Seizure: What is it and Why do We Study it?
The terms ‘seizure’, ‘convulsion’ and ‘fit’ are often used both interchangeably and incorrectly.
- A seizure is an episode of abnormal neurological function caused by an abnormal electrical discharge of brain neurons. The seizure is also referred to as an ictus or ictal period.
- A convulsion is an episode of excessive and abnormal motor activity. Seizures can occur without convulsions, and convulsions can be caused by other conditions.
- The term ‘fit’ is best avoided in medical terminology, but is a useful term for non-medical personnel.
Seizures are common. It has been estimated that up to 10% of the population will have at least one seizure in their lifetime, and 1–3% of the population will develop epilepsy. A single seizure may be a reaction to an underlying disorder, part of an established epileptic disorder, or an isolated event with no associated pathology. The challenge is to rapidly identify and treat life-threatening conditions as well as to identify benign conditions that require no further investigation or treatment.
The manifestations of epileptic disorders are extremely varied. Two international classifications have been developed: the International Classification of Epileptic Seizures, and the International Classification of Epilepsy and Epileptic Syndromes. The former divides epileptic seizures into two major categories: partial and generalized.
- Partial Epileptic
Partial epileptic seizures are further classified according to the impairment or the preservation of consciousness into simple partial and complex partial seizures. Either condition may secondarily generalize into tonic-clonic seizures.
- Generalized Seizures
Generalized seizures can be divided into convulsive and non-convulsive types.
Convulsive seizures are generalized tonic-clonic seizures or grand mal seizures.
Non-convulsive generalized seizures include absence seizures (previously termed petit mal seizures), myoclonic, tonic and atonic seizures.
Under the International Classification, epilepsy and epileptic syndromes are initially classified according to their corresponding types of seizures into localization related and generalized disorders. Each disorder can be further classified according to its relationship to aetiological or predisposing factors into symptomatic, cryptogenic or idiopathic types.
Different seizure types are associated with differing aetiological and prognostic factors. The details of the classification systems are not as important in emergency medicine as the concept of recognizing the different seizure types and being aware of the accepted terminology when discussing and referring cases.
Given the high frequency of this condition in emergency departments (ED) it is important to have a management strategy formulated in advance. One such approach has been developed by the American College of Emergency Physicians. The four main management concepts are as follows:
- Altered mental state should be thoroughly assessed and not assumed to be due to a post-ictal state.
- Patients with known epilepsy who have recovered completely from a typical seizure require little further investigation. If they remain obtunded or have atypical features they must be fully evaluated, e.g., biochemical analysis, CT scan, etc.
- Patients with epilepsy should be encouraged to seek continuing care.
- Patients at risk of recurrent seizures should be advised about situations of increased personal risk, such as driving, operating power machinery or swimming alone.
A generalized convulsion is a dramatic event. Patients and those accompanying them will often be frightened, anxious and concerned, not only for the acute event but for what is may signify.
A diagnosis of epilepsy carries important implications. The patient’s occupation, social activities, ability to drive a car and long-term health implications may all be profoundly influenced. It is therefore vital that the diagnosis is correct and explained fully to the patient and relatives.
The majority of patients will have completed the seizure before arrival in the ED. Patients still seizing are treated immediately according to the guidelines below for status epilepticus.
The first and most important task is to determine whether a seizure has occurred. As the majority of patients will have returned to normal by the time they are reviewed in the ED, the diagnosis is made primarily on history.
Patients will not remember seizures other than simple and partial seizures, and the reports of witnesses may be unreliable or inconsistent. With the exception of partial seizures, generalized seizures are not accompanied by an aura.
Most seizures last less than 2 minutes, are associated with impaired consciousness, loss of memory for the event, purposeless movements, and a period of post-ictal confusion.
Although witnesses may grossly overestimate the duration, prolonged seizures, those occurring in association with a strong emotional event and those with full recall of events, should be regarded with suspicion.
Similarly, motor activity that is coordinated and not bilateral, such as side-to-side head movements, pelvic thrusting, directed violence and movement that changes in response to external cues, are less likely to be true seizures.
Conditions such as syncope Opens in new window may be accompanied by myoclonic activity and are important to distinguish from true seizures.
Migraine Opens in new window, transient ischaemic attacks, hyperventilation episodes and vertigo are all important conditions to consider in the differential diagnosis. Pseudoseizures is discussed here Opens in new window.
The history, examination and investigation process is aimed at identifying associated conditions and treatable causes of seizures.
