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content:dravet_syndrome [2020/02/18 07:00] – [Seizure semiology] bijuhameedcontent:dravet_syndrome [2020/02/23 19:55] – [Epilepsy surgery] icna
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   * Incidence probably less than 1 per 40,000   * Incidence probably less than 1 per 40,000
   * Males are more often affected than females, in a ratio of 2:1.   * Males are more often affected than females, in a ratio of 2:1.
-===== History & Clinical Manifestations =====+===== Clinical features =====
   * Dravet syndrome typically occurs in normal infants   * Dravet syndrome typically occurs in normal infants
   * Significant antenatal associations reported in literature include intrauterine growth retardation, prematurity and hypoxic ischemic insults   * Significant antenatal associations reported in literature include intrauterine growth retardation, prematurity and hypoxic ischemic insults
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   * Behaviour becomes more characterised by slowness and perseveration.   * Behaviour becomes more characterised by slowness and perseveration.
 ===== Seizure semiology ===== ===== Seizure semiology =====
-  * the Seizures typically begin before 1 year of age +  * seizures typically begin before 1 year of age 
-  * initially they are prolonged, generalized, or unilateral clonic seizures and are typically triggered by fever+  * __initially they are prolonged, generalized, or unilateral clonic seizures and are typically triggered by fever__
   * the febrile seizures tend to be long (more than 20 min), recur in clusters in the same day and evolve into status epilepticus   * the febrile seizures tend to be long (more than 20 min), recur in clusters in the same day and evolve into status epilepticus
   * sometimes afebrile seizures can also occur initially usually in the context of a vaccination or of an infectious episode, or after a bath but majority of these patients then go on to have febrile seizures   * sometimes afebrile seizures can also occur initially usually in the context of a vaccination or of an infectious episode, or after a bath but majority of these patients then go on to have febrile seizures
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   * About 2 weeks to 2 months ( mean 6 weeks) following the first febrile seizure other febrile seizures occur and later afebrile seizures also appear (mean 5 months).   * About 2 weeks to 2 months ( mean 6 weeks) following the first febrile seizure other febrile seizures occur and later afebrile seizures also appear (mean 5 months).
   * Between 1 and 4 years of age, other seizure types appear, along with a slowing in the psychomotor development attaining a steady state in the disease progress.   * Between 1 and 4 years of age, other seizure types appear, along with a slowing in the psychomotor development attaining a steady state in the disease progress.
-  * once a steady state is achieved then multiple seizure types during the course of the disease +  * __once a steady state is achieved then multiple seizure types during the course of the disease__ 
- +  * **Generalized clonic or tonic clonic seizures**
-**Convulsive Seizures** +
-  * Generalized clonic or tonic clonic seizures+
     * usually shorter, with a very brief tonic phase, with few autonomic symptoms, with a transient postictal flattening quickly replaced by diffuse delta waves     * usually shorter, with a very brief tonic phase, with few autonomic symptoms, with a transient postictal flattening quickly replaced by diffuse delta waves
     * in some seizures, the initial tonic phase is almost immediately mixed with the clonic jerks, giving a vibratory aspect     * in some seizures, the initial tonic phase is almost immediately mixed with the clonic jerks, giving a vibratory aspect
-  * Unilateral seizures+  * **Unilateral seizures**
     * short duration, associated with contralateral tone changes     * short duration, associated with contralateral tone changes
     * ictal EEG anomalies more limited to one hemisphere. They can begin with diffuse spike-waves     * ictal EEG anomalies more limited to one hemisphere. They can begin with diffuse spike-waves
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     * However, the EEG discharge involves irregularly different parts of the brain. It can start in one localized area of one hemisphere, then spread either to the entire hemisphere, either asymmetrically to the two hemispheres, or to another area of the same hemisphere or of the opposite hemisphere, then return to the first involved hemisphere. The end of the discharge can occur either in this hemisphere or contralaterally     * However, the EEG discharge involves irregularly different parts of the brain. It can start in one localized area of one hemisphere, then spread either to the entire hemisphere, either asymmetrically to the two hemispheres, or to another area of the same hemisphere or of the opposite hemisphere, then return to the first involved hemisphere. The end of the discharge can occur either in this hemisphere or contralaterally
     * The ways of propagation are very variable from one seizure to another in the same patient and even in the same recording. The relationship between the clinical events and the accompanying EEG is not always clear.     * The ways of propagation are very variable from one seizure to another in the same patient and even in the same recording. The relationship between the clinical events and the accompanying EEG is not always clear.
