Progressive Myoclonic & Reflex Epilepsies
Progressive Myoclonic Epilepsies & Reflex Epilepsies
What Do You Need to Know?
- PME triad: progressive ACTION myoclonus + epileptic seizures (GTC) + neurological decline (ataxia, cognitive deterioration)
- Key rule: if myoclonus is getting WORSE, the diagnosis is NOT JME — evaluate for PME
- Giant SEPs confirm cortical origin of myoclonus in all PME syndromes
- Phenytoin is STRICTLY contraindicated in all PME — causes irreversible cerebellar atrophy (especially ULD)
- Lafora disease: PAS-positive Lafora bodies on SKIN BIOPSY; occipital seizures; fatal within ~10 years
- CLN2 (NCL): cerliponase alfa = only FDA-approved disease-specific therapy for any PME
- Photosensitive epilepsy: PPR Grade 1 = normal variant (no treatment); Grade 3–4 = clinically significant
- Reading epilepsy: ILAE-recognized; jaw myoclonus while reading; stop reading = abort seizure
- Startle epilepsy: almost always structural brain disease; distinguish from hyperekplexia (GLRA1, not epileptic)
Progressive Myoclonic Epilepsies — Overview
The PME Triad
- Progressive action myoclonus: action-sensitive + stimulus-sensitive; worsens over months to years; cortical origin
- Epileptic seizures: GTC most common; myoclonic seizures; atypical absences in some
- Neurological decline: cerebellar ataxia (gait → limb → dysarthria) + cognitive deterioration (variable by etiology)
PME vs. JME — Critical Distinction
- PME: myoclonus progressively worsens; EEG background deteriorates; cognitive/motor decline over time
- JME: myoclonus is stable with treatment; EEG background remains normal; NO neurological decline
- Worsening myoclonus despite appropriate ASMs = red flag for PME
- Family history of consanguinity or affected siblings = suspect AR inheritance (most PMEs)
Neurophysiology
- Giant SEPs: dramatically enlarged cortical somatosensory evoked potentials; confirms cortical myoclonus
- EEG: generalized spike-wave / polyspike-wave; progressive background slowing; photoparoxysmal response
- Back-averaging: demonstrates cortical correlate time-locked to myoclonic jerks
💎 Board Pearl
- Phenytoin causes irreversible cerebellar atrophy in ULD — historically devastating before genetic diagnosis was possible
- ALL sodium channel blockers (CBZ, OXC, PHT) worsen myoclonus in PME — AVOID across all etiologies
- Vigabatrin also contraindicated — worsens myoclonus AND causes irreversible visual field loss (especially harmful in NCL)
Major PME Etiologies — Comparison
| Disease | Gene | Inheritance | Onset | Hallmark Feature | Prognosis |
|---|---|---|---|---|---|
| Unverricht-Lundborg (EPM1) | CSTB | AR | 6–15 y | Action myoclonus; cognition PRESERVED; no storage material | Best PME prognosis; survive decades |
| Lafora Disease (EPM2) | EPM2A / NHLRC1 | AR | 6–19 y | PAS+ Lafora bodies on SKIN BIOPSY; occipital seizures | Fatal ~10 years from onset |
| NCL (Batten disease) | CLN1–CLN14 | AR (most) | Infancy–adult | Visual loss + seizures + dementia; autofluorescent lipofuscin | Progressive; variable by type |
| Sialidosis Type I | NEU1 | AR | 8–25 y | Cherry-red spot + action myoclonus; cognition PRESERVED | Slow; near-normal lifespan |
| MERRF | MT-TK (m.8344A>G) | Maternal | Any age | Ragged-red fibers; lipomas; hearing loss; lactic acidosis | Variable; slowly progressive |
| DRPLA | ATN1 (CAG repeat) | AD | Variable | Chorea + dementia + ataxia; anticipation; Japanese | Progressive; reduced lifespan |
Individual PME Syndromes
Unverricht-Lundborg Disease (EPM1)
- Gene: dodecamer repeat expansion in CSTB promoter (chr 21q22.3); cysteine protease inhibitor
- Epidemiology: most common PME worldwide; endemic in Finland (Baltic myoclonus) and Mediterranean