The aetiology of seizures can be classified into five groups on the basis:
- Acute symptomatic — Occuring during an acute illness with a known central nervous system insult.
- Remote symptomatic — Occuring without provocation in a patient with a prior central nervous system insult known to be associated with an increased risk of seizures, e.g. encephalopathy, meningitis, head trauma or stroke.
- Progressive encephalopathy — Occuring in association with a progressive neurological disease, e.g., neuro-degenerative diseases, neurocutaneous syndromes and malignancies not in remission.
- Febrile — Patients whose sole provocation is fever. This is almost exclusively confined to children, and as such is beyond the scope of this entry.
- Idiopathic — Patients who present de novo, or during the course of their illness, in the absence of an acute precipitating central nervous system insult. This is probably the most common group; however, this classification is by exclusion of the other causes.
A careful history is needed to decide whether this is part of an ongoing process or an isolated event. Patients may not recall previous events, may not recognize their significance, or may even avoid reporting previous episodes for fear of being labeled ‘epileptic’, with the associated consequences.
Particular attention should be paid to any history of unexplained injuries, especially when they occur during blackouts or during sleep.
Any history of childhood seizures, isolated myoclonic jerks and a positive family history increases the likelihood of epilepsy. A complete physical and neurological examination is mandatory.
Evidence of alcohol and drug ingestion and head trauma is particularly important. A comprehensive medication history may include agents known to reduce the seizure threshold in susceptible individuals, e.g. tramadol, selective serotonin reuptake inhibitors.
A careful mental state examination Opens in new window in seemingly alert patients may reveal evidence of a resolving post-ictal state or of underlying encephalopathy. All patients not fully alert should not be assumed to simply be in a post-ictal state until other causes are excluded.
Of particular importance is any evidence of underlying illness, such as fever, nuchal rigidity (meningitis) or cardiac murmurs (endocarditis). Needle tracks, evidence of chronic liver disease, dysmorphic features and marks such as café-au-lait spots (neurofibromatosis) are important aetiological clues.
Complications such as tongue biting, broken teeth and peripheral injuries are not uncommon in generalized seizures. Stress fractures can occur, particularly in the elderly, and posterior dislocation of the shoulder is an uncommon but significant and easily overlooked finding.
The investigations necessary following an uncomplicated seizure are minimal. Although it is common practice to order a variety of tests, such as electrolytes, blood sugar level and full blood count, these are rarely of benefit in the fully recovered patient.
Elevated neutrophil counts in blood and CSF may be seen as a result of a generalized seizure in the absence of an infectious disorder. Although electrolyte abnormalities may cause seizures they are unlikely to be the cause if the patient has recovered.
A serum prolactin level at 20 and 60 minutes post seizure may be helpful if the diagnosis is in doubt.
Patients with an abnormal physical or neurological examination should be managed according to clinical findings and the results of laboratory and radiological investigations. Finding suggestive of meningitis, encephalitis or subarachnoid haemorrhage are indications for cranial CT scan and lumbar puncture.
There are no clear guidelines to the routine need for or urgency of neuroimaging following a single uncomplicated seizure. Patients with focal neurological signs, those who do not recover to a normal examination, and those with a history of head trauma or intracranial pathology should all undergo cranial CT as soon as possible.
The dilemma arises in patients with complete recovery and no focal signs. The incidence of abnormalities on CT in this group of patients is less than 1%.
The decision as to whether and when to scan patients in this group will be determines largely by local factors. Generally, a contrast CT (more sensitive for subtle lesions) is performed on an outpatient basis prior to review. MRI is more sensitive than CT for infarcts, tumors, inflammatory lesions and vascular lesions, but cost and availability limit its use as a primary investigative modality.
Electroencephalography (EEG) at the time of a seizure will make a definitive diagnosis. It is not usually performed in the acute setting except when non-convulsive activity is suspected. Typically, an EEG is obtained electively on an outpatient basis, when it may still indicate an underlying focus of activity and may be able to detect specific conditions.
Once a diagnosis of first seizure is made and intercurrent conditions are excluded or treated, the patient may be discharged home. In most cases no treatment is needed.
It must be stressed to the patient that a diagnosis of epilepsy has not been made but is being considered. When the suspicion is reasonable the patient should be given the same precautionary advice as epileptic patients with regard to driving and other activities that may place them or others at risk.
The planning of investigation and follow-up for patients suspected of having a first seizure is best done in conjunction with a neurology service. Planning and consultation will ensure that appropriate investigations are completed in a timely fashion. Generallty, an inter-ictal EEG and contrast CT are completed prior to review.
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