Seizure Disorders

Core concept: Epileptic seizures reflect transient abnormal neuronal activity; a single acute symptomatic or provoked seizure does not automatically establish epilepsy.

Key clinical distinction: Classify seizure type and distinguish acute symptomatic seizures and mimics before selecting long-term antiseizure treatment.

Clinical priority: Convulsive status epilepticus requires urgent stabilization, prompt benzodiazepine treatment, and escalation if seizures persist.

Etiology and Clinical Context

Definition and causes

A seizure is a transient clinical manifestation of abnormal excessive or synchronous neuronal activity. Epilepsy describes an enduring predisposition to unprovoked seizures, not every isolated provoked event. Structural lesions, genetic channel or network abnormalities, immune or infectious disease, metabolic disturbances, and toxic or medication-related factors contribute (Shakkottai & Lomen-Hoerth, 2019).

Epidemiologic context and interpretation

Epilepsy may arise across the lifespan (Shakkottai & Lomen-Hoerth, 2019). Children, older adults, patients with a previous brain injury, and individuals with certain inherited syndromes differ in seizure etiology and recurrence risk. An acute symptomatic seizure during severe metabolic disturbance is counted and managed differently from unprovoked recurrent seizures. Epidemiologic estimates must therefore use a clearly defined population and case definition.

Pathophysiology

Neurophysiologic mechanisms

Neuronal excitability reflects a balance among glutamatergic excitation, GABA-mediated inhibition, intrinsic sodium, potassium and calcium conductances, and network connectivity. Reduced inhibition or enhanced excitation may promote pathologic discharges. Focal seizures originate in a network in one hemisphere; generalized seizures engage bilateral networks from onset. A seizure can propagate and alter awareness or motor behavior (Shakkottai & Lomen-Hoerth, 2019).

Clinical Manifestations

Features include stereotyped sensory, autonomic, behavioral, or motor phenomena; changes in consciousness (awareness and responsiveness); tonic or clonic activity; and postictal confusion or focal deficits (Shakkottai & Lomen-Hoerth, 2019). Focal seizures with impaired consciousness may have automatisms. Distinguish syncope, psychogenic nonepileptic events, movement disorders, migraine aura, and transient ischemic attack. Status epilepticus is a time-critical emergency and may occur without dramatic motor activity. Clinical descriptions should use the 2025 ILAE terminology for consciousness and event sequence (Beniczky et al., 2025).

2025 ILAE seizure classification: terminology and clinical application

The 2025 ILAE classification distinguishes four principal classes (focal, generalized, unknown whether focal or generalized, and unclassified) from clinical descriptors (Beniczky et al., 2025; International League Against Epilepsy [ILAE], 2025). In focal seizures, “consciousness” replaces “awareness” as a classifier, incorporating both awareness and responsiveness. The older motor/nonmotor split is replaced by observable versus nonobservable manifestations, and the time sequence of signs should be documented. Terminology in older textbooks may therefore differ even when their explanations of cortical excitability remain valid (Beniczky et al., 2025).

Do not label a witnessed event as generalized simply because the first observed manifestation was bilateral tonic–clonic activity: a focal seizure may evolve to bilateral convulsive activity. When onset cannot be reliably determined, document uncertainty, obtain detailed witness history and EEG as appropriate, and avoid prematurely selecting narrow-spectrum therapy on an assumed seizure class (Beniczky et al., 2025).

Diagnostic Evaluation

Obtain witness descriptions, precise chronology, provoking factors, medication history, glucose/electrolyte evaluation when indicated, and a focused neurologic examination (Shakkottai & Lomen-Hoerth, 2019). EEG can show epileptiform activity but a normal routine EEG does not exclude epilepsy. MRI is important for suspected structural causes. Classification and recurrence risk guide long-term treatment decisions.

Diagnosing epilepsy: recurrence and the clinical meaning of EEG

An acute symptomatic seizure provoked by a contemporaneous metabolic, toxic, infectious, or structural insult is not automatically epilepsy (Shakkottai & Lomen-Hoerth, 2019). Epilepsy may be diagnosed after recurrent unprovoked seizures, after one unprovoked seizure with sufficiently high expected recurrence risk, or with an identified epilepsy syndrome under accepted operational definitions. A concordant structural lesion, epileptiform EEG, or remote neurologic injury may increase recurrence risk. A normal routine EEG has limited sensitivity and cannot exclude a convincing witnessed seizure; integrate event semiology, timing, medical context, imaging, and specialist assessment.

