Epileptic seizures are traditionally divided into focal, generalized, combined and unknown epilepsy categories . The classification of seizures by the International League Against Epilepsy (ILAE) is predominantly a descriptive and dynamic process, and if there is a lack of clarity then this should be acknowledged until it is possible to be more certain of the correct epilepsy term .
What is a generalized seizure and what is a focal seizure? (tables 1, 2)
Localized brain networks
Rapidly engaging bilaterally distributed networks in the brain
Generalized involvement. Motor or non-motor
May have retained awareness; usually aware of onset of event even if loss of awareness later
Awareness typically lost and no or minimal memory of event*
Normal; focal neurological findings should anatomically correlate with seizure semiology e.g. hemiplegia
Normal; bilateral or global neurological involvement e.g. cerebral palsy with spastic quadriplegia
Focal discharges; maybe normal. Occasional seizure propagation with bilateral synchrony
Generalized discharges; may also have interictal focal discharges
Normal; focal localized pathology
Normal; usually diffuse brain involvement
Rare but may occur. More in neonatal and infantile age group than adults.
More common than focal seizures. More in neonatal and infantile age group than adults.
Less commonly affected
Aetiology- and epilepsy syndrome-driven. Most people with idiopathic or genetic generalized epilepsies have normal development, whilst infants with early-onset epileptic encephalopathies are severely affected.
*Myoclonic seizures may have retained awareness.
Differentiating features for focal versus generalized epilepsies.
Generalised tonic-clonic seizures
Both limbs, typically symmetrically and simultaneously. Loss of awareness and post-ictal confusion. “Collapse” then tonic in all limbs (10-30 secs), then clonic movements in all limbs, movements more rapid and aggressive, then slow and stop. Patient confused and exhausted.
Generalized spike / polyspike and wave, followed by low-amplitude fast, then high-amplitude spike and wave (often obscured by movement artefact), post-event generalized slowing and attenuation of background.
Multiple but can occur in isolation. Genetic or idiopathic generalized epilepsies
These events can result in hypoxia if prolonged or there are obstructive airway complications or cardiac dysrhythmias.
Abrupt shock-like events. Head only, or upper limbs and trunk, occasionally resulting in injuries. Usually isolated.
A generalized spike and wave or polyspike and wave.
Commonly part of an epilepsy syndrome.JME, LGS
Depending on the syndrome, may have associated co-morbidities e.g. learning difficulties. Commonly other seizures occur. EMG leads are useful to document the duration of contraction and differentiate from spasms or tonic events.
Usually in infants. Typical on awakening and going to sleep. Clusters of sudden extension or flexion of the limbs, crying out and tonic posturing for 1-2 seconds.
Urgent neurological intervention for early treatment to limit brain damage from the epileptiform activity.
Blank stare < 30 secs. Head nodding, eyelid fluttering and occasional hand movements. JAE with some retention of awareness.
3-Hz spike and wave. Abrupt onset and termination typical of CAE. 3-6-Hz spike and wave or polyspike and wave for JAE.
Events can be longer in atypical cases and JAE. In the clinic setting, they can be activated by asking the child to hyperventilate (blow into a windmill).
Abrupt increase in tone involving all limbs
Low-amplitude fast rhythms
Often part of an epilepsy syndrome e.g. LGS
Events more common in sleep.
Abrupt loss of tone
Generalized spike and wave or polyspike discharges, rhythmic slow-wave activity or fast recruiting rhythms.
Often part of an epilepsy syndrome e.g. LGS
Falls occur with no warning. Children need protective head gear. Typically, there is a myoclonic element preceding the atonic event. EMG leads are useful to assess this.
Summary of key features of the common generalized seizure types.
A generalized-onset seizure originates at a point within the brain, and rapidly engages bilaterally distributed networks . In comparison, a focal-onset seizure originates within networks limited to one hemisphere which may be discretely localized or more widely distributed. The result is that the clinical manifestations in the resultant seizures differ according to the network activity.
Epilepsies which include generalized seizures are documented to be more prevalent than focal epilepsies, however, focal epilepsies account for 20% to 66% of incident epilepsies in published studies . Virtually all prevalence and incidence studies report a preponderance of seizures of unknown cause . Such estimates are challenged by a lack of information from many regions and where the quality of the assessment of whether events are generalized or focal is lacking . The wide range documented in studies of focal epilepsies illustrates this.
