3.3 Differentiating Epileptic vs Non-Epileptic Events

3.3 Differentiating Epileptic vs Non-Epileptic Events

Approximately 20% to 30% of patients admitted to specialized Epilepsy Monitoring Units for refractory seizures are diagnosed with non-epileptic paroxysmal events. The gold standard for definitive diagnosis is continuous long-term video-EEG monitoring (vEEG) capturing habitual clinical episodes. Misdiagnosing non-epileptic events as epilepsy leads to inappropriate antiepileptic drug (AED) polypharmacy, invasive procedures, iatrogenic intubation for 'pseudo-status epilepticus', and severe psychological distress. The CLTM technologist plays a pivotal front-line role in differentiating these conditions through rigorous observation, provocative testing, and artifact analysis.

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1. Psychogenic Non-Epileptic Seizures (PNES) / Functional Seizures

Psychogenic Non-Epileptic Seizures (PNES)—also termed Functional Seizures or Dissociative Seizures—are paroxysmal episodes of altered movement, sensation, or consciousness that resemble epileptic seizures but are not caused by abnormal cortical epileptiform discharges. They represent a subtype of Functional Neurological Disorder (FND).

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|               SEMIOLOGY: EPILEPTIC GTCS vs. FUNCTIONAL SEIZURES (PNES)        |
|                                                                               |
|   Clinical Feature          Epileptic GTCS            Functional Seizure (PNES)|
|   -----------------------   -----------------------   ------------------------|
|   Eye Status During Event   Eyes Open / Tonic Stare   Tightly Closed (Resistant|
|   Head Movements            Tonic Version / Unilateral Side-to-Side ('No-No')  |
|   Limb Motor Activity       Synchronous Clonic Decel  Asynchronous / Flailing |
|   Pelvic Movement           Rare / Minor              Pelvic Thrusting/Opistho|
|   Vocalization              Initial Ictal Cry         Sobbing, Weeping, Words |
|   Tongue Biting             Lateral Border (>95% Sp)  Tip of Tongue / Lips    |
|   Pupillary Light Reflex    Sluggish / Dilated        Preserved & Reactive    |
|   Event Duration            1 to 2 minutes            Prolonged (>15-30 min)  |
|   Ictal EEG                 Evolving Spikes & Waves   Normal Alpha + Artifact |
|   Post-Ictal EEG            Generalized Suppression   Prompt Normal Alpha PDR |
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Clinical and Semiological Hallmarks of PNES:

1. Ictal Eye Closure with Active Resistance: Prolonged ictal eye closure and resistance to eyelid opening support PNES in the appropriate context, but are not diagnostic alone (frequently demonstrating Bell's phenomenon, where eyeballs roll upward upon forced lid elevation). In true epileptic seizures, the eyes are typically wide open, fixed, staring, blinking, or tonically deviated.
2. Side-to-Side Head Rolling: Rhythmic or arrhythmic side-to-side 'no-no' shaking of the head is highly specific for non-epileptic events.
3. Asynchronous / Out-of-Phase Limb Movements: Flailing, thrashing, or bicycling of arms and legs where extremities move out of phase with alternating, waxing and waning intensity, rather than the synchronous, decelerating clonic jerking characteristic of epileptic GTCS.
4. Pelvic Thrusting & Opisthotonos: Forward pelvic thrusting and dramatic arching of the back (arc de cercle) are prominent in functional motor events.
5. Suggestibility & Modulability: Events can frequently be induced by suggestion (e.g., verbal suggestion during hyperventilation, photic stimulation, or application of a moist saline swab) and can be modified, distracted, or intensified by examiner interaction.
6. Preserved Responsiveness During Generalized Motor Activity: The patient may speak, weep, or follow commands while all four limbs are exhibiting vigorous motor movements.
7. Tongue Biting Location: Lacerations of the lateral margin of the tongue have >95% specificity for epileptic generalized tonic-clonic seizures due to forceful masseter tonic contraction. In contrast, bites to the anterior tip of the tongue or inside of the lips occur frequently in PNES or accidental falls.
8. Post-Ictal Transition: Patients with PNES often transition abruptly from violent motor thrashing to full alertness, conversation, or weeping without the stertorous breathing, severe metabolic acidosis, or profound lethargy seen after epileptic GTCS.

