Epilepsy is a common neurological disorder that is characterized by a predisposition to having epileptic seizures and can take many clinical forms and have a veritable Augean stable of etiologies.
Epilepsy is defined by the International League Against Epilepsy (ILAE) as 1:
at least two or more unprovoked (or reflex) seizures occurring more than 24 hours apart; or
one unprovoked (or reflex) seizure and a probability of further seizures similar to the general recurrence risk after two unprovoked seizures, occurring over the next 10 years; or
diagnosis of an epilepsy syndrome
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Epidemiology
Epilepsy is very common, with approximately 3% of the population affected at some point in their life 2.
Clinical presentation
The hallmark clinical feature of epilepsy is that of epileptic seizures, which may have a variety of semiologies depending on the type of seizure and epilepsy. However, there are other important clinical features that may accompany epileptic seizures in epilepsy 3:
psychiatric co-morbidity, e.g. anxiety, depression, functional seizures
physical effects/complications of epileptic seizures, e.g. injury, death (including sudden unexpected death in epilepsy (SUDEP)), neurocognitive deterioration
social effects/complications: e.g. lower education levels, lower employment rates with fewer options, limitations on recreational activities, stigmatisation
antiseizure medication side-effects, e.g. neurocognitive deterioration, weight gain, rash, osteoporosis, hair loss
Pathology
Epilepsy is classified by the International League Against Epilepsy (ILAE) according to a three-level framework 4:
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seizure type 5
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focal (preferred term to 'partial') onset
may have awareness (preferred term to 'simple partial') or impaired awareness (preferred term to 'complex partial' or 'dyscognitive')
may be motor onset or non-motor onset (e.g. sensory, autonomic)
may progress from focal to bilateral tonic-clonic seizures
-
generalized
may be motor seizures, e.g. tonic-clonic (preferred term to 'grand mal') seizure, clonic seizure, tonic seizure, myoclonic-tonic-clonic seizure, myoclonic-atonic seizure, atonic seizure
may be non-motor or absence (preferred term to 'petit mal') seizure
unknown
-
-
epilepsy type
focal
generalized
combined generalized and focal
unknown
-
epilepsy syndrome
Etiology
There are a myriad of etiologies, however, in adults with new onset of seizures ~50% will not have a determinable cause 2. The International League Against Epilepsy (ILAE) have proposed the following etiological classification 4:
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structural etiology
acquired, e.g. stroke, cerebral palsy, post-meningitis, traumatic brain injury, vascular malformations, mesial temporal sclerosis, meningoencephaloceles, tumors (e.g. long-term epilepsy-associated tumors, low-grade gliomas, etc.)
genetic, e.g. focal cortical dysplasia, grey matter heterotopia
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genetic etiology
e.g. channelopathies (e.g. Dravet syndrome), neurocutaneous syndromes (e.g. tuberous sclerosis)
note that some genetic etiologies may also be structural etiologies in this classification
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infectious etiology
e.g. neurocysticercosis, tuberculosis, toxoplasmosis, cerebral malaria, subacute sclerosing panencephalitis, congenital CMV
note that this is not referring to seizures occurring in the setting of an acute CNS infection
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metabolic etiology
e.g. porphyria
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immune etiology
unknown etiology
Radiographic features
MRI
MRI brain is the radiographic modality of choice 2. Please see articles on specific conditions listed above for imaging features. There are a number of MRI protocols that can be used to investigate patients with seizures.
Nuclear medicine
SPECT
If perfusion neuroimaging is performed during a seizure (i.e. ictal SPECT), it can be useful for localizing the epileptogenic zone 6,7. Postictal SPECT and interictal SPECT are less sensitive than ictal SPECT 12, however, ictal-interictal SPECT subtraction, particularly with MRI co-registration (i.e. subtraction ictal SPECT co-registered to MRI (SISCOM)), can be highly sensitive 13,14.
FDG-PET
May show an area of hypometabolism corresponding to an epileptogenic zone. Largely replaced by MRI but can be used in conjunction for localization of an epileptogenic zone 8.
PET-TSPO
Translocator protein (TSPO) is a molecular marker for glial activation and neuroinflammation. Quantification of TSPO using PET has been recently used to study epileptogenic zone. For example, increased TSPO levels can be seen in the epileptogenic zone within temporal lobes in patients with temporal lobe epilepsy 9,10.
Treatment and prognosis
Management of epilepsy is potentially complex, and may involve 2,3:
lifestyle restrictions, e.g. driving restrictions, restrictions on employment, limiting exposure to drugs and alcohol
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antiseizure medications, either as monotherapy or in combination, and ketogenic diet
describing these medications as 'antiseizure' is the International League Against Epilepsy (ILAE) preferred terminology to 'antiepileptic' or 'anticonvulsive' 11
epilepsy surgery, e.g. stereo EEG, surgical resection, neuromodulation therapies
specific management of psychosocial effects/complications