liver enzyme levels regularly to avoid complications.
List of potential problems:
- Recurring seizures during teenage years
- Fever-related seizures
- Generalized seizures
- Development of other types of epilepsy
- Difficulty with fine motor skills
- Attention problems
- Cognitive trouble
- Language difficulties
- Learning disorders
- Behaviour and mood changes with levetiracetam use
- Low platelet count and liver damage with sodium valproate use
Preventing Myoclonic Epilepsy of Infancy
Parents or guardians caring for a patient need to understand that this specific medical condition is self-limiting, meaning it will naturally get better over time. If anti-seizure drugs (ASD) are used for this condition known as MEI, it’s crucial to discuss the possible risks and benefits of these medications.
Interestingly, even though MEI is a condition that improves on its own and is generally harmless, patients with MEI still need to be regularly monitored. This is to catch any issues with their mental performance, possible struggles at school, or a return of seizures in the future.
It’s also important to talk about potential side effects and complications that may occur when using the anti-seizure drugs. We need to pay special attention to how safe each drug is for the patient. By understanding these details, the patient’s family can make informed decisions about their loved one’s health.
