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Electroencephalographic features of patients with SCN1A-positive Dravet syndrome
Brain & Development 37 (2015) 599–611 www.elsevier.com/locate/braindev
Original article
Electroencephalographic features of patients with SCN1A-positive Dravet syndrome Hsiu-Fen Lee a,c, Ching-Shiang Chi b,c,⇑, Chi-Ren Tsai a,d, Chin-Hsuan Chen a, Chi-Chao Wang b a Department of Pediatrics, Taichung Veterans General Hospital, Taichung, Taiwan Department of Pediatrics, Tungs’ Taichung Metroharbor Hospital, Taichung, Taiwan c School of Medicine, Chung Shan Medical University, Taichung, Taiwan d Institute of Molecular Biology, National Chung Hsing University, Taichung, Taiwan
b
Received 30 June 2014; received in revised form 13 September 2014; accepted 3 October 2014
Abstract Objective: The aim of this study was to characterize the awake EEG features of patients with SCN1A-positive Dravet syndrome. Methods: Between January 2002 and December 2012, clinical data of 37 SCN1A-positive Dravet syndrome patients were collected. The first interictal awake EEG features, hot water bath test induced ictal seizure patterns and the concomitant EEG results, as well as follow-up interictal awake EEG recordings were analyzed. Results: Thirty-seven interictal awake EEG recordings showed 43.2% had normal features, 43.2% had nonspecific findings, and 13.5% had abnormal epileptiform discharges. Ictal pleomorphic seizure types with a median number of three were recorded in 26 patients. In total, 42.3% exhibited myoclonic seizures as their first recognizable seizure type with simultaneous EEG findings characterized by generalized or focal spikes, generalized 2–3.5 Hz spike and wave discharges, or generalized 2–3 Hz high voltage slow waves, and 30.8% manifested atypical absence seizures with concomitant EEG results showing generalized or focal spikes. Fifteen patients had 45 follow-up interictal awake EEGs during a period of six years. The follow-up awake EEG recordings revealed 42.2% had normal features, 42.2% showed nonspecific findings, and 15.6% disclosed epileptiform discharges. Conclusions: The initial and follow-up interictal awake EEG recordings showed normal results and nonspecific features in the majority of SCN1A-positive Dravet syndrome patients. Ictal electroencephalographic seizure types and concomitant EEG pictures were quite diverse and polymorphous. A low detection rate of interictal epileptiform abnormalities at awake stage might make patient management more challenging. Ó 2014 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.
Keywords: Dravet syndrome; EEG; SCN1A
1. Introduction Dravet syndrome (DS) was first described by Charlotte Dravet in 1978 [1] and was initially termed “severe
myoclonic epilepsy in infancy”. In 1989, the Commission on Classification and Terminology of the International League Against Epilepsy (ILAE) recommended the eponym “Dravet syndrome” instead because
⇑ Corresponding author at: Department of Pediatrics, Tungs’ Taichung Metroharbor Hospital, 699, Taiwan Boulevard Sec. 8, Wuchi, Taichung 435, Taiwan. Tel.: +886 4 2658 1919; fax: +886 4 2658 1155. E-mail address: [email protected] (C.-S. Chi).
http://dx.doi.org/10.1016/j.braindev.2014.10.003 0387-7604/Ó 2014 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.