-  * Myoclonic Seizures +  * **Myoclonic Seizures** 
-    * The myoclonic seizures appear between the ages of 1 and 5 years +    * myoclonic seizures appear between the ages of 1 and 5 years 
-    * They are difficult to analyze due to their variability. Sometimes they are barely evident while at times they are massive involving whole muscles. +    * they can be quite variable & sometimes there is an atonic component associated with a head drop 
-    * Sometimes there is an atonic component associated with a head drop. +    * sometimes they are isolated or grouped in brief bursts consisting of two or three jerks 
-    * The myoclonic jerks can be either isolated or grouped in brief bursts, consisting of two or three jerks. +    * they are very frequent, occurring several times a day, sometimes incessantly.
-    * They are very frequent, occurring several times a day, sometimes incessantly.+
     * Interictal segmental myoclonus are often seen sometimes appearing only before a convulsive seizure with no concomitant change in the EEG. They involve either the limbs of the both sides, with a distal predominance, or the facial muscles, independently.     * Interictal segmental myoclonus are often seen sometimes appearing only before a convulsive seizure with no concomitant change in the EEG. They involve either the limbs of the both sides, with a distal predominance, or the facial muscles, independently.
     * They exist at rest, but are increased by voluntary movement.     * They exist at rest, but are increased by voluntary movement.
     * They are more frequent in the period with seizures, particularly in elder children with frequent nocturnal convulsive seizures, after awakening from attacks.     * They are more frequent in the period with seizures, particularly in elder children with frequent nocturnal convulsive seizures, after awakening from attacks.
-    * In hyperactive children the myoclonus could be made evident by asking them to perform a precise activity such as drinking, piling up cubes, or holding a spoon. +    * in hyperactive children the myoclonus could be made evident by asking them to perform a precise activity such as drinking, piling up cubes, or holding a spoon. 
-    * The myoclonic jerks are sometimes observed only on awakening or in the minutes preceding a seizure. +    * the myoclonic jerks are sometimes observed only on awakening or in the minutes preceding a seizure. 
-    * They persist during drowsiness and disappear during slow sleep. +    * they persist during drowsiness and disappear during slow sleep. 
-    * The jerks can be initiated by photic stimulation, variation in light intensity, closure of the eyes, and fixation on patterns. +    * the jerks can be initiated by photic stimulation, variation in light intensity, closure of the eyes, and fixation on patterns. 
-    * They are not typically accompanied by changes in consciousness, except when they occur at very close intervals. +    * they are not typically accompanied by changes in consciousness, except when they occur at very close intervals. 
-    * Video EEG has shown that they are accompanied by generalized or multiple spike-waves, at 3 Hz or more, with higher voltage on the frontocentral areas and on the vertex. Their duration is usually brief (1–3 s), but it can be longer (10 s).  +    * telemetry studies indicate that they are accompanied by generalized or multiple spike-waves, at 3 Hz or more, with higher voltage on the frontocentral areas and on the vertex. Their duration is usually brief (1–3 s), but it can be longer (10 s).  
-    * Electromyography (EMG) can show the postmyoclonic inhibition corresponding to the head drop. +    * electromyography (EMG) can show the postmyoclonic inhibition corresponding to the head drop. 