- Onset: 6–15 years; myoclonus usually the presenting symptom
- Cognition: relatively preserved for decades — dramatically better than Lafora
- Treatment: VPA, clonazepam, LEV, perampanel; piracetam (8–24 g/day) antimyoclonic
- PHT causes irreversible cerebellar atrophy — STRICTLY avoid
Lafora Disease (EPM2)
- Genes: EPM2A (laforin, ~50%) or NHLRC1 (malin, ~40%)
- Pathology: Lafora bodies = PAS-positive, diastase-resistant polyglucosan inclusions
- Found in: neurons, myocytes, hepatocytes, eccrine sweat gland duct cells (basis for SKIN BIOPSY)
- Hallmark: occipital seizures with visual hallucinations early in course
- Course: rapid cognitive decline → dementia → status epilepticus → death ~10 years
- Diagnosis: axillary skin biopsy (~80% sensitivity); genetic testing first-line
- Emerging: antisense oligonucleotides targeting glycogen synthase; metformin (preclinical)
Sialidosis Type I (Cherry-Red Spot Myoclonus)
- Gene: NEU1 (neuraminidase 1); AR
- Key features: bilateral cherry-red spot (~95%) + severe action myoclonus + ataxia
- Cognition: generally PRESERVED (distinguishes type I from type II)
- No hepatosplenomegaly or dysmorphic features (type I)
- Diagnosis: elevated urine sialyloligosaccharides; deficient neuraminidase enzyme activity
MERRF
- Mutation: m.8344A>G in MT-TK (tRNALys); maternal inheritance
- Core features: myoclonus + GTC + ataxia + myopathy
- Red flags: hearing loss + lipomas + short stature + elevated lactate
- Muscle biopsy: ragged-red fibers (Gomori trichrome); COX-negative fibers
- VPA with CAUTION: hepatotoxicity risk in mitochondrial disease (especially POLG); LEV, clonazepam safer
DRPLA
- Gene: ATN1 — CAG trinucleotide repeat expansion; autosomal dominant
- Anticipation: longer repeats → earlier onset, more severe phenotype in successive generations
- Juvenile onset: PME phenotype (myoclonus, seizures, ataxia)
- Adult onset: chorea, dementia, ataxia, psychiatric features
- Epidemiology: predominantly Japanese; rare outside East Asia
Neuronal Ceroid Lipofuscinoses (NCL) — Key Types
| CLN Type | Gene | Onset | Key Feature | EM Finding |
|---|---|---|---|---|
| CLN1 (infantile) | PPT1 | 6 mo–2 y | Rapid motor/cognitive decline; microcephaly | Granular osmiophilic deposits (GROD) |
| CLN2 (late infantile) | TPP1 | 2–4 y | Seizures (initial); cerliponase alfa FDA-approved | Curvilinear profiles |
| CLN3 (juvenile) | CLN3 | 4–10 y | Visual loss (initial symptom); cognitive decline | Fingerprint profiles |
| CLN5 (Finnish variant) | CLN5 | 4–7 y | Motor clumsiness; visual loss; myoclonus | Mixed patterns |
| CLN6 (variant late infantile/adult) | CLN6 | 18 mo–adult | Seizures; Kufs type A (adult form) | Mixed patterns |
| CLN8 (Northern epilepsy) | CLN8 | 5–10 y | GTC seizures; slow cognitive decline; Finnish | Curvilinear / GROD |
- CLN2 = cerliponase alfa (intracerebroventricular enzyme replacement) — only FDA-approved NCL therapy (2017)
- Diagnosis: PPT1/TPP1 enzyme assays in leukocytes (CLN1/CLN2); EM of skin biopsy; genetic testing
- All NCL: progressive visual loss + seizures + cognitive/motor decline = suspect NCL
Diagnostic Approach to PME
Step-by-Step Algorithm
- Step 1 — Clinical recognition: progressive myoclonus + seizures + decline → differentiate from JME
- Step 2 — Neurophysiology: EEG (background slowing, polyspike-wave); giant SEPs; back-averaging
- Step 3 — Ophthalmology: cherry-red spot (sialidosis); retinal degeneration (NCL); optic atrophy (MERRF)
- Step 4 — Skin biopsy: Lafora bodies (PAS+, eccrine ducts); curvilinear/fingerprint profiles (NCL by EM)
- Step 5 — Enzyme assays: PPT1/TPP1 (NCL); neuraminidase (sialidosis); glucocerebrosidase (Gaucher)