According to the ILAE 2017 classification of seizures, focal seizures are divided into those in which the affected person is aware and those in which there is impaired awareness [2, 3]. The previous terms used, namely “simple” or “complex partial seizures”, are no longer considered appropriate in the descriptive terminology for focal seizures. Focal seizures are further categorized into those with motor or non-motor features . Motor-onset events include automatisms, epileptic spasms, and atonic, clonic, hyperkinetic, and myoclonic and tonic events; whilst non-motor onset can be autonomic with behavioural arrest, cognitive impairment, emotional change and sensory features.
The ILAE 2017 classification defines generalized seizures under the same headings as focal seizures, i.e. motor and non-motor . Loss of awareness occurs with most, but not all, generalized events, and can be challenging to measure, e.g. in myoclonic seizures [2, 6, 7]. Generalized motor-onset events are tonic-clonic, tonic, clonic, atonic, myoclonic, myoclonic-tonic-clonic, myoclonic-atonic and epileptic spasms, whilst non-motor are absences which can be typical, atypical, myoclonic or eyelid myoclonia .
The ILAE classification also acknowledges that patients may have both generalized and focal seizures, referred to as “combined”.
If a seizure is of unknown onset, useful defining motor (e.g. tonic–clonic) or non-motor (e.g. behavioural arrest) characteristics to the event can still be noted . Targeted follow-up can lead to consolidation of these findings and re-categorization into focal or generalized onset. As such “unknown-onset” is not a characteristic of the seizure, but a term to use whilst awaiting a more definitive categorization. In this setting, as it may not be possible to categorize a patient, a diagnosis of “unknown onset” should be used instead during follow-up.
More detailed descriptions of the semiology of the various focal seizure manifestations and types of generalized seizures are eloquently summarised by the “Instruction Manual for the Operational Classification of Seizure Types” by Fisher et al..
Table 1provides a concise summary of key differentiating features between generalized and focal epilepsies.
Table 2 summarizes the common generalized seizures in relation to their electroclinical semiology, associated epilepsy syndromes and other relevant points.
Table 3 details lateralizing features which can assist in the identification of the focal region of seizure onset, but also highlights features which may assist better delineation of “unknown-onset” cases, as well as where the seizure may still be generalised.
Lateralizing signs to anatomical seizure focus
Lateralizing auras and prodromes
Rare ipsilateral cases reported.
Anatomical location to parietal operculum
TLE more likely ipsilateral.
Non-TLE – not lateralizing
Contralateral correlation in some reports
Some have bilateral sounds
OLE - contralateral hemisphereComplex visual auras (temporal lobe) – mostly commonly reported from the right hemisphere
OLE - homonymous hemifield defects and aurasMore complex visual auras may arise from temporo-parieto-occipital junction
Ipsilateral ictal piloerection
Ipsilateral in most cases
Ictal urinary urge
Right hemisphere in most cases – more TLE
Epileptogenic zone right (non-dominant) mesiotemporal and frontal areas
Lateralizing ictal features
Version – “forced and involuntary movement resulting in sustained unnatural positioning”
Contralateral in the majority
Identifying versive positioning can be a useful sign to recognize GTCS from focal seizures evolving to bilateral generalized seizures. But may not be consistent [6, 12].
Late ipsi-version at the end of generalized seizures [21, 57]
Persistent version during generalization - remains contralateral.Resolution of early version – end recurrence ipsilateral
Late versive movements seen at the end of GTCS.
Unilateral clonic activity
Contralateral in most
Common. Often hand and face involvement. Frontal lobe epilepsy.
Unilateral automatisms and dystonic posturing 
Automatisms predominantly ipsilateral mesial TLE and contralateral neocortical TLE
Dystonic posturing in one arm and automatisms in the other. Mainly TLE.
Automatisms with preserved responsiveness
Right non-dominant TLE
Emotional facial symmetry
Contralateral lower facial weakness in most
Mainly temporal region focus
Right, non-dominant hemisphere in most
Rare. Mainly from TLE patients
Right, non-dominant temporal lobe in most
Unilateral ictal eye blinking
Ipsilateral to the EEG focus in most
EEG changes contralateral to the fast phase of the nystagmus.