-    * Sometimes there is successive myoclonic twitching involving mostly head, eyelids, and, at times, arms, resulting in a rhythmic retropulsion of head corresponding to a burst of generalized spike-waves at 3 Hz. When they are sufficiently sustained, they appear to be atypical absence seizures with a myoclonic component. +    * sometimes there is successive myoclonic twitching involving mostly head, eyelids, and, at times, arms, resulting in a rhythmic retropulsion of head corresponding to a burst of generalized spike-waves at 3 Hz. When they are sufficiently sustained, they appear to be atypical absence seizures with a myoclonic component. 
-  * **Atypical Absence Seizures**+  * **Atypical absence seizures**
     * Atypical absence seizures can appear at different ages, either between 1 and 3 years, together with the myoclonic attacks, or later on, from 5 to 12 years.     * Atypical absence seizures can appear at different ages, either between 1 and 3 years, together with the myoclonic attacks, or later on, from 5 to 12 years.
-    * They can be either atypical absence seizures with impaired consciousness only or with a myoclonic component as well. +    * they can be either atypical absence seizures with impaired consciousness only or with a myoclonic component as well. 
-    * Both seizure types correspond to generalized, irregular spike-waves at 2–3.5 Hz +    * both seizure types correspond to generalized, irregular spike-waves at 2–3.5 Hz 
-  * **Obtundation Status** +  * **Obtundation status** 
-    * Characterised by a variable impairment of consciousness often accompanied by fragmentary and segmental, erratic myoclonias, of low amplitude, involving the limbs and the face, sometimes associated with a slight increase of muscular tone. +    * characterised by a variable impairment of consciousness often accompanied by fragmentary and segmental, erratic myoclonias, of low amplitude, involving the limbs and the face, sometimes associated with a slight increase of muscular tone. 
-    * Depending on the level of consciousness patients can or cannot react to stimuli, have simple activities (toy manipulation and eating), interrupted by short episodes of complete loss of contact and staring. Strong sensory stimulations can interrupt but not stop the status. +    * depending on the level of consciousness patients can or cannot react to stimuli, have simple activities (toy manipulation and eating), interrupted by short episodes of complete loss of contact and staring. Strong sensory stimulations can interrupt but not stop the status. 
-    * Convulsive seizures could either initiate, occur during, or terminate these status. These periods could be prolonged for several hours, even several days, maintained by environmental light stimuli, eye closure, and the pattern fixation (dotted lines of the walls, TV screen in two recorded status). +    * convulsive seizures could either initiate, occur during, or terminate these status. These periods could be prolonged for several hours, even several days, maintained by environmental light stimuli, eye closure, and the pattern fixation (dotted lines of the walls, TV screen in two recorded status). 
-    * The EEG is characterized by one diffuse slow-wave dysrrhyhmia, intermixed with rare focal and diffuse spikes, sharp waves, and spike-waves, of higher voltage in the anterior regions and the vertex, without correspondence between the spikes and the myoclonias, except during the myoclonic fits.+    * EEG is characterized by one diffuse slow-wave dysrrhyhmia, intermixed with rare focal and diffuse spikes, sharp waves, and spike-waves, of higher voltage in the anterior regions and the vertex, without correspondence between the spikes and the myoclonias, except during the myoclonic fits.
     * EEG corresponding to a complex partial status with either continuous posterior localized irregular slow waves or spike-waves during unconsciousness with deviations of both eyes to the right or irregular spike-wave complexes over the left hemisphere, predominantly in the occipitotemporal area have also been reported.     * EEG corresponding to a complex partial status with either continuous posterior localized irregular slow waves or spike-waves during unconsciousness with deviations of both eyes to the right or irregular spike-wave complexes over the left hemisphere, predominantly in the occipitotemporal area have also been reported.
-  * **Focal Seizures** +  * **Focal seizures** 
-    * Focal seizures can appear early, from 4 months to 4 years . They are either Simple partial seizures (SPS) of motor type or more commonly complex partial seizures (CPS), with prominent autonomic symptoms. When the symptomatology is mild, it is difficult to distinguish them from atypical absences without concomitant EEG. The partial seizures could be secondarily generalized.+      * Focal seizures can appear early, from 4 months to 4 years. 
