Epilepsy Mimics & DDx
Epilepsy Mimics & Differential Diagnosis
What You'll Learn
- 20–30% of "drug-resistant epilepsy" referrals do not have epilepsy — misdiagnosis is one of the most common errors in neurology
- PNES is the most important mimic: mean diagnostic delay 7–10 years; ictal eye closure (approximately 50–88% sensitivity, 74–96% specificity across studies; Chung 2006 et al.) is one of the more reliable semiologic distinguishing signs
- ECG is MANDATORY for every first seizure presentation — cardiac channelopathies (Long QT, CPVT, Brugada) cause convulsive syncope and carry risk of sudden death
- Convulsive syncope — convulsive movements occur in up to 90% of syncope episodes (Lempert 1994); myoclonic jerks during syncope are common, not rare, and do NOT indicate epilepsy
- Dual diagnosis: 10–50% of PNES patients also have true epilepsy — never assume all events are the same type
- Gold standard: video-EEG monitoring with capture of a habitual event. A habitual event with no ictal scalp EEG correlate strongly supports PNES when semiology is compatible, but consider scalp-negative frontal/deep seizures before calling an event non-epileptic.
HighYield Pearls
- PNES gold standard: video-EEG capturing the habitual spell with no ictal EEG correlate — treat with psychotherapy (CBT), NOT ASMs
- ECG on every first seizure: exclude Long QT, Brugada, CPVT, heart block — convulsive syncope from arrhythmia kills patients misdiagnosed as epilepsy
- Convulsive syncope is common: myoclonic jerks occur in up to 90% of syncopes — brief LOC <30 sec + prodrome + rapid recovery without postictal confusion = syncope, not seizure
- PKD (paroxysmal kinesigenic dyskinesia): brief <1 min movements triggered by sudden movement, preserved awareness, PRRT2 gene → dramatic response to carbamazepine (classic board point)
- PED + GLUT1 deficiency (SLC2A1): exercise-induced dyskinesia + low CSF glucose → ketogenic diet is both diagnostic and therapeutic
- RBD (REM sleep behavior disorder): dream enactment in older adults → prodromal α-synucleinopathy (PD, DLB, MSA); first-line treatment is melatonin
- TIA vs focal seizure: TIA = negative phenomena (weakness, numbness, loss of vision) in vascular distribution; seizure = positive phenomena (jerking, paresthesias, scintillations) with Jacksonian march
- Migraine aura march: slow 5–60 min spread of positive visual symptoms (fortification spectra, scintillating scotoma) — seizure aura is seconds, TIA is sudden-onset negative
- Cataplexy: sudden bilateral loss of muscle tone triggered by laughter/emotion with preserved consciousness — narcolepsy type 1 (low CSF hypocretin), NOT atonic seizure
- Pallid breath-holding spells in infants: vagally mediated after pain/startle → check hemoglobin/ferritin (iron deficiency association); treat with reassurance + iron if low
- Avoid the worst error: misdiagnosing PNES as refractory epilepsy → years of unnecessary ASMs, ICU admissions for "status," iatrogenic harm
🔍 Quick ReferenceDistinguishing features · Triggers / context · Workup / treatment
Distinguishing features
- Forced eye closure + pelvic thrusting + asynchronous flailing + side-to-side head shake + ictal crying + recall of event → PNES
- Brief LOC <30 sec + prodromal lightheadedness/nausea/visual greying + pallor + rapid recovery without postictal confusion → Syncope
- Convulsive jerks during cerebral hypoperfusion (myoclonic, brief, non-rhythmic) → Convulsive syncope (not epileptic)
- Dream enactment, punching/kicking bed partner in older adult → REM sleep behavior disorder (RBD)
- Screaming child sitting up in first third of night, inconsolable, no recall → NREM parasomnia (sleep terror)
- Brief <1 min abnormal movements + preserved awareness + dramatic carbamazepine response → PKD (PRRT2)
- Slow march of fortification spectra / scintillating scotoma over 5–60 min → Migraine aura
- Sudden focal NEGATIVE deficit in vascular territory, no positive features → TIA
- Sudden bilateral loss of tone with preserved consciousness → Cataplexy (narcolepsy type 1)
- Diaphoresis + tremor + confusion + fingerstick glucose <70, reverses with dextrose → Hypoglycemia
Triggers / context
- Emotional stress, history of trauma/abuse, comorbid PTSD or conversion disorder → PNES
- Prolonged standing, hot environment, venipuncture, micturition, defecation, emotional → Neurocardiogenic (vasovagal) syncope
- Syncope on EXERTION or SUPINE, family history of sudden cardiac death, young athlete → Cardiogenic syncope (Long QT, HCM, CPVT, Brugada)
- Standing up from supine, autonomic neuropathy, Parkinsonism, dehydration, antihypertensives → Orthostatic syncope
