THE EPIDEMIOLOGY OF EPILEPTIC ENCEPHALOPATHIES

Estimates of the incidence and prevalence of the various epileptic encephalopathies have been greatly hindered by the difficulties in reaching consensus on their diagnostic features. Delays in diagnosis have also hindered appropriate management.

Early recognition of suspicious clinical features may help the early recognition of these syndromes.

Syndrome (% childhood epilepsy)	Early Suspicious Features	Later Diagnostic Features
Dravet Syndrome (<0.5%)	– prolonged unilateral or bilateral febrile clonic seizures <1 year of age – normal EEG – normal development	– other seizure types: GTC, myoclonic, atypical absence, complex partial, repeated afebrile status epilepticus – psychomotor regression – diffuse slow waves + focal & generalized spike wave – ataxia + corticospinal signs
Lennox-Gastaut Syndrome (<5–10%)	– atonic seizures – tonic seizures in sleep	– other seizure types: tonic, atypical absence, myoclonic, GTC, partial – developmental regression – EEG- slow spike wave
Ohtahara Syndrome (<0.05%)	– tonic spasms in first 10 days of life – suppression-burst on wake & sleep EEG	– other seizure types: partial, GTC later in course – myoclonus RARE
West Syndrome (<2%)	– infantile spasms – hypsarrhythmia on EEG	– developmental regression
Early myoclonic epilepsy (<0.2%)	– erratic/fragmentary myoclonus early in life – suppression-burst on wake & sleep EEG	– other seizure types: partial, massive myoclonus, tonic
Doose Syndrome (myoclonic-astatic epilepsy) (<1%)	– prolonged recurrent GTC in 2–5 year olds – EEG – normal background – normal prior development	– other seizure types: myoclonic-astatic, atonic, atypical absence, recurrent status epilepticus – apraxia and dysarthria
Migrating partial epilepsy in infancy (<?)	– frequent focal seizures with apnea, cyanosis and flushing between 1 week and 7 months of age	– partial seizures vary from 1 seizure to the next – seizures almost continuous by end of 1st year
Rasmussen Syndrome (<?)	– GTC and/or partial – Todd's paresis	– focal neurological deficits – epilepsia partialis continua – progressive hemispheric atrophy – chronic encephalitis on biopsy
CSWS (<0.5%)	– cognitive deterioration – multiple partial and generalized seizures	– NO tonic seizures – EEG continuous S/W in slow sleep – – 1–2 years after first seizure – motor impairment
Landau-Kleffner Syndrome (<?)	– verbal auditory agnosia	– expressive aphasia – atypical absence, 20 GTC, eyelid myoclonus, atonic seizures – EEG: continuous S/W in slow sleep