- Step 6 — Genetic testing: exome sequencing (first-line per ILAE); mitochondrial DNA; targeted panels
- Step 7 — Muscle biopsy: ragged-red fibers + COX staining (MERRF) when genetics inconclusive
Treatment Principles for All PME
Useful ASMs
- Valproate (first-line; CAUTION in mitochondrial disease)
- Levetiracetam / brivaracetam
- Clonazepam (often most effective single agent for cortical myoclonus)
- Perampanel (emerging evidence, especially ULD)
- Piracetam (high dose 8–24 g/day; antimyoclonic)
AVOID in All PME
- Phenytoin — irreversible cerebellar atrophy
- Carbamazepine / oxcarbazepine — worsen myoclonus
- Vigabatrin — worsens myoclonus + irreversible VF loss
- Gabapentin / pregabalin — may worsen myoclonus
- Lamotrigine — may worsen myoclonus (occasionally useful for GTC only)
Reflex Epilepsies — Overview
Definition & Key Concepts
- Reflex seizures: consistently triggered by specific sensory stimuli or cognitive activities
- NOT the same as reactive triggers (sleep deprivation, alcohol) that lower threshold nonspecifically
- May occur within IGE (JME + photosensitivity), focal epilepsy (musicogenic TLE), or as sole seizure type
- ILAE 2022 recognizes: reading epilepsy and photosensitive occipital lobe epilepsy as defined syndromes
Photosensitive Epilepsy
Epidemiology
- Prevalence: PPR in 2–5% of all epilepsy patients
- Peak: adolescence (10–18 years); declines after 3rd decade; rare after age 50
- Sex: female predominance (~60–70%)
- Most epileptogenic frequency: 15–25 Hz flash rate
PPR Grading (Waltz Classification)
| PPR Grade | EEG Description | Clinical Significance |
|---|---|---|
| Grade 1 | Occipital spikes time-locked to flashes | Normal variant — NO treatment needed |
| Grade 2 | Parieto-occipital spikes + biphasic slow waves | Borderline; context-dependent |
| Grade 3 | Parieto-occipital spikes + generalized SW/PSW | Clinically significant |
| Grade 4 | Generalized SW/PSW ± occipital component | Most significant; strongest seizure correlation |
Syndrome Associations
- Epilepsy with eyelid myoclonia (EEM): PPR ~100% — defining feature
- JME: PPR 30–90% — most commonly tested association
- CAE: PPR 5–15%
- Dravet syndrome: PPR 30–50%
Management
- Z1 blue-tinted lenses: reduce PPR by up to 75%; efficacy confirmable on EEG
- Monocular occlusion: covering one eye interrupts binocular stimulation — emergency abort strategy
- Screen distance: ≥2 meters; reduced brightness; ambient room lighting; ≥100 Hz refresh rate
- Pharmacotherapy: VPA most effective for photosensitive IGE; LEV reduces PPR; CLB as adjunct
- Natural history: PPR often decreases after 3rd decade, particularly in women
Pokemon Incident (1997)
- Pokemon episode broadcast rapidly alternating red-blue flashes at ~12 Hz
- 685 Japanese children experienced seizures; 150 hospitalized
- Led to Japan, UK (Ofcom), ITU broadcasting guidelines; W3C WCAG: ≤3 flashes/second
Reading Epilepsy
Clinical Features
- ILAE-recognized syndrome (combined generalized + focal epilepsy with variable age onset)
- Onset: late adolescence / young adulthood (12–25 years)
- Hallmark: jaw myoclonus (rhythmic jaw clicking/jerking) triggered by reading
- If reading continues → may generalize to GTC
- Stop reading = abort seizure — most important management step
- Reading aloud more provocative than silent reading
- EEG: interictal normal; ictal = bilateral SW/PSW, left hemisphere predominance
- Origin: usually temporal lobe (language network); MRI normal
- Treatment: reading breaks; VPA (most effective); LEV, CLB, clonazepam
Startle Epilepsy
Clinical Features
- Almost always structural brain disease (perinatal injury, cortical dysplasia, cerebral palsy)