Unilateral ictal akinesia / limb immobility
Contralateral in most
Anterolateral region of Heschls’ gyrus (dominant hemisphere) auditory cortex 
Right (non-dominant) TLE
Ictal aphasia and dysphasia
TLE dominant hemisphere
Can be receptive, expressive or mixed aphasia or even dysphasia
Lateralizing language features
Postictal paresis (Todd's palsy)
Contralateral to side of seizure onset
Contralateral to side of seizure onset
Postictal aphasia and dysphasia
Postictal confusion and aphasia can appear similar. Language and speechtesting is important to differentiate.
Postictal nose wiping
TLE – ipsilateralNon-TLE – ipsilateral in about 50%
TLE – when nose wiping occurs: within 60 seconds of seizure end, often using the ipsilateral hand.
Lateralizing postictal features
Postictal flattened affect
Variable but more in right than left hemisphere seizures
Ipsilateral tongue biting
Ipsilateral in most focal seizures
Occurs in focal and generalized seizures
Peri-ictal water drinking
Postictal verbal and visual memory impairment
Left TLE – verbal memory impairmentRight TLE – visual memory impairment
TLE: temporal lobe epilepsy; OLE: occipital lobe epilepsy; FLE: frontal lobe epilepsy. Rows in bold include useful clues to assist recognition that a generalized seizure may have resulted from focal seizure undergoing bilateral generalization.
Lateralizing clinical clues for focal seizures and bilateral generalized seizures (adapted from Loddenkemper and Kotagel, 2005) .
What is the relevance to diagnosing a generalized or a focal seizure?
Once a diagnosis of an epileptic seizure is confirmed, delineating the type of seizure is the next activity recommended on the ILAE roadmap [8, 9]. Clarifying the type of seizure affecting the patient has implications for the aetiology and subsequent investigations . Differentiating between focal and generalized seizures can influence selection of antiseizure medications (ASMs) and referral for epilepsy surgery assessment . Confirming an epilepsy syndrome diagnosis may influence the choice of treatment and the prognosis. Identifying an epilepsy syndrome can also highlight the need to monitor for the development of further seizure types, which may occur as part of a syndrome, or become evident with brain maturation. Infants with West syndrome, consisting of the triad of developmental delay or regression, epileptic spasms and hypsarrhythmia, can evolve to Lennox-Gastaut syndrome in early childhood with new seizure types and requiring different ASMs. Dravet syndrome is associated with different seizure types, manifesting as the affected child becomes older.
Various settings can result in both focal and generalized epileptogenic dysfunctions co-existing, namely diffuse hemispheric abnormalities, multifocal abnormalities, and bilaterally symmetrical localized abnormalities . As such, a neurologic disorder which affects both hemispheres, whilst having a generalized effect on neurocognition and function, can still be associated with focal seizures, generalized seizures or combined seizures. An example of this would be a person with meningitis or encephalitis, in whom both hemispheres incurred insults, and focal seizures resulted from various regions independently of each other. Accordingly, diagnosing focal seizures does not necessarily equate to an isolated area of brain involvement, and extensive networks can still be involved.
How can one differentiate generalized from focal seizures?
Differentiating between focal and generalized epilepsy is traditionally based on the combination of clinical history, detailed description of seizure semiology, physical examination, inter-ictal EEG, imaging data, and if possible ictal video-EEG (vEEG) recording . The process can be complex.
As illustrated in tables 1, 3, it is useful to consider the key differentiating features between generalized and focal epilepsies.
The anatomical region of the seizure onset influences the clinical manifestation of the event. For example, seizures which commence in networks in the frontal lobe are typically more involved in higher intellectual or motor functions, the parietal lobe with simple sensory components and temporal lobe with emotion, hearing and smell, whilst the occipital lobe is involved with vision. Table 3, adapted from the comprehensive report by Loddenkamper and Kotagel, provides a detailed summary of lateralizing features supportive of an anatomical ictal focus .
Generalised seizures are typically considered to be associated with loss of awareness, but subtle signs are described in the prelude to an event, and affected individuals may be conscious of “trigger” activities or settings that place them most at risk . Usually this is immediately (seconds) before the ictal event, but may permit the affected individual to sit down or reach out to someone . However, there are some generalized seizure disorders with retained awareness during the ictal event. This is reported in patients with juvenile myoclonic epilepsy [7, 16].
