How do you differentiate between seizure episodes, particularly absence seizures and seizures with loss of tone, and psychiatric or ENT (Ear, Nose, and Throat) causes, especially when associated with vertigo?

Differentiating Seizures from Syncope, Psychiatric, and ENT Causes

The key to distinguishing absence seizures and atonic seizures from other causes lies in the timing and characteristics of consciousness loss: absence seizures feature brief (seconds) episodes with sudden onset/termination and 3-4Hz spike-wave on EEG, while syncope presents with prodromal symptoms (nausea, lightheadedness) and brief post-ictal confusion, psychiatric causes show normal EEG during episodes, and vertiginous epilepsy typically involves temporal lobe abnormalities with very brief (<30 seconds) isolated episodes. 1, 2, 3

Distinguishing Absence Seizures from Other Causes

Clinical Features of Absence Seizures

• Duration and onset: Absence seizures are characteristically brief (lasting only seconds), with sudden onset and abrupt termination, unlike syncope which has a more gradual onset with prodromal symptoms 1, 3
• Consciousness impairment: The impairment can range from severe to inconspicuous, often accompanied by subtle motor manifestations like eyelid myoclonia (most common facial manifestation) or perioral myoclonia 3, 4
• Triggering factors: Approximately 90% of untreated patients with absence seizures can be triggered by hyperventilation, which is a critical diagnostic maneuver 3
• Post-event state: Patients typically return to baseline immediately after absence seizures, whereas syncope patients may have brief confusion but usually achieve clearheadedness quickly 1

EEG Findings

• Ictal pattern: The hallmark is generalized 3-4Hz spike/polyspike and slow wave discharges during the event 3
• Interictal findings: EEGs are normal in syncope but may show epileptiform abnormalities in seizure disorders 1
• Diagnostic value: Video-EEG monitoring during tilt-table testing can definitively distinguish among syncope, pseudosyncope, and epilepsy by capturing the characteristic patterns 1

Differentiating Atonic Seizures (Loss of Tone) from Syncope

Key Distinguishing Features

Timing of motor phenomena:

• In seizures: Tonic-clonic movements are prolonged and their onset coincides with loss of consciousness 1
• In syncope: Any tonic movements are brief (<15 seconds) and start after loss of consciousness 1

Associated symptoms before the event:

• Seizures: Aura symptoms such as unusual smells (epigastric aura), rising abdominal sensation 1
• Syncope: Nausea, vomiting, abdominal discomfort, cold sweating, lightheadedness, blurred vision 1

Post-event recovery:

• Seizures: Prolonged confusion, aching muscles, elevated creatinine kinase and prolactin 1
• Syncope: Brief or immediate return to clearheadedness, possible nausea/vomiting, pallor 1

Specific physical signs:

• Tongue biting on the side of tongue strongly suggests seizure (tip biting can occur in syncope) 1
• Blue face during the event suggests seizure 1
• Hemilateral clonic movements indicate seizure 1

Psychiatric Differential Diagnosis

Psychogenic Pseudosyncope/Pseudoseizures

• EEG findings: Normal EEG during the episode is characteristic of psychogenic events, distinguishing them from both seizures and syncope 1
• Video-EEG monitoring: Simultaneous EEG and hemodynamic monitoring during tilt-table testing shows normal EEG in pseudosyncope, diffuse slowing with delta waves in syncope, and epileptiform discharges in seizures 1
• Clinical context: Psychiatric disorders may coexist with vestibular symptoms, but a positive psychiatric history before onset is a strong predictor for somatoform presentations 5

Important Caveats

• Absence seizures in adults are frequently misdiagnosed as complex partial seizures or psychiatric conditions, particularly when manifestations are subtle 4
• Focal EEG abnormalities in absence seizure patients might be erroneously interpreted as indicating partial seizures 4
• When uncertain about epilepsy diagnosis, it is better to postpone the diagnosis than to falsely diagnose it, given the significant treatment and psychosocial implications 6

ENT Causes: Vertiginous Epilepsy vs. Peripheral Vestibular Disorders

Epileptic Vertigo Characteristics

• Duration: Isolated epileptic vertigo is typically very brief (<30 seconds) in 69.6% of cases, whereas non-isolated epileptic vertigo lasts longer (only 6.9% <30 seconds) 7
• EEG localization: Epileptic vertigo shows high-voltage spike or spike-slow-wave complexes most frequently in the temporal region (79.8%), more often left than right 8, 7
• Associated features: Auditory hallucinations may precede epileptic vertigo, and some patients experience true rotational vertigo with nausea or hearing loss 8

Vestibular Testing in Epileptic Vertigo

• Abnormal findings: Video head impulse testing (vHIT) and cervical vestibular evoked myogenic potential (cVEMP) may show abnormal responses bilaterally or unilaterally in epileptic vertigo patients 8
• Correlation with EEG: The side of absent cVEMP response may correspond to the side of epileptiform pathology on EEG, supporting brainstem involvement 8
• Prevalence: Non-isolated epileptic vertigo (8.5%) is much more common than isolated epileptic vertigo (0.8%) among patients with vestibular symptoms 7

Peripheral Vestibular Disorders (Ménière's Disease, BPPV, Vestibular Neuritis)

• Duration: Episodes typically last longer than epileptic vertigo, with Ménière's attacks lasting minutes to hours 5
• EEG findings: Normal interictal and ictal EEG distinguishes peripheral vestibular disorders from epileptic vertigo 8
• Psychiatric comorbidity: Patients with vestibular migraine show significantly higher rates of psychiatric disorders over time, while BPPV, vestibular neuritis, and Ménière's disease do not 5

Diagnostic Algorithm

Initial Assessment

1. Detailed witness account: Focus on timing of motor phenomena relative to consciousness loss, duration of episode, and post-event state 1
2. Hyperventilation provocation: Perform in suspected absence seizures (triggers 90% of cases) 3
3. Neurological examination: Look for focal deficits that would suggest structural lesions requiring imaging 1

When to Order EEG

• Indicated: When epilepsy is the likely cause, clinical data are equivocal, or nonconvulsive status epilepticus is suspected 1
• Not routinely indicated: When syncope is the most likely diagnosis 1
• Video-EEG with tilt-table: Consider when differentiation between syncope, pseudosyncope, and epilepsy remains unclear after initial evaluation 1

Neuroimaging Decisions

• MRI not routinely indicated: For neurologically normal patients with typical generalized seizures (only 2-6% yield) 1, 2
• CT/MRI not recommended: For uncomplicated syncope without focal neurological findings or head injury 1
• Carotid imaging not useful: Syncope results from global cerebral hypoperfusion, not unilateral ischemia 1

Common Pitfalls to Avoid

• Do not order extensive neurological testing (EEG, CT, MRI, carotid ultrasound) for straightforward syncope cases, as diagnostic yield is extremely low (0.24-1%) 1
• Recognize that urinary incontinence occurs in both seizures and syncope and is not discriminatory 1
• Be aware that very brief vestibular symptoms (<30 seconds) should raise suspicion for epileptic vertigo rather than peripheral vestibular disorders 7
• Remember that psychiatric history before vestibular symptom onset is a strong predictor for somatoform presentations, particularly in vestibular migraine 5