Electroencephalographic Criteria in PNES:

• Preserved Background Activity: Normal awake rhythms—including an intact Posterior Dominant Rhythm (PDR / alpha rhythm) and normal frontocentral beta activity—remain present immediately before, during (visible between muscle bursts), and immediately after the event.
• Artifact Analysis: Rhythmic movements produce high-amplitude muscle (EMG) and movement artifacts on EEG, but no underlying electrographic evolution in frequency, morphology, amplitude, or spatial distribution occurs.
• Absence of Post-Ictal Slowing: The immediate post-ictal EEG shows prompt reconstitution of baseline alpha rhythm without post-ictal generalized electrocerebral suppression (PGES) or diffuse delta slowing.

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2. Convulsive Syncope

Syncope is a transient loss of consciousness caused by acute, global cerebral hypoperfusion (vasovagal, orthostatic, or cardiogenic). In approximately 40% to 50% of syncopal episodes, involuntary motor movements occur (convulsive syncope), which are frequently misdiagnosed as epileptic seizures.

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|               CONVULSIVE SYNCOPE: THE 'SLOW-FLAT-SLOW' EEG PATTERN             |
|                                                                               |
|   [Normal Awake]   -->   [Hypoperfusion]  -->  [Max Hypoperfusion]  --> [Recovery]   |
|   10 Hz Alpha            Diffuse Delta         Electrocerebral          Diffuse Delta|
|   Background             High-Voltage Slow     Suppression (<10 uV)     to Normal PDR|
|   |                      |                     |                        |            |
|   v                      v                     v                        v            |
|   (Baseline)       (Prodrome/Pallor)     (Myoclonic Jerks/Loss)   (Prompt Lucid)     |
+-------------------------------------------------------------------------------+

Clinical and Electrophysiological Profile:

• Prodrome: Lightheadedness, graying/tunneling of vision, diaphoresis, pallor, and nausea.
• Motor Semiology: Brief myoclonic twitches (arrhythmic, multifocal, lasting <10-15 seconds) or subtle tonic stiffening with upward eye gaze occurring after the patient collapses.
• The 'Slow-Flat-Slow' EEG Signature:
  1. Initial Slowing: As blood pressure and cerebral perfusion drop, the background degrades into diffuse, high-amplitude rhythmic delta activity.
  2. Generalized Suppression (Flatline): At peak hypoperfusion, the EEG flattens into severe generalized voltage suppression / electrocerebral silence (<10 µV). Myoclonic jerks characteristically occur during this flattening phase due to cortical disinhibition/brainstem reticular release.
  3. Return of Slowing: As perfusion resumes in the supine position, diffuse delta slowing reappears.
  4. Rapid Reconstitution: Prompt return to normal awake alpha background within 10-30 seconds, coinciding with immediate clinical reorientation without prolonged post-ictal confusion.
• Epileptiform Discharges: Completely absent throughout the recording.

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3. Parasomnias and Sleep-Related Events

REM Sleep Behavior Disorder (RBD)

• Pathophysiology: Loss of normal skeletal muscle atonia during REM sleep, allowing patients to physically act out vivid, often violent dreams (dream enactment behavior).
• Semiology: Punching, flailing, shouting, kicking, or falling out of bed during the second half of the night (when REM sleep predominates). Eyes remain closed.
• Key Differentiator: Upon awakening, the patient is immediately oriented, recalls the detailed dream, and shows normal REM sleep EEG on polysomnography with excessive chin/limb EMG tone (loss of atonia / RSWA) without cortical epileptiform discharges.

NREM Arousal Parasomnias

• Subtypes: Confusional arousals, sleep terrors, and sleepwalking (somnambulism).
• Features: Arise from slow-wave sleep (N3 / Stage 3-4 NREM) during the first third of the night; EEG displays diffuse delta slowing with sudden awakening artifact; patient exhibits autonomic agitation, amnesia for the event, and marked confusion without epileptiform spikes.

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4. The Critical Diagnostic Trap: Hypermotor Frontal Lobe Epilepsy vs. PNES

Sleep-Related Hypermotor Epilepsy (SHE) (formerly Nocturnal Frontal Lobe Epilepsy - NFLE) represents the most challenging differential diagnosis against PNES. Because SHE manifests with bizarre, dramatic motor behaviors (pelvic thrusting, bicycling, screaming, thrashing), many patients are mistakenly labeled with PNES for years.

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5. Movement Disorders & Physiologic Mimics

• Paroxysmal Kinesigenic Dyskinesia (PKD): Sudden dystonic posturing or choreoathetosis triggered by sudden voluntary movement (e.g., standing up quickly); lasts <1 minute; normal waking EEG throughout.
• Tics (Tourette Syndrome): Repetitive, semi-voluntary motor or vocal tics preceded by a premonitory urge; normal background.
• Hyperekplexia: Pathological exaggerated startle reflex in response to unexpected tactile/auditory stimuli, causing generalized stiffening and falls without loss of consciousness.