Approach

History is the mainstay of the diagnosis of focal epilepsy. Clinical examination often reveals no obvious abnormality.

Electroencephalogram (EEG) and various imaging techniques may be helpful, although results are frequently normal and these tests mainly serve as supportive investigations.

History

History-taking is the most important aspect of focal seizure diagnosis, yet probably the most difficult to do. As the person experiencing the focal seizure is often unaware of what happens during the seizure, it is important to ask a witness, such as a partner, parent, sibling, or friend, to describe the events. This can be assisted by the witness videoing the events with a smartphone.

Warning symptoms and limb movements

When questioning the patient it is important to ask about warning symptoms, such as abnormal sensations of taste, smell, touch, psychic phenomena (including déjà vu [the sensation of having previously experienced something new] and jamais vu [temporarily not recognising a familiar object or person]), abdominal sensations, and the inability to speak. It should be established whether the episodes involve movements of one or both limbs on one side of the body or all four limbs, in order to distinguish a focal seizure from a generalised event.

Focal impaired awareness seizure

To investigate the possibility of a focal impaired awareness seizure (seizure with impaired consciousness), the physician should ask about purposeless actions known as automatisms (picking at clothes, smacking of the lips), inability to follow commands, and whether the patient stares and becomes unaware of their surroundings. Whether memory loss occurred should also be established. The duration of the spells should be clarified, as most focal impaired awareness seizures last 30-90 seconds.

Medical history

A detailed medical history should be sought. History of head injury, recent central nervous system (CNS) infection, and previous stroke or brain tumour should be established.

Family history of a seizure disorder or any neurocutaneous syndromes (e.g., tuberous sclerosis, neurofibromatosis, Sturge-Weber syndrome) should also be discussed.

Physical examination

The physical examination is often normal; however, the possibility of focal seizures increases if abnormalities are detected on neurological examination. For example, the patient may have a postictal hemiparesis (Todd's paralysis), which is suggestive of a focus in the opposite hemisphere. For patients who are not postictal, a fixed neurological deficit (hemiparesis, unilateral facial weakness) often suggests an underlying structural CNS lesion, which may be associated with focal seizures.

Skin examination should be performed to look for evidence of neurocutaneous syndromes. For instance, the presence of ash-leaf spots, shagreen patches, facial angiofibromas, and/or periungual fibromas is often indicative of tuberous sclerosis. Café au lait spots, axillary freckling, and/or fibromas are suggestive of neurofibromatosis. Port-wine stain is associated with Sturge-Weber syndrome.

Laboratory studies

After a first-time seizure, possible provoking stimuli should be investigated.[36] Laboratory tests include:

  • Electrolyte panel (including sodium, magnesium, and calcium levels): can identify electrolyte disturbances, uraemia, and other metabolic abnormalities that may precipitate a seizure episode

  • Blood glucose: to detect glucose derangements

  • Full blood count: may reveal signs of systemic or CNS infection

  • Toxicology screen: useful if use of illicit substances is suspected

  • Lumbar puncture: helpful if patient has fever, and CNS infection is suspected; contraindicated without prior neuroimaging if the patient has a depressed level of consciousness.

EEG

All patients with a suspected seizure should have an EEG. Although not necessarily diagnostic, it helps to support a diagnosis of focal epilepsy.[37] Other indications include worsening seizure control, new seizure type, patients who have recently switched medication and continue to have seizures, and unknown epilepsy type.

All EEG studies for evaluating suspected epileptic seizures should include awake and sleep recordings, because epileptiform activity is more likely to be recorded during sleep.

Interictal epileptiform discharges (IEDs)

IEDs, represented by spikes or sharp waves, are the most frequent electrographic abnormality identified in routine EEG studies for people with a history of epilepsy.

The sensitivity of the first routine EEG to identify IEDs is approximately 50%, with sensitivity approaching 90% by the fourth EEG or following a 24- to 48-hour continuous EEG study.[38] Therefore, approximately 10% of patients with epilepsy do not demonstrate IEDs on EEG.

Of note, IEDs are seen in 3% of children and 0.5% of adults who do not have a history of epilepsy.[38] The yield of the EEG may be increased by sleep, sleep deprivation, hyperventilation, or photic stimulation, or by placement of additional electrodes to the standard international 10-20 system.

Neuroimaging

CT head

In the emergency department, on an urgent basis, a computed tomography (CT) scan of the head is performed.[39] This is of value in determining acute causes of seizures, such as traumatic brain injury, intracerebral haemorrhage, subarachnoid haemorrhage, or large structural brain lesions. However, CT results may provide limited information, as a bony streak artefact obscures the temporal lobe, which is the most epileptogenic region of the brain. In patients with a known diagnosis of epilepsy, it is not necessary to repeat CT head if they experienced a seizure and were taken to the emergency department.

MRI brain

In the non-acute setting, magnetic resonance imaging (MRI) of the brain is performed with and without gadolinium contrast.[40][41][42] 3-Tesla MRI may lead to increased diagnostic yield. MRI (especially with thin sections through the temporal lobe) identifies small but physiologically important anatomical abnormalities, including mesial temporal sclerosis, neoplastic lesions, vascular malformations (e.g., cavernous malformations), and developmental lesions (e.g., focal cortical dysplasia, nodular heterotopia, schizencephaly and polymicrogyria, as well as hemimegalencephaly).[43] The identification of these pathologies in patients with treatment-resistant focal epilepsy is essential in the planning of surgery.

Other imaging studies

Positive emission tomography (PET) scan, single photon emission computed tomography (SPECT) scan, functional MRI scan, and magnetoencephalography (MEG) scan are mainly used in the detailed planning for epilepsy surgery. Although not required in the initial work-up of epilepsy, these techniques provide important complementary information for the identification of the epileptogenic zone and valuable functional localisation of language and motor cortex.

Functional MRI may be used for language lateralisation prior to epilepsy surgery.[44][45][46] It may also be used to predict memory decline.[47][48]

Video/EEG long-term monitoring

May be useful for those who have had work-up as outpatients and for whom the diagnosis of focal seizures remains uncertain.

The patient is admitted to the epilepsy monitoring unit for continuous video and simultaneous EEG monitoring. The goal is to record the patient's typical clinical events. In addition, the increased EEG sampling may reveal evidence of interictal abnormalities (spikes and sharp waves), which may make the diagnosis of focal seizures more likely.

Alternatively, video/EEG long-term monitoring (LTM) may be used as part of the work-up for localisation of seizure onset in patients with treatment-resistant focal epilepsy who are being considered for epilepsy surgery. The yield of video/EEG LTM in patients with a normal routine EEG is 25% to 40%.[39] If video/EEG LTM is required for pre-surgical evaluation, it is important to record all of the patient's seizure types and to record multiple seizures in an attempt to localise the seizure focus.

Supportive tests

Neuropsychological testing is a comprehensive evaluation of cognitive function (including the various modalities of memory, language, and attention) and visual spatial processing. Deficits in any of these spheres may be observed in patients with treatment-resistant focal epilepsy. For example, memory disturbances may be identified in patients with temporal lobe epilepsy, while attention problems are more common in patients with frontal lobe epilepsy. Patterns of deficits may emerge, which may support the results of the other tests and help to localise the epileptogenic focus prior to surgery.

The Wada test (intracarotid amobarbital test), which is used to confirm the lateralisation of language and to discern memory dominance prior to epilepsy surgery, has increasingly been replaced by functional MRI.[46][47] The Wada test may, however, be indicated when there is a high risk of post-surgical global amnesia (despite its reliability for this purpose being questioned) or when functional MRI fails to show clear left-lateralisation.[44][45][48]

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