Diagnosis and Classification of Seizures and Epilepsy

This chapter includes an accompanying lecture presentation that has been prepared by the authors: .

Key Concepts

Provoked or acute symptomatic seizures are seen in up to 10% of the population. Morbidity and mortality are determined by the underlying insult. Long-term antiepileptic medication is typically not indicated and can worsen cognitive outcome.
At least one unprovoked seizure is a prerequisite to diagnose epilepsy, which is defined as an enduring predisposition for unprovoked seizures (>60% recurrence risk over the next 10 years). Epileptiform abnormalities on EEG or an epileptogenic lesion on MRI invoke a diagnosis of epilepsy after a first unprovoked seizure.
In selected patients who present with new-onset lesional epilepsy (e.g., developmental tumors, cavernous malformations), early surgery should be considered. A presurgical epilepsy evaluation should, at minimum, confirm that the event was indeed a seizure, verify that the semiology and EEG are consistent with the location of the lesion, and aid in planning the extent of resection to remove the epileptogenic zone sparing functional cortex.
The most recent epilepsy classification is guided by our advanced understanding of epilepsy etiology and comorbidities. The classification introduces five dimensions: seizure type, epilepsy type and location of epileptogenic zone, epilepsy syndrome (if present), etiology, and comorbidities.
The etiology of epilepsy can be divided into six categories: structural, metabolic, genetic, infectious, immune, and unknown causes.
A semiologic seizure classification (SSC) is used in many epilepsy surgery centers, communicating effectively the localizing information obtained from the seizure evaluation and allowing clinicians to define the semiologic zone as precisely as possible.

Seizures and epilepsy are among the most commonly seen neurological disorders. Close to 10% of the population will have a seizure during their lifetime, and many of them are related to acute symptomatic causes and other triggers. ^, After a first unprovoked seizure, one-third of patients will develop epilepsy, which has a lifetime prevalence of 2% to 3%. ^,

Neurosurgical conditions are among the most common causes of both acute symptomatic seizures and focal epilepsy. An acute symptomatic seizure from trauma or stroke may require expedient intervention and in some patients temporary antiepileptic medications. On the other hand, patients with a first unprovoked seizure and a remote symptomatic or asymptomatic lesion on MRI (e.g., a low- or high-grade glioma or cavernous malformation) have de facto epilepsy and may require surgical intervention to address the underlying structural abnormality and hopefully also cure the epilepsy.

Seizures are challenging to diagnose for several reasons, including the difficulties in obtaining an accurate and complete history and the numerous disorders that mimic seizures. Interictal EEG can be normal, even in patients with epilepsy, and event capture with video EEG can be elusive if the events are infrequent. MRI abnormalities may not necessarily be related to the seizure or may not be readily detected on imaging.

In this chapter, we present a practical approach to the diagnosis and classification of seizures and epilepsy with a focus on neurosurgical aspects.

Approach to New-Onset Seizure

Initial Diagnostic Approach and Differential Diagnosis

The approach to a patient presenting with a first-time event that is concerning for a seizure is guided by the following questions:

Was the event a seizure?
Was the seizure provoked or unprovoked?
Does the patient have epilepsy and what type?

Was the Event a Seizure?

It is essential to consider the differential diagnosis when a patient presents with a first-time event that is concerning for a seizure. Other diagnostic considerations include syncope, transient ischemic attacks, migraine auras, paroxysmal movement disorders, sleep disorders, panic attacks, and psychogenic nonepileptic spells (PNES). Although the differential diagnosis for a seizure is broad, oftentimes key elements of the history and physical examination can guide the diagnosis ( Table 80.1 ).

TABLE 80.1

New-Onset Seizure: Differential Diagnoses

Modified from Hirsch LJ, Pedley TA. Syncope, seizures and their mimics. In: Rowland LP, Pedley TA, eds. Merritt’s Neurology. 12th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2010:15–21.

