Approach
Generalised tonic-clonic seizures (GTCSs) occur in many different types of epilepsy, and making an accurate diagnosis based solely on a described or even observed GTCS is difficult. It is also important to determine the following:[29][30] EpilepsyDiagnosis.org Opens in new window
If the episode is in fact a seizure as opposed to another event that merely resembles one (e.g., syncope, functional [non-epileptic] seizure, panic attack, movement disorder, sleep disorder, stroke, migraine, etc.).
If a GTCS is truly an unprovoked seizure event; a variety of provoking insults can cause GTCSs in a patient who does not have epilepsy.
If the seizure is confirmed as an epileptic seizure and no provoking stimulus can be identified, the next step is to determine if there is an underlying generalised-onset epilepsy versus a focal-onset epilepsy; this is necessary to direct the appropriate treatment steps. This can be accomplished through careful history, and the use of electroencephalogram (EEG) and/or magnetic resonance imaging (MRI) studies; occasionally long-term video-EEG monitoring (telemetry) is necessary to fully characterise the epilepsy syndrome.
If it is determined that the GTCS reflects generalised-onset epilepsy, further categorisation is necessary, based upon a careful assessment of seizure types, age of onset, family history, response to therapy, and supportive data. A history of other generalised seizure types may be of use; these include clonic, tonic, myoclonic, myoclonic-tonic-clonic, myoclonic-atonic, atonic, and non-motor (absence) seizures.[1] Any given patient may experience one seizure type or any combination of multiple seizure types, depending on the underlying epilepsy syndrome. Therefore, presentations vary, and a complete synthesis of the patient's history, examination, and supportive data is necessary to form a diagnosis.
History from patient and witnesses of seizure
Because GTCSs are often brief, self-limited events, they are sometimes not observed directly by healthcare providers. Thus, a detailed history from the patient and available eyewitnesses is often critical to the evaluation. Videos recorded by observers using a smartphone can be extremely valuable in helping the clinician to determine if the episode is epileptic or not and, if so, provide information about the seizure type.[31]
Premonitory symptoms or signs. A description of specific and stereotyped neurological signs and/or symptoms either before or after a seizure can provide information about the type of epilepsy. In cases of seizures with focal onset, the patient may describe a warning (sometimes referred to as an 'aura') consisting of an unusual sensation or experience; examples include a rising epigastric experience, fear, déjà vu, or an 'out-of-body' sensation. Patients commonly have difficulty describing their aura.
A description of the observed sequence of events. The patient or an observer may be able to comment about unilateral or asymmetrical features of the seizure progression; one side of the body may exhibit tonic or clonic features prior to the other. Alternatively, an observer may describe sudden convulsive activity in all limbs simultaneously. After the convulsion stops, an observer may also notice a significant hemiparesis or aphasia that improves over time.
Duration of the events. Patients and observers often have difficulty assessing an accurate duration of the actual seizure. Practitioners should take care to glean an accurate history of the exact duration of the convulsion, and of the postictal state (e.g., confusion and amnesia). Most convulsive seizures last less than 3 minutes, and the true duration of an event can be useful in making an accurate diagnosis.
Other signs: tongue-biting or urinary incontinence. These features are relatively non-specific regarding the type of seizure, but can be useful in determining if a true seizure has occurred.
Physical examination
If a practitioner does witness an event, he/she must carefully observe the characteristics of the seizure itself, noting any asymmetry in the progression of signs and the speed with which generalised convulsive activity develops. After the seizure, the practitioner can examine the patient for alertness, language capabilities, and any asymmetry in motor strength or dexterity.
Outside of a seizure event, any focal neurological deficits on examination may be evidence of a structural lesion resulting in symptomatic epilepsy. This may include evidence of a primary language, memory, visuospatial, or executive function disturbance; visual field deficit or asymmetric weakness; or muscle tone and/or deep tendon reflex abnormality.
Some physical signs (neurocutaneous findings) may suggest an underlying neurological disease that is associated with seizures.
Laboratory evaluation
After a first-time seizure event, the practitioner should search for possible provoking stimuli. Laboratory testing can include:
Electrolyte panel: can identify electrolyte imbalances, uraemia, other metabolic abnormalities.
Blood glucose: to detect glucose derangements.
Full blood count: may reveal signs of infection.
Toxicology screen: useful if illicit substance use is suspected.
Lumbar puncture: useful if central nervous system infection is suspected, if the patient is not returning to baseline, or if there is persistent neurological deficit.
Diagnostic lumbar puncture in adults: animated demonstrationHow to perform a diagnostic lumbar puncture in adults. Includes a discussion of patient positioning, choice of needle, and measurement of opening and closing pressure.
Several studies demonstrated that serial measurements of serum creatine kinase (CK) can differentiate a GTCS from either syncope or another non-epileptic event.[38] Serum CK can be drawn at the time of presentation and again 24 to 48 hours later. However, serum CK has low specificity and sensitivity; it may be elevated in a number of other clinical conditions, and normal postictal CK levels do not exclude epilepsy.[38][39]
EEG
All patients with a suspected seizure should have an EEG performed, except perhaps for patients with previously characterised epilepsy who have one of their habitual seizures.[40][41] Other indications for EEG include worsening seizure control, patients who have recently switched medication, and unknown epilepsy type.
During an actual seizure, EEG can be used to diagnose and localise ongoing seizure activity. During a GTCS, the EEG should demonstrate bihemispheric, synchronous epileptiform activity, although the quality of the study is often obscured by movement and muscle artifact. It is much more common to have an EEG performed after a seizure has terminated. Immediately after the event, it is likely that the EEG will demonstrate diffuse slowing of background activity, with loss of normal architecture and dampened reactivity. In the case of focal to bilateral tonic-clonic seizures, there may be some asymmetry noted in the EEG, with increased suppression and slowing over the hemisphere where the seizure originated.
Long-term video-EEG monitoring (telemetry) may occasionally be required to distinguish epileptic seizures from conditions associated with intermittent symptoms attributable to non-epileptic mechanisms.[42][43]
Brain imaging
Brain imaging is indicated after any unprovoked seizure event to evaluate for possible structural lesion. The choice of brain imaging modality depends on the clinical context.
Head computed tomography (CT): this should be performed urgently if the patient has focal neurological deficits on examination or is not recovering to baseline following a seizure. In an emergency setting, the CT scan is more easily obtained than magnetic resonance imaging (MRI) and can provide information about mass lesions, haemorrhage, infarctions, or infections that provoked a seizure.[44] In a patient who has returned to baseline and has a normal neurological examination, the utility of a head CT is limited.
MRI of the brain: this is the standard imaging test for a patient who has returned to baseline and has a normal neurological examination. Unless contraindicated, all patients with an unprovoked seizure event should have an MRI scan with and without gadolinium contrast within 1 month of the event. A 3 Tesla MRI (if available) is a more sensitive measure than head CT for detecting abnormalities such as cortical dysplasia, migrational defects, or small neoplasms, and can be used to better characterise other larger lesions.[44][45][46]
Functional MRI may be used for pre-surgical mapping.[47]
Imaging results are usually normal for generalised-onset epilepsy; a variety of lesions may be identified in patients with focal-onset epilepsy.
How to take a venous blood sample from the antecubital fossa using a vacuum needle.
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