A new-onset event with fever, severe headache, persistent focal deficit, immunosuppression, pregnancy-related risk, or failure to return to baseline changes the urgent workup. Additional EEG monitoring can be needed when episodes remain unexplained or nonconvulsive status is possible. Video-EEG correlation is especially valuable when the differential includes functional nonepileptic seizures or more than one event type. Longitudinal counseling should cover injury risk, driving restrictions under applicable laws, treatment adherence, and rescue planning (Tesoro et al., 2026).

Differential Diagnosis

Key mimics and evaluation constraints

Syncope may include brief convulsive movements and should not be assumed to represent epilepsy (Shakkottai & Lomen-Hoerth, 2019). Clues include a prodrome, positional triggers, pallor, and rapid return to baseline, while prolonged postictal confusion favors an epileptic event. Psychogenic nonepileptic seizures are genuine, involuntary events requiring a respectful diagnostic approach; a definitive distinction may require capturing a typical event with video-EEG when clinically appropriate. Consider metabolic derangements, intoxication or withdrawal, acute intracranial pathology, infection, and medication-related threshold changes. A normal interictal EEG cannot exclude epilepsy; EEG abnormalities must also be interpreted in clinical context.

Treatment and Management

Treatment rationale

Antiseizure drugs modify excitability or synaptic transmission through sodium-channel modulation, increased inhibitory signaling, or other mechanisms; choice depends on seizure type, comorbidity, interactions, and reproductive considerations (Shakkottai & Lomen-Hoerth, 2019). Acute prolonged convulsive seizures warrant emergency protocol-based therapy. For drug-resistant focal epilepsy, consider comprehensive epilepsy-center evaluation for surgery, neurostimulation, or specialized therapies.

Syndromic differentiation and mechanism-matched pharmacology

Focal seizures with preserved consciousness may begin with asymmetric sensory symptoms, automatisms, autonomic aura, or unilateral rhythmic movements while the patient remains aware (Shakkottai & Lomen-Hoerth, 2019). Focal seizures with impaired consciousness can include behavioral arrest and impaired responsiveness. Generalized absence seizures produce brief lapses with abrupt onset/offset and characteristic EEG patterns; myoclonic seizures are brief shock-like jerks; atonic seizures abruptly reduce tone, increasing injury risk. Medication suitability depends on classification: a narrow-spectrum sodium-channel drug appropriate for focal seizures can worsen some generalized absence or myoclonic syndromes, while broad-spectrum options may cover several generalized phenotypes. Ethosuximide illustrates a targeted therapy for typical absence seizures; other agents have broader action on sodium channels, synaptic vesicle proteins, or GABA transmission. Contemporary prescribing must address drug interactions, pregnancy potential, mental health effects, organ function, and updated safety guidance.

Electroclinical syndromes and seizure-type medication traps

Typical absence seizures cause brief, abrupt interruption of activity, usually without a prolonged postictal state; a generalized approximately 3-Hz spike-and-wave EEG pattern is a classic teaching clue (Shakkottai & Lomen-Hoerth, 2019). Generalized myoclonic seizures involve brief shock-like jerks, often prominent after awakening in some genetic generalized epilepsies; generalized polyspike-wave activity may provide supporting evidence. Focal temporal seizures can include an experiential aura, automatisms, and impaired awareness with possible temporal epileptiform findings. Structural focal epilepsy may show concordant MRI and EEG abnormalities, but discordance is common enough to require caution.

Treatment cannot be chosen by the presence of shaking alone. Ethosuximide is associated with typical absence seizures; antiseizure drugs predominantly selected for focal disease may aggravate certain generalized absence or myoclonic syndromes. Broad-spectrum agents may be appropriate for several generalized types, but renal/hepatic function, mental health effects, interactions, teratogenicity, pregnancy potential, and patient goals strongly influence selection. As an example, a patient with morning myoclonic jerks and later generalized convulsions should not automatically receive a narrow-spectrum focal-seizure drug solely because the witnessed convulsion appeared asymmetric (Shakkottai & Lomen-Hoerth, 2019).

