EEG can aid in locating the focus of the epileptic seizure. The diagnosis of epilepsy is typically made based on observation of the seizure onset and the underlying cause. An electroencephalogram (EEG) to look for abnormal patterns of brain waves and neuroimaging (CT scan or MRI) to look at the structure of the brain are also usually part of the initial investigations. While figuring out a specific epileptic syndrome is often attempted, it is not always possible. Video and EEG monitoring may be useful in difficult cases. Definition Epilepsy is a disorder of the brain defined by any of the following conditions: : #At least two unprovoked (or reflex) seizures occurring more than 24 hours apart #One unprovoked (or reflex) seizure and a probability of further seizures similar to the general recurrence<unk> (at least 60%) after two unprovoked seizures, occurring over the next 10 years #Diagnosis of an epilepsy syndrome Furthermore, epilepsy is considered to be resolved for individuals who had an age-dependent epilepsy syndrome but are now past that age or those who have remained seizure-free for the last 10 years, with no seizure medicines for the last 5 years. This 2014 definition of the International League Against Epilepsy is a clarification of the ILAE 2005 conceptual definition, according to which epilepsy is "a disorder of the brain characterized by an enduring predisposition to generate epileptic seizures and by the neurobiologic, cognitive, psychological, and social consequences of this condition. The definition of epilepsy requires the occurrence of at least one epileptic seizure." It is, therefore, possible to outgrow epilepsy or to undergo treatment that causes epilepsy to be resolved, but with no guarantee that it will not return. In the definition, epilepsy is now called a disease, rather than a disorder. This was a decision of the executive committee of the ILAE, taken because the word "disorder," while perhaps having less stigma than does "disease," also does not express the degree of seriousness that epilepsy deserves. The definition is practical in nature and is designed for clinical use. In particular, it aims to clarify when an "enduring predisposition" according to the 2005 conceptual definition is present. Researchers, statistically-minded epidemiologists, and other specialized groups may choose to use the older definition or a definition of their own devising. The ILAE considers doing so is perfectly allowable, so long as it is clear what definition is being used. Classification Revised operational scheme of seizure classification, ILAE, 2017 In contrast to the classification of seizures which focuses on what happens during a seizure, the classification of epilepsies focuses on the underlying causes. When a person is admitted to hospital after an epileptic seizure the diagnostic workup results preferably in the seizure itself being classified (e.g. tonic-clonic) and in the underlying disease being identified (e.g. hippocampal sclerosis). The name of the diagnosis finally made depends on the available diagnostic results and the applied definitions and classifications (of seizures and epilepsies) and its respective terminology. The International League Against Epilepsy (ILAE) provided a classification of the epilepsies and epileptic syndromes in 1989 as follows: : #Localization-related epilepsies and syndromes ##Unknown cause (e.g. benign childhood epilepsy with centrotemporal spikes) ##Symptomatic/cryptogenic (e.g. temporal lobe epilepsy) #Generalized ##Unknown cause (e.g. childhood absence epilepsy) ##Cryptogenic or symptomatic (e.g. Lennox-Gastaut syndrome) ##Symptomatic (e.g. early infantile epileptic encephalopathy with burst suppression) #Epilepsies and syndromes undetermined whether focal or generalized ##With both generalized and focal seizures (e.g. epilepsy with continuous spike-waves during slow wave sleep) #Special syndromes (with situation-related seizures) This classification was widely accepted but has also been criticized mainly because the underlying causes of epilepsy (which are a major determinant of clinical course and prognosis) were not covered in detail. In 2010 the ILAE Commission for Classification of the Epilepsies addressed this issue and divided epilepsies into three categories (genetic, structural/metabolic, unknown cause) that were refined in their 2011 recommendation into four categories and a number of subcategories reflecting recent technologic and scientific advances. : #Unknown cause (mostly genetic or presumed genetic origin) ##Pure epilepsies due to single gene disorders ##Pure epilepsies with complex inheritance #Symptomatic (associated with gross anatomic or pathologic abnormalities) ##Mostly genetic or developmental causation ###Childhood epilepsy syndromes ###Progressive myoclonic epilepsies ###Neurocutaneous syndromes ###Other neurologic single gene disorders ###Disorders of chromosome function ###Developmental anomalies of cerebral structure ##Mostly acquired causes ###Hippocampal sclerosis ###Perinatal and infantile causes ###Cerebral trauma, tumor or infection ###Cerebrovascular