- Seizure type: brief tonic seizures (<30 sec); may cause falls
- Trigger: unexpected auditory or somatosensory stimuli (unexpectedness is key, not intensity)
- Most patients: intellectual disability + spastic hemiparesis/quadriparesis
Startle Epilepsy vs. Hyperekplexia
| Feature | Startle Epilepsy | Hyperekplexia |
|---|---|---|
| Mechanism | Epileptic (cortical) | NOT epileptic (brainstem) |
| Genetics | Usually structural etiology | GLRA1 mutations (glycine receptor) |
| Onset | Childhood (with brain lesion) | Neonatal |
| EEG | Epileptiform discharge | NO epileptiform correlate |
| Semiology | Tonic seizures | Exaggerated startle + stiffness |
| Treatment | ASMs (CLB, clonazepam, VPA) | Clonazepam (highly responsive) |
- Drug resistance common in startle epilepsy due to structural pathology
- Callosotomy for refractory drop attacks from tonic seizures
Other Reflex Epilepsies
Hot Water Epilepsy
- Geography: predominantly South India, Turkey
- Trigger: hot water (≥40–45°C) poured over head/body; temperature-specific
- Seizure type: focal impaired awareness (70%); may generalize
- Critical fact: 30–50% develop spontaneous seizures over time
- Treatment: lukewarm bathing; intermittent CLB pre-bath; VPA for frequent seizures
Musicogenic Epilepsy
- Rare: ~1 in 10,000,000 general population
- Trigger: specific musical stimuli (instrument, genre, emotional quality)
- Origin: focal temporal lobe; right hemisphere predominance
- Treatment: CBZ, LTG, LEV; trigger avoidance; surgery in refractory cases
Other Types
- Eating epilepsy: triggered by chewing/swallowing; temporal/frontal origin
- Thinking / praxis-induced: calculation, decision-making; associated with JME; generalized
- Pattern-sensitive: high-contrast geometric patterns; coexists with photosensitivity
- Eye closure sensitivity: defines EEM (Jeavons syndrome)
Board Pearls & Clinical Pearls
💎 Board Pearl
- If myoclonus is worsening, the diagnosis is NOT JME — the single most important rule for PME recognition
- Lafora disease = skin biopsy: PAS-positive Lafora bodies in eccrine sweat gland duct cells (~80% sensitivity); the only PME routinely diagnosed by skin biopsy
- Cherry-red spot + myoclonus + preserved cognition = sialidosis type I — distinguish from Tay-Sachs (infantile, no myoclonus)
- MERRF clue: myoclonus + lipomas + hearing loss + maternal inheritance → check m.8344A>G
- PPR Grade 1 = normal variant — do NOT treat; only Grade 3–4 are clinically significant
- Reading epilepsy: jaw myoclonus is pathognomonic; stop reading = abort seizure and prevent GTC
- Hyperekplexia vs. startle epilepsy: hyperekplexia = NOT epileptic (GLRA1, brainstem); startle epilepsy = epileptic (structural, cortical); EEG differentiates
Clinical Pearl
VPA in mitochondrial disease: Valproate carries risk of fatal hepatotoxicity, particularly in POLG-related disease. In MERRF (MT-TK), risk is less established but caution warranted. Always check POLG status before starting VPA in suspected mitochondrial epilepsy. LEV and clonazepam are safer alternatives.
Clinical Pearl
Z1 blue-tinted lenses reduce the photoparoxysmal response by up to 75% and can be tested during EEG to confirm individual efficacy. Combined with monocular occlusion as an emergency abort strategy, these are highly board-relevant non-pharmacologic interventions for photosensitive epilepsy.
Clinical Pearl
Hot water epilepsy: geographically restricted (South India, Turkey) but board-relevant because 30–50% of patients eventually develop spontaneous seizures, transforming a pure reflex epilepsy into chronic epilepsy requiring long-term ASM therapy.
References
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