An adult-based study explored seizures with altered awareness and minimal motor involvement, to identify differentiating features between focal seizures and generalized seizures . In this study, 10 of 16 patients had recall of vEEG documented generalized seizures. Automatisms in this group were not found to be reliable differentiating events. Similarly, whilst head deviation was found more frequently in patients with focal seizures, it also occurred to a lesser extent in those with generalized seizures . However, preceding aura was only recorded in patients with focal seizures and as such, if identified, is a reliable delineating event. Sensory unilateral auras tend to be contralateral to structural lesions and can assist epilepsy surgery planning, especially when they are well localized .
Seizures of short duration (. The same study reported that eye blinking was also more evident in patients with generalized seizures. However, another study of 180 seizures from 50 patients with medial or neocortical temporal lobe epilepsy found that patients over 18 years of age were more likely to blink during seizures compared to those in the childhood and adolescent age group . They suggested that there was a developmental influence for the manifestation. As such, blinking during a seizure is not a reliable sign to differentiate between focal- and generalized-onset seizures.
The differentiation between generalized seizures and focal seizures which have evolved to bilateral generalized seizures can be challenging. In children with generalized seizures, mouth-opening during the event and post-seizure motor movements are more likely to occur in the setting of focal seizures with bilateral generalized seizures .
Versive events which equate to forced and involuntary movements, resulting in sustained unnatural positioning, are often contralateral to the side of seizure onset . This sign is considered useful when present in generalized seizures suspected to be of focal onset evolving to bilateral generalized seizures . However, versive events are also reported in generalized-onset seizures . Overall, if version occurs immediately before the tonic-clonic phase of a seizure, is associated with neck extension, and also associated with late ipsiversion after the end of a generalized tonic–clonic seizure, these features support a focal-onset event .
Asymmetric seizure termination, whereby the last clonic jerk is ipsilateral to the hemisphere of seizure onset, supports generalized seizures as bilateral generalized with focal-onset. .
Asymmetric tonic limb posturing during a seizure manifests typically with one arm flexed at the elbow, and the other extended, often referred to as the “sign-of-4”. Patients with bilateral generalized seizures, inclusive of asymmetric tonic limb posturing, have an ictal focus contralateral to the extended arm in most cases, especially patients with TLE .
Patients with idiopathic generalized epilepsies do not have unilateral dystonic posturing compared to patients with TLE in whom it is common, when bilateral tonic-clonic seizures occur [24, 25].
Post-ictal states can also provide useful differentiating features. Todd's palsy always equates to the contralateral side of the focal seizure onset . Postictal confusion can be challenging to differentiate from aphasia following a focal seizure originating from the dominant hemisphere. In this setting, speech and language assessment of expressive, receptive and mixed aphasia is important.
What information is important to access from the patient or caregiver?
The personal and familial medical history is important to assimilate. Explore events in the patient's history which might represent risk factors for developing epilepsy. Examples include a peri-natal insult, traumatic brain injury, meningitis or encephalitis, brain tumour or history of prolonged febrile seizures in childhood for adult patients . Familial history of epilepsy or neurological diseases is also important with regard to genetic disorders, such as tuberous sclerosis complex (TSC). Furthermore, familial history of epilepsy and hereditary predisposition is not unusual in patients with idiopathic generalized epilepsy .
What are useful semiological characteristics of seizure types
In order to differentiate these different types of seizures, the clinician needs to consider a “detective style” approach which would allow him/her to clearly visualize the seizure semiology that probably occurred. This approach requires attaining all available details from the patient as well as witnesses, for ideally more than one event. This is particularly important for patients who are not aware during the event. People with bilateral tonic-clonic evolution are often mislabelled as having generalized seizures, hence the importance in the details of the onset of the event. Accordingly, the witness should have been present from the start of the event , in order to give details of the initial semiology that might be consistent with a focal onset, as illustrated in table 3. Additional important clinical clues include establishing what the affected person was doing before the event started and if there was a change in their normal routine (less sleep or food, more stress, an intercurrent illness, etc.) . Establishing if there are reproducible triggers to the event can support a diagnosis of epilepsy, for example, in the reflex epilepsy groups whereby events can be caused by reading, thinking or eating . In the setting of a person who appears to be unaware, it is important to verify whether this was confirmed by lack of response to tactile stimulation.