 +      * they are either Simple partial seizures (SPS) of motor type or more commonly complex partial seizures (CPS), with prominent autonomic symptoms. When the symptomatology is mild, it is difficult to distinguish them from atypical absences without concomitant EEG. The partial seizures could be secondarily generalized. 
 +  * **Tonic seizures** 
 +    * tonic seizures are exceptional in Dravet syndrome and are mainly detected by sleep EEG recordings. When present they resemble the axial tonic seizures of the [[Lennox–Gastaut syndrome]] (LGS), sometimes with a myoclonic component but unlike LGS not frequently repeated in the same recording nor the interictal sleep EEG commonly shows rapid rhythms and multiple SWs like in LGS.
  
-**Tonic Seizures** +===== Neurophysiology ===== 
-Tonic seizures are exceptional in Dravet syndrome and are mainly detected by sleep EEG recordings. When present they resemble the axial tonic seizures of the Lennox–Gastaut syndrome (LGS), sometimes with a myoclonic component but unlike LGS not frequently repeated in the same recording nor the interictal sleep EEG commonly shows rapid rhythms and multiple SWs like in LGS. +  * EEGs are usually normal at disease onset. The background activity is slow when there has been numerous convulsive seizures. Otherwise it can be either normal or slow and disorganized. 
- +  * Rhythmic theta activities at 4–5 Hz can also be present in the centroparietal areas and the vertex 
-**Interictal EEG** +  * the interictal EEG often changes with the progression of the condition with the occurrence of generalized, focal, and multifocal abnormalities. 
-The EEGs often change with the progression of the condition with the occurrence of generalized, focal, and multifocal abnormalities. Characteristically specific features are absent. The background activity is slow when the convulsive seizures are numerous. Out of these periods it can be either normal or slow and disorganized. +  * paroxysmal abnormalities are also variable and can be absent. When present, they consist of spikes, single and multiple spike-waves, generalized, symmetric or asymmetric, isolated or in brief bursts, and of localized sharp waves, slow waves, and spikes. 
- +  * localized findings are usually seated in the central areas, bilaterally, synchronous or asynchronous, and in the vertex, and may spread to the entire hemisphere but can be also recorded in the posterior regions, occipital or temporal. 
-Sometimes a rhythmical theta activity is recorded in the central and vertex areas. +  * The EEGs contain more generalized paroxysms when myoclonic jerks are present. The relationship between the seat of the interictal paroxysms and the ictal discharges are not always clear. 
- +  * **Hyperventilation:** variable response 
-The paroxysmal abnormalities are also variable and can be absent. When present, they consist of spikes, single and multiple spike-waves, generalized, symmetric or asymmetric, isolated or in brief bursts, and of localized sharp waves, slow waves, and spikes. The localized findings are usually seated in the central areas, bilaterally, synchronous or asynchronous, and in the vertex, and may spread to the entire hemisphere but can be also recorded in the posterior regions, occipital or temporal. The EEGs contain more generalized paroxysms when myoclonic jerks are present. The relationship between the seat of the interictal paroxysms and the ictal discharges are not always clear. +  * **Eye closure:** The eye closure may facilitate the occurrence of localized and generalized abnormalities. 
- +  * **Sleep:** Sleep is usually well structured with physiological patterns and cyclic organization, except when several seizures occur during the night. The paroxysmal, generalized as well as localized, activities are enhanced or appear. 