- Sudden voluntary movement (rising from chair, startle) → PKD
- Alcohol, caffeine, stress, fatigue (no movement trigger) → PNKD (PNKD/MR1)
- Prolonged exercise + low CSF glucose → PED (GLUT1 / SLC2A1 deficiency)
- Laughter, joking, surprise → brief loss of tone → Cataplexy
- Pain or startle → pale infant becomes limp/loses consciousness → Pallid breath-holding spell (iron deficiency association)
- Frustration/crying → cyanotic infant during expiratory apnea → Cyanotic breath-holding spell
- Positional head movement → sudden drop attack → Third ventricle colloid cyst
Workup / treatment
- Video-EEG with capture of habitual event + normal ictal EEG → PNES confirmed; treat with CBT (CODES trial), gradual ASM taper
- ECG + Holter + tilt-table + echo (long QT in young, structural heart disease) → Syncope workup
- Polysomnography (PSG) with video → Parasomnia workup; RBD = REM without atonia → melatonin first-line
- PRRT2 genetic testing + therapeutic trial of carbamazepine → PKD confirmation
- CSF glucose + SLC2A1 sequencing + ketogenic diet trial → GLUT1 deficiency / PED
- Orthostatic vitals (drop ≥20 systolic / ≥10 diastolic within 3 min standing) → Orthostatic syncope
- CSF hypocretin-1 low + MSLT with ≥2 SOREMPs → Narcolepsy/cataplexy
- ABCD2 score + urgent MRI/MRA + carotid imaging + cardiac monitor → TIA workup
- Fingerstick glucose + IV D50 → Hypoglycemia (reverses event)
- Hemoglobin, ferritin + reassurance + iron supplementation if deficient → Pallid breath-holding spell
- Multidisciplinary care (neurology + psychiatry) + empathetic delivery of diagnosis → PNES management (itself therapeutic)
PNES (Psychogenic Nonepileptic Seizures) — The Most Important Mimic
Epidemiology & Impact
- 20–30% of patients referred to epilepsy monitoring units with "drug-resistant epilepsy" have PNES
- Mean diagnostic delay: 7–10 years of unnecessary ASM exposure
- Also termed functional seizures or dissociative seizures (FND spectrum)
- Consequences: iatrogenic ASM toxicity, ICU admissions for "status," psychosocial burden
Semiologic Features
| Feature | Sensitivity | Specificity | Notes |
|---|---|---|---|
| Ictal eye closure | ~50–88% | ~74–96% | One of the more reliable semiologic signs (Chung 2006 et al.); eyes are typically open during epileptic GTCS |
| Waxing/waning course | 94% | Very high (>90%) | Fluctuating intensity with pauses; seizures evolve but do not wax/wane; caveat: frontal lobe seizures can mimic |
| Asynchronous limb movements | 84% | Very high (>90%) | Out-of-phase alternating; caveat: frontal lobe seizures can mimic |
| Duration >2 minutes | 65% | 93% | GTCS typically 1–2 min; PNES often 5–30 min |
| Side-to-side head movement | 63% | Very high (>90%) | Lateral head shaking during event; caveat: frontal lobe seizures can mimic |
| Pelvic thrusting | 24% | 97% | Low sensitivity but highly specific; rarely in frontal lobe epilepsy |
| Ictal crying/weeping | Low | Very high | Virtually pathognomonic when present |
Dual Diagnosis
- 10–50% of PNES patients also have coexisting epilepsy
- Each event type must be independently identified on video-EEG
- Never assume all events in one patient are the same type
Diagnosis
- Gold standard: video-EEG capturing habitual event with normal ictal EEG
- Staged approach (ILAE): documented → clinically established → confirmed (EEG-video confirmed)
- Prolactin: elevated after GTCS (not after PNES or absence)
- AAN guideline: serum prolactin >2× baseline, drawn 10–20 minutes post-event, supports GTCS or complex partial seizure (but does NOT exclude epilepsy if normal)
- Must draw within 10–20 minutes of the event
- Limited sensitivity; NOT reliable as sole diagnostic tool
- Often not elevated after frontal lobe seizures (variable across focal epilepsies)
Treatment
- Psychotherapy is the treatment — NOT ASMs
- CBT has the best evidence (CODES trial: CBT-informed therapy reduced seizure frequency)
- Empathetic communication of the diagnosis is itself therapeutic
- Gradual ASM taper if no concurrent epilepsy is safe and avoids iatrogenic harm; symptomatic improvement requires psychotherapy (CODES trial)
- Avoid iatrogenic harm: no IV benzodiazepines for prolonged PNES events
💎 Board Pearl
- Ictal eye closure throughout a convulsive event strongly suggests PNES. Eyes are typically open during epileptic GTCS; ictal eye closure throughout a convulsive event strongly suggests PNES. Reported sensitivity ~50–88% and specificity ~74–96% across studies (Chung 2006 et al.) — one of the more reliable semiologic signs, but not pathognomonic
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