2 What Is Epilepsy?
In the previous chapter, we established that a seizure is a single electrical event: a temporary disruption of brain activity. Most people who have a seizure, however, are not automatically diagnosed with epilepsy. Epilepsy is something more specific: it is the condition of having a brain that is persistently prone to generating seizures on its own, without a temporary outside cause.
The formal definition, established by the International League Against Epilepsy, captures this in three scenarios, any one of which is sufficient for a diagnosis.[@Fisher2014] A person has epilepsy if they have had at least two unprovoked seizures more than 24 hours apart. They also have epilepsy if they have had just one unprovoked seizure but the risk of a second seizure over the next ten years is at least 60% — equivalent to the risk that comes with having had two seizures already. And finally, a person has epilepsy if they have been diagnosed with a recognized epilepsy syndrome, even if only one seizure has occurred, because the syndrome itself implies an enduring tendency toward seizures.
2.1 The Word “Unprovoked”
The distinction between provoked and unprovoked seizures sits at the heart of the epilepsy definition, and it is worth understanding clearly.
A provoked seizure — also called an acute symptomatic seizure — occurs because of a temporary, reversible cause acting on the brain. Seizures triggered by a high fever in a young child (febrile seizures), by very low blood sugar, by electrolyte disturbances, by acute alcohol withdrawal, or by a recent head injury or stroke all fall into this category. When the underlying cause resolves, the seizure risk associated with it resolves as well. These events do not, on their own, indicate that the brain is inherently prone to seizures.
An unprovoked seizure occurs in the absence of such a temporary trigger. It suggests that something more enduring — a structural abnormality, a genetic predisposition, an old injury, or a cause that has not yet been identified — has altered the brain’s excitability in a lasting way. This is the kind of seizure that carries a meaningful risk of recurrence and that, under the right circumstances, leads to a diagnosis of epilepsy.
2.2 Why the Distinction Matters
The reason this distinction is not merely academic is that it shapes the decision about whether to start treatment. A child who has a febrile seizure — frightening as that experience is — is not generally started on long-term antiseizure medication, because the seizure reflects a temporary response to fever, not a lasting change in the brain. A child who has two unprovoked seizures, or one unprovoked seizure with a high-risk EEG, is in a different situation, and the conversation about treatment becomes much more pressing.
2.3 What Causes Epilepsy?
Epilepsy is not a single disease with a single cause. It is a broad category of conditions that share the common feature of recurrent, unprovoked seizures — but that can arise from many different underlying mechanisms. The ILAE recognizes six broad etiological categories.[@Scheffer2017]
Structural epilepsy arises from a visible abnormality in the brain — a malformation that was present from birth, a scar from an old injury, stroke, or infection, a tumor, or other identifiable lesion seen on MRI. This category includes focal cortical dysplasia, hippocampal sclerosis, tuberous sclerosis complex, and many others.
Genetic epilepsy is caused by a known or presumed genetic variant that directly leads to seizures. This includes inherited epilepsy syndromes passed down through families, as well as de novo (new) mutations that arise for the first time in the affected child. Importantly, genetic does not mean inherited — many genetic epilepsies arise spontaneously with no family history.
Infectious epilepsy refers to epilepsy caused by a prior brain infection — such as bacterial meningitis, viral encephalitis, or parasitic infections — that has left a lasting change in brain structure or function.
Metabolic epilepsy arises from an underlying metabolic disorder affecting the brain, such as an inborn error of metabolism, a mitochondrial disease, or certain vitamin deficiencies.
Immune epilepsy results from an immune-mediated attack on the brain — including autoimmune encephalitis, in which the body’s own immune system produces antibodies against brain proteins.
Unknown etiology means that despite thorough evaluation, no clear cause has been identified. This remains the case in roughly 40 to 50 percent of people with epilepsy. An unknown cause does not mean untreatable — many people in this category respond well to medication — but it does mean that ongoing advances in genetic testing and neuroimaging may eventually provide an answer that was not available at the time of diagnosis.
2.4 How Common Is Epilepsy?
Epilepsy is one of the most common neurological conditions worldwide. About one in 26 people will develop epilepsy at some point in their lifetime, and approximately 50 million people are living with it globally. It can begin at any age, though onset is most common in childhood and in adults over 60. In children, it is the most common serious neurological diagnosis.
2.5 Is Epilepsy a Lifelong Condition?
Not necessarily. The answer depends heavily on the underlying cause and the specific epilepsy syndrome.
Many childhood epilepsy syndromes are time-limited. Childhood absence epilepsy, for example, resolves in the majority of children during adolescence. Self-limited epilepsy with centrotemporal spikes (BECTS) almost always remits by mid-adolescence. Even among people with epilepsy that persists into adulthood, a meaningful proportion eventually become seizure-free and are able to taper off medication successfully.
The ILAE considers epilepsy to be resolved — not merely controlled, but resolved — when a person has been seizure-free for at least ten years, including at least five years off all antiseizure medications, or when they have passed the upper age limit of an age-dependent syndrome.[@Fisher2014] This is an important distinction for families to understand: epilepsy is not automatically a permanent diagnosis, and the long-term outlook for many children is genuinely optimistic.
For others, particularly those with structural causes or complex genetic syndromes, epilepsy is a chronic condition that requires ongoing management. Even in these cases, the goal — and often the achievable outcome — is the best possible quality of life with the greatest possible seizure freedom.
2.6 What Treatment Can Achieve
Antiseizure medications are effective in roughly two thirds of people with epilepsy, allowing them to become and remain seizure-free.[@Kwan2000] For those who do not respond to medication, other options — including epilepsy surgery, dietary therapies such as the ketogenic diet, and neurostimulation devices — can offer meaningful benefit. These options are discussed in detail in later chapters.
The aim of treatment in epilepsy is not simply to suppress seizures. It is to support the fullest possible life — in school, in relationships, in work, and in the community. Most children with epilepsy, with appropriate diagnosis and treatment, can expect to live full and active lives.
You may hear the words idiopathic, cryptogenic, and symptomatic used to describe epilepsy — particularly in older reports or from clinicians who trained before the current classification system. These terms have largely been replaced by the six etiological categories above, but they still appear in older literature. Idiopathic referred to epilepsy with a presumed genetic basis and no structural cause; symptomatic meant there was a known structural or metabolic cause; cryptogenic meant a cause was suspected but not identified. If you see these terms in your child’s records, your neurologist can help clarify what they mean in context.