-Hyperventilation: The response to hyperventilation is variable. +  * **Photosensitivity:** Photosensitivity on EEG is variable. Seizures have been reported to become very frequent under bright conditions, while they were remarkably reduced in the dark. Early photosensitivity is noted with generalized spike-waves following intermittent photic stimulation (IPS). There is a discrepancy between photosensitivity in the EEG lab and day to day life clinical photosensitivity.Patients with SME seem to have a paroxysmal response different from that observed in patients with idiopathic generalized epilepsy, dependent on the quantity of light rather than wavelength[(:cite:10496248>{{pubmed>10496248}})]. The constant light sensitivity might correspond to the strongest end of the photosensitive spectrum in SME patients representing the most resistant type in SME. 
- +  * **Fever Sensitivity:**  
-Eye closure: The eye closure may facilitate the occurrence of localized and generalized abnormalities. +    * Epileptic seizures in SME are very sensitive to body temperature elevation itself, regardless of etiology, either due to infection, hot baths, or even physical exercise. In the Japanese population, frequent seizures triggered by fever and Japanese style hot-water immersion have been reported. The convulsive seizures are often prolonged and develop into status during such episodes. 
- +    * Even though the fever sensitivity is most prominent during infancy and the hyperthermia and infections continue to remain as potential triggers and febrile status epilepticus can still occur during adolescence. 
-Sleep: Sleep is usually well structured with physiological patterns and cyclic organization, except when several seizures occur during the night. The paroxysmal, generalized as well as localized, activities are enhanced or appear. +  * **Segmentary interictal myoclonus:** In segmentary interictal myoclonus, time-locked EEG potentials are not detectable and [[C-reflex]] and enlarged [[somatosensory evoked potentials]] are absent. These small jerks either are not produced in the cortex or result from discharges involving such a small number of neurons that their electrical activity is undetectable. 
- +  * **Generalized ictal myoclonic jerks:** The generalized ictal myoclonic jerks are always preceded by clear-cut spike-wave discharges. They are thought to originate from the spread of focal cortical myoclonic activity. However, the leading hemisphere shifts from one discharge to the next, according to the muscle used as trigger, with an interside latency consistent with transcallosal spread. Thus, there is some evidence that myoclonus in SME can originate, like the other seizures, from multiple cortical areas.
-Photosensitivity +
- +
-EEG photosensitivity has been observed variably in patients. Sseizures have been reported to become very frequent under bright conditions, while they were remarkably reduced in the dark. A strong response to IPS was also observed. There is a discrepancy between photosensitivity in the EEG lab and day to day life clinical photosensitivity. +
- +
-Patients with SME seem to have a paroxysmal response different from that observed in patients with idiopathic generalized epilepsy, dependent on the quantity of light rather than wavelength. The constant light sensitivity might correspond to the strongest end of the photosensitive spectrum in SME patients representing the most resistant type in SME +
- +
-Fever Sensitivity +
- +
-Epileptic seizures in SME are very sensitive to body temperature elevation itself, regardless of etiology, either due to infection, hot baths, or even physical exercise. In the Japanese population, frequent seizures triggered by fever and Japanese style hot-water immersion have been reported. The convulsive seizures are often prolonged and develop into status during such episodes. There is no evidence however to link SME with increased susceptibility to infections. +
- +
-Even though the fever sensitivity is most prominent during infancy and the hyperthermia and infections continue to remain as potential triggers and febrile status epilepticus can still occur during adolescence. +
- +
-===== Neurophysiology =====EEGs are usually normal at disease onset. Sometimes a diffuse or unilateral slowing of the background if they are recorded after a prolonged seizure. Early photosensitivity is noted with generalized spike-waves elicited by the intermittent photic stimulation (IPS). Rhythmic theta activities at 4–5 Hz can also be present in the centroparietal areas and the vertex +
- +
-Segmentary interictal myoclonus: In segmentary interictal myoclonus, time-locked EEG potentials are not detectable and C-reflex and enlarged somatosensory evoked potentials are absent. These small jerks either are not produced in the cortex or result from discharges involving such a small number of neurons that their electrical activity is undetectable. +
- +
-**Generalized ictal myoclonic jerks:** The generalized ictal myoclonic jerks are always preceded by clear-cut spike-wave discharges. Available evidence suggests that they originate from the spread of focal cortical myoclonic activity. However, the leading hemisphere shifts from one discharge to the next, according to the muscle used as trigger, with an interside latency consistent with transcallosal spread. Thus, there is some evidence that myoclonus in SME can originate, like the other seizures, from multiple cortical areas.+
  
 ===== Neuroimaging ===== ===== Neuroimaging =====
-Neuroimaging do not normally show any abnormalities particularly malformations. However, CT scan and MRI can show signs of slight or moderate, diffuse, cerebral atrophy, cerebellar atrophy, sometimes increased white matter signal (T2 weight). In some cases, neuroimaging may be normal at the onset with the cerebral atrophy appearing during the course of epilepsy. +  * Neuroimaging do not normally show any abnormalities particularly malformations. 