disorders ###Cerebral immunologic disorders ###Degenerative and other neurologic conditions #Provoked (a specific systemic or environmental factor is the predominant cause of the seizures) ##Provoking factors ##Reflex epilepsies #Cryptogenic (presumed symptomatic nature in which the cause has not been identified) Syndromes Cases of epilepsy may be organized into epilepsy syndromes by the specific features that are present. These features include the age that seizure begin, the seizure types, EEG findings, among others. Identifying an epilepsy syndrome is useful as it helps determine the underlying causes as well as what anti-seizure medication should be tried. The ability to categorize a case of epilepsy into a specific syndrome occurs more often with children since the onset of seizures is commonly early. Less serious examples are benign rolandic epilepsy (2.8 per 100,000), childhood absence epilepsy (0.8 per 100,000) and juvenile myoclonic epilepsy (0.7 per 100,000). Severe syndromes with diffuse brain dysfunction caused, at least partly, by some aspect of epilepsy, are also referred to as developmental and epileptic encephalopathies. These are associated with frequent seizures that are resistant to treatment and cognitive dysfunction, for instance Lennox–Gastaut syndrome (1-2% of all persons with epilepsy), Dravet syndrome(1: 15000-40000 worldwide), and West syndrome(1-9: 100000). Genetics is believed to play an important role in epilepsies by a number of mechanisms. Simple and complex modes of inheritance have been identified for some of them. However, extensive screening have failed to identify many single gene variants of large effect. More recent exome and genome sequencing studies have begun to reveal a number of de novo gene mutations that are responsible for some epileptic encephalopathies, including CHD2 and SYNGAP1 and DNM1, GABBR2, FASN and RYR3. Syndromes in which causes are not clearly identified are difficult to match with categories of the current classification of epilepsy. Categorization for these cases was made somewhat arbitrarily. The idiopathic (unknown cause) category of the 2011 classification includes syndromes in which the general clinical features and/or age specificity strongly point to a presumed genetic cause. Some childhood epilepsy syndromes are included in the unknown cause category in which the cause is presumed genetic, for instance benign rolandic epilepsy. Others are included in symptomatic despite a presumed genetic cause (in at least in some cases), for instance Lennox-Gastaut syndrome. Clinical syndromes in which epilepsy is not the main feature (e.g. Angelman syndrome) were categorized symptomatic but it was argued to include these within the category idiopathic. Classification of epilepsies and particularly of epilepsy syndromes will change with advances in research. Tests An electroencephalogram (EEG) can assist in showing brain activity suggestive of an increased<unk> of seizures. It is only recommended for those who are likely to have had an epileptic seizure on the basis of symptoms. In the diagnosis of epilepsy, electroencephalography may help distinguish the type of seizure or syndrome present. In children it is typically only needed after a second seizure unless specified by a specialist. It cannot be used to rule out the diagnosis and may be falsely positive in those without the disease. In certain situations it may be useful to perform the EEG while the affected individual is sleeping or sleep deprived. Diagnostic imaging by CT scan and MRI is recommended after a first non-febrile seizure to detect structural problems in and around the brain. MRI is generally a better imaging test except when bleeding is suspected, for which CT is more sensitive and more easily available. If someone attends the emergency room with a seizure but returns to normal quickly, imaging tests may be done at a later point. If a person has a previous diagnosis of epilepsy with previous imaging, repeating the imaging is usually not needed even if there are subsequent seizures. For adults, the testing of electrolyte, blood glucose and calcium levels is important to rule out problems with these as causes. An electrocardiogram can rule out problems with the rhythm of the heart. A lumbar puncture may be useful to diagnose a central nervous system infection but is not routinely needed. In children additional tests may be required such as urine biochemistry and blood testing looking for metabolic disorders. Together with EEG and neuroimaging, genetic testing is becoming one of the most important diagnostic technique for epilepsy, as a diagnosis might be achieved in a relevant proportion of cases with severe epilepsies, both in children and adults. For those with negative genetic testing, in some it might be important to repeat or re-analyze previous genetic studies after 2–3 years. A high blood prolactin level within the first 20 minutes following a seizure may be useful to help confirm an epileptic seizure as opposed to psychogenic non-epileptic seizure. 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