Complications and Red Flags

Status epilepticus: physiologic injury and urgent treatment

Convulsive activity lasting approximately five minutes, or recurrent seizures without recovery, requires prompt management as status epilepticus. Increased metabolic demand, excitotoxicity, hypoventilation, aspiration, temperature dysregulation, and circulatory complications amplify injury. Stabilize the airway and circulation, check bedside glucose, correct identifiable precipitants, and administer an appropriate first-line benzodiazepine without waiting for imaging or routine EEG. Persistent seizures warrant protocol-based second-line antiseizure therapy, specialist escalation, and continuous EEG when nonconvulsive status or persistent encephalopathy is suspected. Refractory status epilepticus requires coordinated intensive-care management (Tesoro et al., 2026).

Benzodiazepine-refractory convulsive status: comparative evidence

Convulsive status epilepticus is a time-sensitive emergency. Following an adequate first-line benzodiazepine, prompt loading with an appropriate second-line antiseizure medication is required. The ESETT randomized trial found similar rates of its 60-minute composite outcome for levetiracetam (47%), fosphenytoin (45%), and valproate (46%) in benzodiazepine-refractory convulsive status epilepticus. This does not establish that the three agents are interchangeable in every patient: pregnancy potential, liver disease, hypotension/arrhythmia, interactions, contraindications, and institutional protocols affect selection. Continued altered consciousness requires consideration of EEG for nonconvulsive status (Kapur et al., 2019).

Clinical Reasoning Priorities

Applied case: classify before selecting treatment

A young adult reports abrupt morning arm jerks followed occasionally by bilateral convulsions, especially after sleep deprivation. Labeling this only as tonic-clonic epilepsy misses a possible generalized syndrome with myoclonic features and could produce inappropriate medication selection. Obtain an event timeline and EEG, and evaluate the overall syndrome rather than applying focal-onset treatment by default. A separate patient who has one seizure during profound hyponatremia requires correction of the provoking disorder and individualized recurrence assessment; the event alone does not establish chronic epilepsy (Beniczky et al., 2025; Shakkottai & Lomen-Hoerth, 2019).

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References

Beniczky, S., Trinka, E., Wirrell, E., Abdulla, F., Al Baradie, R., Alonso Vanegas, M., Auvin, S., Bhushan Singh, M., Blumenfeld, H., Bogacz Fressola, A., Caraballo, R., Carreno, M., Cendes, F., Charway, A., Cook, M., Craiu, D., Ezeala-Adikaibe, B., Frauscher, B., French, J., . . . Cross, J. H. (2025). Updated classification of epileptic seizures: Position paper of the International League Against Epilepsy. Epilepsia, 66(6), 1804–1823. https://doi.org/10.1111/epi.18338

International League Against Epilepsy. (2025, April 23). Updated classification of epileptic seizures (2025). https://www.ilae.org/updated-classification-epileptic-seizures-2025

Kapur, J., Elm, J., Chamberlain, J. M., Barsan, W., Cloyd, J., Lowenstein, D., Shinnar, S., Conwit, R., Meinzer, C., Cock, H., Fountain, N., Connor, J. T., Silbergleit, R., & NETT and PECARN Investigators. (2019). Randomized trial of three anticonvulsant medications for status epilepticus. The New England Journal of Medicine, 381(22), 2103–2113. https://doi.org/10.1056/NEJMoa1905795

Shakkottai, V. G., & Lomen-Hoerth, C. (2019). Nervous system disorders. In G. D. Hammer & S. J. McPhee (Eds.), Pathophysiology of disease: An introduction to clinical medicine (8th ed.). McGraw-Hill Education.

Tesoro, E. P., Almohaish, S., & Brophy, G. M. (2026). Status epilepticus. In M. A. Chisholm-Burns, P. M. Malone, J. M. Kolesar, K. C. Lee, P. B. Bookstaver, & K. R. Matthias (Eds.), Pharmacotherapy principles & practice (7th ed.). McGraw Hill.