Questions should be culturally appropriate using terminology which is understood by laypersons in their local setting. Questions should also be sensitive to the stigma often carried by having epileptic seizures and associated caution is needed as this results in reticence in divulging the full nature of associated events . Providing the witness or caregiver with illustrations of the suspected events can be useful. As such, the clinician must become adept at performing clonic movements, myoclonic jerks and absence events to demonstrate typical events to witnesses. A caregiver may struggle to estimate the duration of an event especially in the setting of anxiety and concern of watching a “loved-one” seize. Demonstrating that a myoclonic jerk lasts a micro-second (shock-like) rather than being held for a few seconds (spasm or tonic seizure) is useful. Counting the seconds can help a caregiver estimate the duration in which a child with absence seizures is unresponsive. Lastly, the witness should also be asked whether they noted a change in behaviour of a person with epilepsy prior to the seizure event, for example, emotional lability, confusion, agitation, and so on.
In addition to the clinical description of the event, asking witnesses to point to the affected side of the patient can avoid potential confusion between left and right laterality. Erroneous documentation of laterality can lead to an assumption of poor anatomical correlation or that the person with epilepsy has more than one focal area of seizure involvement. Also, asking the witness to demonstrate a facial expression or movement that they saw can be very useful to differentiate between tonic, clonic, myoclonic or automatisms. Individuals are unwittingly biased in their interpretation of observations across multiple levels which includes assumptive terms used during witness descriptions and the clinician assimilation of this information provided . Several witnesses can observe the same event and provide completely different descriptions . For this reason, it is important to keep an open approach and to repeat the clinical history and description of the events often. Start with open-ended questions, such as “describe what you saw” and move to closed questions; “did his eyes go to one side”, “point to the arm that moved”, “could he talk to you after the event”, etc. Always ask about the state of the person with epilepsy at the end of the event, specifically if they are weak or have impaired movement following an event (Todd's palsy), also whether they can speak after an event and are able to correctly name common objects. Impairment in any of these areas would support a focal region being affected (table 3).
Asking the person with epilepsy what they remember of the events and whether they were all the same also assists with differentiation and localization. For example, a child with self-limited childhood epilepsy with centrotemporal spikes will often report an inability to speak at the start of the event but will retain language comprehension. Attaining this information aids both anatomical localization but also syndromic diagnosis. Other tools to incorporate include asking children to draw what they feel happens to them both during a seizure and how the condition makes them feel about themselves. Whilst a child may struggle to say how they feel or what they experience, they all learn to draw from an early age and often find this an easier way to express what happens to them .
In the current age of the smartphone, clinicians and caregivers are becoming increasingly engaged in the use of this as a tool to delineate seizure types. In some cases, this can be exceptionally useful, sparing the person with the events the need to undergo further costly or invasive interventions. The quality of the captured event tends to be the restricting element for the tool. The start of the events are rarely captured and, as illustrated above, this is vital in the setting of delineating both the semiology of a focal epileptic seizure and to be able to differentiate from a generalized-onset seizure .
What aspects of the clinical examination are important?
Clinical examination is important. Evidence of focal pathology, such as a hemiplegia, would support the anatomical region of concern being due to a focal aetiology. Examination may be relatively unremarkable and require subtle neurological screening to detect functional asymmetry, such as the Fogg manoeuvre in which the patient is asked to walk on the outer lateral boarders of their feet (feet inverted at the heels) and this destabilization in the gait leads to a clawing of the affected arm. Subjects may become habituated to this sign, therefore it is only useful in the early stages of routine examination. Evidence of a neurocutaneous syndrome may support a disorder such as tuberous sclerosis complex (TSC). Whilst over 80% of people with TSC have seizures which are focal in the majority, it cannot be assumed that this is the case without further exploration . In a person with generalized epilepsy, especially those of genetic aetiology, clinical examination may be normal. However, other cases with structural or infective aetiologies may reveal clues of a global brain disorder, for example, microcephaly. As such, the finding of abnormal neurology can be useful to support a neurological process, but again, this would not necessarily be specific for focal versus generalized seizures. As stated earlier, the involvement of both hemispheres does not automatically dictate that an associated epilepsy is focal or generalized. For example, evidence of dysmorphology and cognitive delay may suggest a generalized brain disorder, but without clinical supporting evidence, associated seizures cannot be assumed to be generalized.
How can one differentiate between focal and generalized seizures using EEG?