DDx	Key History Components
Syncope	Prodrome (lightheadedness, tunnel vision, provoking factors) Duration of event (typically <15 seconds) Movements during event (myoclonus, rarely tonic posturing) Time to recovery (rapid)
Transient ischemic attack	Able to report entire event Rapid onset of negative symptoms (e.g., weakness, numbness, aphasia) Duration of event (>5 minutes) No associated abnormal movements No associated loss of awareness
Migraine	Duration of visual aura (most commonly >5 minutes) Description of headache (typically unilateral, pulsating) Progression of neurologic symptoms (prolonged) Duration of event in total may last longer than 24 hours No associated loss of awareness No abnormal movements Assess for family history of migraines
PNES	History of physical, emotional, or sexual trauma Duration of events (can last >2 minutes) Symptoms wax and wane in intensity Eyes closed Clinical features: pelvic thrusting, vocal stuttering, asymmetric shaking limbs (exclude frontal lobe epilepsy) Behaviors modifiable by the examiner

DDx, Differential diagnosis; EEG, electroencephalography; LOC, loss of consciousness; PNES, psychogenic nonepileptic spells; REM, rapid eye movement; TIA, transient ischemic attack.

History

Obtaining a reliable history regarding episodes associated with altered mental status or loss of consciousness can be challenging. Furthermore, patients may not offer diagnostic information without being asked direct questions (e.g., preceding déjà vu or epigastric aura). However, these questions are essential, and in patients who present with a lesion, concordant seizure semiology based on neuroanatomy should be included in the initial assessment ( Table 80.2 ).

TABLE 80.2

Typical Semiology by Anatomic Region

Lobe	Seizure Semiology
Frontal	Aura Olfactory Autonomic Motor Seizure Simple motor: tonic, clonic, myoclonic, asymmetric tonic, versive Hypermotor Automotor Gelastic Nonmotor Seizure Dyscognitive Aphasia, dysphasia Apractic Dialeptic
Temporal ^,	Aura Abdominal aura (rising epigastric sensation) Fear Olfactory aura (often noxious smell) Gustatory aura (often metallic taste) Auditory aura (e.g., abrupt ringing, buzzing, chirping, voices) Psychic: memory illusions (déjà vu, jamais vu); hallucinations Visual: illusions (e.g., macropsia, micropsia, blurred images) Autonomic: heart racing Motor Seizure Automotor Nonmotor Seizure Dyscognitive Dialeptic Aphasic Autonomic Seizure Apneic seizure Tachycardia; bradycardia/asystole
Insular	Aura Somatosensory (paresthesias: tingling, warmth, tension, electrical; pain) Large areas, bilateral, no Jacksonian spread Viscerosensitive (constriction, suffocation, choking); visceromotor Multimodal: early olfactory, gustatory, viscerosensory, auditory Psychic aura: anxiety, panic, fear Autonomic: dyspnea, breathlessness Nonmotor Seizures Autonomic: hypersalivation Dyscognitive/dialeptic Motor Seizures Speech apraxia Automatisms
Parietal	Aura (94%) Somatosensory auras (e.g., tingling, numbness, pain, thermal sensation) Disturbances of body image Sensation of movement of a part of the body Complex visual illusions Motor Seizures Tonic motor, focal motor (typical for supraparietal onset) Automatisms (typical for infraparietal onset) Head deviation Postictal Todd paresis Postictal dysphasia
Occipital	Aura Visual (73%) Elementary visual hallucinations (e.g., colored shapes) Flashing colors Ictal blindness (28%) Motor Seizures Uncontrollable eye movements: eye pulling, nystagmus Contralateral head and eye deviation Focal motor Automatism

A witness report is crucial with patients who present with an episode of loss of consciousness. The history should include the patient’s own account before loss of consciousness, any memory of the event, and symptoms after the event (e.g., tongue bite, time to return to baseline, awareness of the event). The lifetime prevalence of syncope is around 50%, and a misdiagnosis as a seizure can not only lead to undue restrictions for the patient but also incidental imaging findings. A typical situational trigger and prodrome of muffled sound, nausea, and a sensation that one is going to faint is often helpful to diagnose a vasovagal syncope. Witness descriptions of seizures and syncope can be challenging, particularly if the initial loss of body tone and quick recovery are not observed. A structured questionnaire may more reliably differentiate between epilepsy and syncope as well as epilepsy and PNES compared with patient-reported factors.

