How is a seizure diagnosed in a patient with unclear symptoms and potential underlying neurological conditions, such as epilepsy?

Diagnosing Seizures When the Presentation is Unclear

When seizure diagnosis is uncertain, prioritize a detailed eyewitness account of the event focusing on specific clinical features that distinguish seizures from syncope, followed by targeted EEG and neuroimaging based on clinical suspicion. 1

Critical Historical Features to Establish Diagnosis

The diagnosis hinges on obtaining specific details about the event itself, particularly from eyewitnesses:

Features Strongly Suggesting Seizure (Not Syncope)

• Timing and duration of movements: Tonic-clonic movements lasting >1 minute that begin simultaneously with loss of consciousness indicate seizure, whereas movements in syncope last only seconds and occur after unconsciousness begins 1

• Character of movements: Coarse, rhythmic, synchronous jerking movements suggest epilepsy, while asynchronous, small, non-rhythmic jerks suggest syncope 1

• Tongue biting location: Lateral tongue biting is highly specific for seizure, whereas tip-of-tongue biting occurs in syncope 1

• Aura characteristics: A rising epigastric sensation or unusual unpleasant smell suggests epilepsy 1

• Post-event confusion: Prolonged confusion (>several minutes) with aching muscles strongly suggests seizure, whereas immediate clear-headedness indicates syncope 1, 2

Features Suggesting Syncope (Not Seizure)

• Triggers: Syncope is usually triggered by specific circumstances (prolonged standing, emotional stress, pain), whereas epilepsy rarely has clear triggers 1

• Pre-event symptoms: Nausea, vomiting, lightheadedness, visual blurring, cold sweating, and abdominal discomfort suggest syncope 1

• Pallor and sweating: These are uncommon in epilepsy but typical of syncope 1

Diagnostic Testing Algorithm

When to Order EEG

• EEG is recommended when epilepsy is the likely cause or when clinical data are equivocal 1

• EEG should be performed within 24 hours after a suspected seizure, particularly in children 3

• If the initial waking EEG is normal, obtain a sleep EEG as it increases diagnostic yield 3

• A normal interictal EEG cannot rule out epilepsy—it must be interpreted in clinical context 1

• When diagnostic uncertainty persists, tilt-table testing with continuous EEG monitoring can distinguish convulsive syncope from epilepsy by demonstrating hemodynamic changes (hypotension/bradycardia) during the event with normal EEG 1

When to Order Neuroimaging

• CT scan is essential for all adults with first seizure to identify structural lesions 4

• Emergent neuroimaging is required for patients with persistent focal deficits or failure to return to baseline within several hours 4

• MRI is preferred over CT as part of comprehensive diagnostic assessment (though not necessarily emergent) to identify subtle structural abnormalities including malformations of cortical development 3

• Brain imaging should be avoided in uncomplicated syncope unless neurological evaluation indicates otherwise 1

Laboratory Evaluation

• All patients with first seizures require comprehensive metabolic evaluation including complete blood count, comprehensive metabolic panel, as approximately 8% have correctable metabolic abnormalities 2, 4

• Specific attention to: glucose, sodium, calcium, magnesium, and renal function 4, 5

• Toxicology screen when circumstances suggest toxic ingestion 2, 4

• Elevated prolactin levels 10-20 minutes after the event help differentiate generalized tonic-clonic or partial seizures from psychogenic nonepileptic seizures 3

Special Diagnostic Scenarios

Distinguishing Convulsive Syncope from Epilepsy

When history cannot clearly determine whether convulsive movements were secondary to syncope:

• Tilt-table testing is reasonable to distinguish convulsive syncope from epilepsy in selected patients 1

• Approximately 50% of patients with questionable or drug-refractory epilepsy have positive tilt-table tests suggestive of vasovagal etiology 1

• During tilt-table testing, convulsive movements associated with hypotension and bradycardia confirm vasovagal syncope rather than epilepsy 1

Identifying Psychogenic Pseudoseizure

• Apparent unconsciousness with loss of motor control combined with normal blood pressure, heart rate, and EEG during tilt-table testing rules out true syncope and most forms of epilepsy 1

• Eye closure during the event, long periods of apparent unconsciousness, and increased (rather than decreased) heart rate and blood pressure are highly specific for pseudosyncope 1

Common Diagnostic Pitfalls

• Eyewitnesses may incorrectly report movements—synchronous jerks can occur in syncope, and brief myoclonic jerks in syncope may be misinterpreted as seizure activity 1

• Urinary incontinence occurs in both seizures and syncope and should not be used as a distinguishing feature 1

• Fatigue after reflex syncope may be confused with postictal state—the key distinction is duration and severity of confusion 1

• When uncertain, it is better to postpone the diagnosis of epilepsy than to falsely diagnose it, given the significant psychosocial implications of an epilepsy diagnosis 1

• History and physical examination predict most metabolic abnormalities except occasional cases of hypoglycemia and subdural hematomas 4

Risk Stratification for True Seizure

High-risk features suggesting true unprovoked seizure with increased recurrence risk include:

• History of prior brain insult 2
• Epileptiform abnormalities on EEG 2
• Structural lesion on neuroimaging 2
• Focal neurologic examination findings (97% correlation with symptomatic seizures) 4
• Fever (warrants strong consideration of CNS infection) 4