Electrophysiological (EEG) studies are useful supporting tools in the differentiation between focal and generalized seizures and also to define the type of focal or generalized epilepsy [33, 34]. For example, absence epilepsy exhibits a 3-Hz spike and wave, juvenile myoclonic epilepsy exhibits generalized spikes and photosensitive response evident in a third of affected people, epileptic spasms show the classic hypsarrhythmia, and so on (figures 1-6). When delineating between myoclonus and spasm events, attachment of electromyography (EMG) surface leads aids monitoring of the period of muscle activity correlating to the duration of the event. If the awake EEG is normal, then proceeding with a study in natural sleep, often enhanced by preceding sleep deprivation, can be useful. An EEG with normal background activity is not useful to differentiate between seizure subgroups . If diagnostic doubt remains as to whether the events are ictal or not, or focal and generalized cannot be distinguished, then admission for vEEG prolonged recording can sometimes resolve this, as this tool is the gold standard intervention to support a diagnosis. Whilst this is time-consuming, costly and often inconvenient for the person with events and their caregivers, correct event delineation early in the disease course permits accurate diagnosis and management, avoiding the unnecessary legacy of mistreatment. Juvenile myoclonic epilepsy can manifest with focal myoclonic jerks leading to misdiagnosis of focal epilepsy; in this setting, vEEG capturing of ictal events is invaluable to delineate the process .
Care must be taken in the interpretation of the EEG as some people with generalized seizures are still able to generate independent focal interictal discharges, and focal discharges do not always correlate to the anatomical localization of the epilepsy [36-39]. This is common in patients with juvenile myoclonic epilepsy and juvenile absence epilepsy  (figure 3). In addition, incidental focal discharges are not uncommon in the general population. Surface electrode ictal recordings can be challenging if the propagating focus is deep as this can result in the appearance of asymmetry in the surface electrodes with an apparent focal “take-off” suggesting a focal onset to the event. Paradoxically, a deep focus can also result in the appearance of generalized activity on the ictal recording as the focal generating network is not detected until bilateral synchrony has occurred (figure 4).
What is the role of neuroimaging in differentiating between focal and generalized seizures?
Neuroimaging is recommended by the ILAE Epilepsy Neuroimaging Task Force . This can assist with anatomical location of seizure focus, as well as understanding aetiology, treatment implications and prognosis. The study by Baykan et al. found that, in the setting of minimal motor seizures with loss of awareness, MRI for generalized seizures is usually normal but for patients with focal seizures, abnormalities are often identified . However, as with EEG, neuroimaging should not be used as the only tool to differentiate between focal and generalized seizures but rather a supporting aid. Other neuroimaging tools can be useful, especially in MRI-negative cases with suspected focal pathology, these include positron emission tomography (PET) and single-photon emission computer tomography (SPECT) .
Other aetiology-driven investigations
Well-defined seizure semiologies can lead to targeted investigations for genetic, metabolic and immune aetiologies and result in precision medicine management. For instance, faciobrachial dystonic seizures are almost pathognomic of limbic encephalitis associated with LGI1 antibodies . In young adults, association of primary generalized tonic-clonic seizures, myoclonus, new-onset cerebellar ataxia and slight cognitive impairment should result in genetic testing for type 1 progressive myoclonic epilepsy.
What are the pitfalls and how can one avoid them? (table 4)
Focal-onset seizures can evolve into bilateral tonic-clonic seizures
Assume seizure is generalized.
Ensure the start of the event has been witnessed
Focal seizure symptoms, and focal EEG abnormalities.
Focality can manifest in primary generalized epilepsies
Be certain that the focal features are truly related to focal aetiology
Laterality of focal seizures
Caregivers often confuse which side was affected
Ask caregiver to point to the affected side on the patient
Seizures with generalized body stiffening
Differentiate between myoclonic, spasms and tonic seizures
Demonstrate shock-like myoclonus and spasms (1-2 seconds) or tonic events held for >2 seconds
Duration of seizure event
Caregivers may struggle to remember duration of event – often over calling duration of seizure
Try counting or tapping to help the caregiver estimate duration of the event.Ask them to estimate duration in-line with a common activity e.g. boiling a kettle.
Difficult to identify focality
Seizures may only be recognized from the major motor component which dominates, and the semiology of the seizure onset is missed.
Age at presentation
Seizures in infants
Brain maturation affects seizure expression e.g. focal pathology may express as epileptic spasms
Generalized brain pathology may not manifest as generalized tonic-clonic seizures until the brain reaches an adequate stage of maturation. Similarly, as affected by stages of brain maturation, events may transiently manifest as epileptic spasms but in fact have underlying focal pathology.