- +  * somtimes signs of slight or moderate, diffuse, cerebral atrophy, cerebellar atrophy or increased white matter signal (T2 weight) can be seen 
-Interictal SPECT could be normal or show areas of hypoperfusion localised in one or both hemispheres. The areas of hypoperfusion not necessarily in concordance with the prevalence of EEG paroxysms. PET studies have also been either normal or showing hypometabolism with no consistent correlation between the focal ictal symptoms.+  * in some cases, neuroimaging may be normal at the onset with the cerebral atrophy appearing during the course of epilepsy. 
 +  * interictal SPECT could be normal or show areas of hypoperfusion localised in one or both hemispheres. The areas of hypoperfusion not necessarily in concordance with the prevalence of EEG paroxysms 
 +  * PET studies have also been either normal or showing hypometabolism with no consistent correlation between the focal ictal symptoms.
  
 ===== Genetics ===== ===== Genetics =====
-  * Between 70% and 80% of patients carry sodium channel α1 subunit gene (SCN1A) abnormalities+  * Between 70% and 80% of patients carry sodium channel α1 subunit gene ([[https://www.omim.org/entry/182389|SCN1A]]) abnormalities
   * truncating mutations account for about 40% and have a significant correlation with an earlier age of seizures onset[(:cite:21463275>{{pubmed>21463275}})].   * truncating mutations account for about 40% and have a significant correlation with an earlier age of seizures onset[(:cite:21463275>{{pubmed>21463275}})].
- +  * remaining SCN1A mutations comprise [[splice_site_mutation|splice-site]] and [[https://www.genome.gov/genetics-glossary/Missense-Mutation|missense mutations]], most of which fall into the pore-forming region of the sodium channel 
-The remaining SCN1A mutations comprise splice-site and missense mutations, most of which fall into the pore-forming region of the sodium channel. Mutations are randomly distributed across the SCN1A protein. Most mutations are de novo, but familial SCN1A mutations also occur. +  * mutations are randomly distributed across the SCN1A protein 
- +  * most mutations are de novo, but familial SCN1A mutations also occur. 
-Somatic mosaic mutations have also been reported in some patients and might explain the phenotypical variability seen in some familial cases. SCN1A exons deletions or chromosomal rearrangements involving SCN1A and contiguous genes are also detectable in about 2–3% of patients. A small percentage of female patients with a DS-like phenotype might carry PCDH19 mutations. Rare mutations have been identified in the GABARG2 and SCN1B genes. The etiology of about 20% of DS patients remains unknown, and additional genes are likely to be implicated. +  * [[Somatic mosaic mutations]] have also been reported in some patients and might explain the phenotypical variability seen in some familial cases. 
- +  * SCN1A exons deletions or chromosomal rearrangements involving SCN1A and contiguous genes are also detectable in about 2–3% of patients. 
-A majority of cases have a family history of epilepsy or febrile seizures (FS).+  * A small percentage of female patients with a DS-like phenotype might carry [[https://www.omim.org/entry/300460|PCDH19]] mutations. 
 +  * Rare mutations have been identified in the [[GABARG2]] and [[https://www.omim.org/entry/600235|SCN1B]] genes. 