A detailed witness description often contributes to the physician’s understanding of the event and modifies the pretest probability of a seizure.

Symptoms at Onset of the Event

Focal symptoms such as illogical speech, automatisms, head or body version, or unilateral rhythmic shaking point toward focal epilepsy as the underlying etiology. The patient is typically not aware of these symptoms.

Description of the Event

A report of “shaking” by a witness is often not helpful. In a landmark German study, syncopal events were induced by the Valsalva maneuver. In this study, 90% of subjects had myoclonic activity, most commonly multifocal, and 79% had some posturing with head turning, lip-licking, chewing, fumbling, or gaze deviation. The typical evolution of a convulsive seizure with tonic stiffening followed by clonic activity is not seen during syncope. Eye opening is often reported with seizures, while eye closure is more likely to be associated with syncope or PNES.

Postictal Symptoms

Postictal confusion is strongly predictive of epilepsy. Quick recovery of orientation after an episode of loss of consciousness is suggestive of syncope rather than focal seizure. This can be assessed by asking patients when they subjectively felt they returned to baseline, estimating the period of postictal amnesia. If the response is in the ambulance or emergency department, the event is more likely a seizure.

Physical Examination

The diagnosis of seizures may be supported or refuted by clinical findings, some of which are outlined in the following sections.

Tongue Bite

Tongue biting can be reported in epileptic seizures, syncope, and PNES. Lateral tongue bite has been reported as 100% specific to generalized convulsions. Biting the tip of the tongue is less specific and can be seen in syncope and nonepileptic events.

Self-Injury

Injuries related to seizures (e.g., lacerations, bruises, thoracolumbar compression fractures, posterior shoulder dislocations) should be assessed. Seizure-induced injuries are most frequently minor, with contusions most commonly reported, followed by abrasions, fractures, concussions, sprains/strains, and burns. A spontaneous, unwitnessed episode of posterior shoulder dislocation is highly predictive of a seizure given the rarity otherwise and the vulnerable position of the shoulder during a convulsion. Of note, self-injury has been reported in 8% to 30% of patients with nonepileptic events. Most commonly, bruises from falls or motor activity were reported. Burns were exclusively seen in patients with epilepsy.

Incontinence

Although patients are commonly asked about incontinence, a pooled analysis of the data from the current literature has found that urinary incontinence offers no value in distinguishing between epileptic seizures, nonepileptic events, and syncope.

Skin Examination

Skin examination is helpful to asses for any signs of trauma after a seizure. Rarely, identification of a neurocutaneous syndrome (e.g., tuberous sclerosis, neurofibromatosis) can aid in the diagnosis of specific epilepsy syndromes.

Cardiac

Identification of an arrhythmia, heart murmur, bradycardia, tachycardia, or orthostatic hypotension can help elucidate the etiology, particularly if the history is equivocal for a syncopal event. It is necessary to keep in mind that seizures can present not only with tachycardia but also with bradycardia and asystole, which are associated with sudden unexplained collapse and falls not related to convulsive activity.

Was the Seizure Provoked or Unprovoked?

The initial evaluation of a patient presenting with a first seizure should categorize the event based on triggering factors and clinical features ( Box 80.1 ). ^,

BOX 80.1

First Seizure Classification

Initial Classification of New-onset Seizure Based on Underlying Cause and Type

Provoked Seizure

The seizure is caused by a provoking factor (e.g., alcohol, drugs, or metabolic derangement).

Acute Symptomatic Seizure

The seizure results from an acute symptomatic condition that occurred within <7 days (e.g., stroke, intracerebral hemorrhage, subdural hemorrhage, trauma, or infection).

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