Sensory seizures in young children
Young children may lack communication skills to describe sensory symptoms
Sensory seizures may be missed in young children
Childhood-onset epilepsy transitioned to adulthood
As children transition through adolescence and into adulthood, seizures change or resolve but other co-morbidities may dominate
Tuberous sclerosis complex and Dravet syndrome are examples of this. Consider ASM adjustments and attention to behavioural co-morbidities.
Seizures in the elderly
Seizures can mimic conditions and equally be missed in the setting of other diseases e.g. dementia, stroke
Diverse potentially misleading findings from normal interictal EEG, to bilateral synchrony misdiagnosed as primary generalized epilepsy and inter-ictal focal discharges manifesting in generalized epilepsies
The EEG findings must always be assessed in conjunction with the clinical and, when indicated, neuroimaging findings.
Risk of exacerbation of epilepsy
Always consider the potential adverse effects of ASMs
Epilepsy in children with loss of awareness
Differentiate absence from temporal lobe epilepsy
Absence of usually less than 30 seconds with no post-ictal phase
People with movement disorders and stereotypies
Tics, anxiety, intellectual disability and autism spectrum disorder can occur in the setting of epilepsy or compound recognition of epilepsy
Clinicians should be aware that these co-morbidities can compound differentiation with seizures as they can occur independently of seizures and erroneously be diagnosed as seizures, but may also co-exist with seizures.
Pitfalls that can lead to misdiagnosis of focal and generalized seizures.
Focal-onset seizures can evolve into bilateral tonic-clonic seizures and if the start of the event is not witnessed then the clinician may be misled into believing that the event is the clinical expression of a generalized epilepsy. On the other hand, focal seizure symptoms, as well as focal EEG abnormalities, can manifest in primary generalized epilepsies and be misleading  (figure 3).
Age at presentation
Age can complicate the delineation of focal from generalized seizures. Young children may be unable to express sensory symptoms, and as such, events from the temporal lobe, for example, are easily missed and under-reported . Further brain maturation can influence the manifestation of seizure events, and generalized tonic-clonic seizures do not manifest in infants until adequate myelination has occurred, usually after 12 months of age . In line with brain maturation time windows, an infant may manifest with epileptic spasms related to an underlying structural focal pathology. The spasms in this setting may be focal, but not always. As people with epilepsy age, the manifestation of events may vary and other co-morbidities can compound the recognition of seizure types, for example, distinction between early stages of dementia and focal seizures in the elderly, and notably transient epileptic amnesia that might be difficult to identify and require targeted investigations [46, 47].
ASMs can also complicate the manifestation of seizures, for example, children with focal seizures, which may be syndromic (namely self-limited childhood epilepsy with centrotemporal spikes or Lennox-Gastaut syndrome), are often managed with lamotrigine as add-on therapy but this can exacerbate or bring out myoclonic seizures in some patients, leading the clinician to question the original diagnosis . Further, self-limited epilepsy of childhood with centrotemporal or occipital spikes in children may evolve into encephalopathy with status epilepticus during sleep (ESES) when treated with carbamazepine, phenobarbital or phenytoin .
Childhood absence epilepsy can commonly mimic the loss of awareness reported in sensory focal seizures . Clinicians may not be aware that simple automatisms are common during childhood and juvenile absence epilepsy. In this setting, children are placed on carbamazepine and suffer exacerbation of their absence epilepsy or myoclonus . This is an important illustration of how relevant the clinical history is to clarify the difference in the two settings. In comparison to sensory focal seizures, absence events exhibit abrupt onset and termination, duration of less than 30 seconds and no post-ictal confusion. Juvenile myoclonic epilepsy is another condition often misdiagnosed as focal epilepsy, especially as asymmetrical myoclonic jerks are not infrequent [51, 52].
Children or adults with co-morbidities, inclusive of tics, anxiety, intellectual disability and autism spectrum disorder, can have an overlay of additional movements, behaviours and compromised expression which can further challenge delineation of seizure semiology. The diagnosis of patients with psychogenic non-epileptic seizures can be extremely challenging and these events can co-exist in the setting of epilepsy as well [53-56].
The differentiation between generalized and focal seizures remains a clinical process based on meticulous clinical history and examination. EEG, neuroimaging and other investigations (genetics, immune markers, etc.) can support the outcome but distinction between focal and generalized epilepsy in isolation is rarely achieved using such techniques. Certain clinical settings such as age, underlying aetiologies, and co-morbidities will be more predisposed to specific types of epilepsy, but again this is a guide and not a fixed modality.