 +  * The etiology of about 20% of DS patients remains unknown, and additional genes are likely to be implicated. 
 +  * A majority of cases have a family history of epilepsy or febrile seizures (FS). 
 +===== Pathophysiology ===== 
 +  * The voltage-gated sodium channel is responsible for the initiation of action potentials and, therefore, is involved in neuronal excitability[(:cite:16921370>)][(:cite:18804930>{{pubmed>18804930}})]. 
 +  * The α subunit has 4 homologous domains, with 6 transmembrane segments each, that form the voltage sensor and ion-conducting pore[(:cite:16921370>)]. 
 +  * Mutations cause either a gain or a loss of function[(:cite:18804930>)]. 
 +  * A mouse model of DS showed selective loss of sodium current in the hippocampal γ-aminobutyric acid(GABA)–mediated inhibitory interneurons. Failure of inhibition leading to excitation is hence a potential pathogenetic mechanism in this mutation causing DS[(:cite:16921370>{{pubmed>16921370}})].
  
 ===== Outcome ===== ===== Outcome =====
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 ===== Epilepsy surgery ===== ===== Epilepsy surgery =====
 Andrade et al (2010)[(:cite:19919661>{{pubmed>19919661}})] reported two adults aged 19&34 with Dravet syndrome who were treated with thalamic deep brain stimulation (DBS) , where the 19yr old showed marked improvement over a 10yr follow up, while the other did not.Small case series have also reported that palliative epilepsy surgery including Vagal Nerve Stimulation (VNS) and corpus callosotomy (CC) can be effective at reducing seizure frequency in Dravet syndrome[(:cite:27465677>{{pubmed>long:27465677}})]. Andrade et al (2010)[(:cite:19919661>{{pubmed>19919661}})] reported two adults aged 19&34 with Dravet syndrome who were treated with thalamic deep brain stimulation (DBS) , where the 19yr old showed marked improvement over a 10yr follow up, while the other did not.Small case series have also reported that palliative epilepsy surgery including Vagal Nerve Stimulation (VNS) and corpus callosotomy (CC) can be effective at reducing seizure frequency in Dravet syndrome[(:cite:27465677>{{pubmed>long:27465677}})].
 +
 +The presumed topography of the epileptogenic areas involves preferentially the mesial frontal lobe, the central area, sometimes the parietal and, even, the occipital lobes. Few interictal foci are localized in the temporal area. Surprisingly a hippocampal sclerosis has not been shown in the MRI of these patients who had prolonged and repeated severe FS[(:ref:todo)].
 ===== Cannabidiol ===== ===== Cannabidiol =====
   * Clinical trials show that cannabidiol reduces the number of convulsive and non-convulsive seizures when compared with usual care[(:cite:28813226>{{pubmed>28813226}})][(:cite:32040850>{{pubmed>32040850}})].   * Clinical trials show that cannabidiol reduces the number of convulsive and non-convulsive seizures when compared with usual care[(:cite:28813226>{{pubmed>28813226}})][(:cite:32040850>{{pubmed>32040850}})].
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 There is a wide variation among the phenotypes in these conditions and is possibly due to the strong influence of the genetic background. There is a wide variation among the phenotypes in these conditions and is possibly due to the strong influence of the genetic background.
  
-===== Classification ===== +===== References ===== 
-Dravet syndrome is classified under Electroclinical syndromes in the Revised ILAE Classification and Terminology (2010). In the majority of cases, no etiology has been found. A mitochondrial cytopathy has been reported in rare cases.+~~REFNOTES~~ 
  
-The presumed topography of the epileptogenic areas involves preferentially the mesial frontal lobe, the central area, sometimes the parietal and, even, the occipital lobes. Few interictal foci are localized in the temporal area. Surprisingly a hippocampal sclerosis has not been shown in the MRI of these patients who had prolonged and repeated severe FS. 
  
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