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myoclonic seizures could be absent, and this epilepsy syndrome is not limited to infancy and childhood [2]. In 2001, the ILAE proposed that DS was an intractable form of epilepsy and classified it as an “epileptic encephalopathy”, assuming that the epileptiform abnormalities themselves might contribute to progressive dysfunction [3]. A decade later, this concept was demonstrated in the literature [4–6]. DS has been suggested to belong to the most severe end of the generalized epilepsy with febrile seizures plus spectrum [7–9], which is a group of clinically defined epilepsy syndromes associated with fever sensitivity in infancy and childhood. The typical DS is characterized by prolonged febrile and afebrile generalized and/or unilateral clonic or tonic-clonic seizures that occur in the first year of life in an otherwise normal infant. Subsequently, between one and four years of age, the condition evolves to other type of seizures such as myoclonic seizures, atypical absence seizures, complex partial seizures, and frequent status epilepticus. Developmental delay may become evident during the second year of life and is followed by motor impairment, cognitive dysfunction, and behavioral problems [10]. The provoking factors of slight body temperature variation, absence of true fever, and infections are characteristic and present throughout an epileptic’s life-span. Many other stimuli may trigger seizures: hot water bath, immunization, physical exercise, noisy environment, emotions, photo- and pattern sensitivity, and other individual stimuli [10,11]. In 2001, the discovery of SCN1A mutations in most affected patients led to designation of the syndrome as a disease, a channelopathy, and SCN1A was identified as a major causative gene for DS [12–15]. The SCN1A gene encodes the a1 subunit of the neuronal voltagegated sodium channel, Nav1.1, which is located on chromosome 2 at position 2q24.3. Mutations in patients with SCN1A-positive DS tend to be more deleterious (nonsense, truncating, or frameshift mutation) resulting in a loss or gain of function [16]. Animal models also suggest that the primary effects of DS SCN1A mutations result in interneuron dysfunction, or “interneuronopathy”, and decreased activity of GABAergic inhibitory neurons is likely to be a major factor contributing to seizure generation [16,17]. To date, various SCN1A mutations relevant to DS have been identified and many novel SCN1A mutations were reported in different countries [18–22]. Compared with clinical manifestations and SCN1A genetic features in DS patients reported in the literature, there are relatively limited reports focusing on electroencephalographic (EEG) findings in DS [23–26]. In this study, we analyzed the awake EEG findings of 37 SCN1A-positive DS patients. Twenty-six patients exhibiting hot water bath test (HWBT) induced ictal electroencephalographic seizure patterns were noted.
2. Materials and methods 2.1. Clinically presumptive diagnosis The following clinical characteristics were used to bolster a presumptive diagnosis of DS in our case series: (1) seizures beginning in the first year of life and normal development before the onset of seizures; (2) clinically pleomorphic seizure types, including a characteristic history of febrile, afebrile, and/or slight rise in body temperature around 37–37.9 °C with related generalized and/or unilateral clonic or tonic-clonic seizures and/or status epilepticus, alternating hemiconvulsive seizures, myoclonic seizures, atypical absence seizures, and/or partial seizures; (3) precipitating factors for seizures of fever, slight body temperature variation, immunization, and/or hot water bath; (4) probably noticeable motor regression after the age of 2 years with the appearance of ataxia and/or pyramidal signs accompanying cognitive impairment and behavior problems; (5) probably normal interictal EEG findings and initially normal brain MRI results. In our study, immunization-related seizure events in DS patients were restricted within an interval of 7 days between immunization and the occurrence of seizures. 2.2. Video EEG recording All patients had routine 21-channel video EEG, which was performed using a Nihon Kohden EEG (EEG-2110, Japan), a Nicolet vEEG (Viasys, USA), or a Comet AS-40 EEG (Grass, USA). Silver–silver chloride electrodes were positioned according to the International 10–20 System. All EEGs were recorded in stages of wakefulness. Intermittent photic stimulation (IPS) was performed in all patients. The distance between the eyes and the photic stimulator measured 30 cm. Flashes were delivered for 10 s for each frequency with intervals of 10 s. The frequency of the flashes was gradually increased from 1, 3, 6, 9, 12, 15, 18, 21, 24 to 27 Hz flashes. During the 10-s stimulation, the eyes were initially open. After 5-s stimulation, the patient was asked to close their eyes and keep them closed until the stimulation ceased. If patients were not able to cooperate with the instructions, the 10-s stimulation was performed with eyes open initially with or without spontaneous eye closing. Epileptic seizures were categorized based on the Classification of the ILAE of 1981. Interictal EEGs were used to assess background activity and paroxysmal abnormalities, such as diffuse or focal slowing, and focal or generalized epileptiform discharges. Video EEG recording during HWBT [27] was performed after obtaining informed consent from the patients’ parents. After a 20-min routine EEG recording, the patient was requested to remove his or her clothing and then sit in a small plastic bath tub with his or her
H.-F. Lee et al. / Brain & Development 37 (2015) 599–611
chest above the level of the water. The initial water temperature was around 35–37 °C depending on the patient’s preference. Hot water at a temperature of around 55–60 °C was collected in a stainless wash basin. The water temperature of the bath tub was increased gradually by means of alternately scooping water out of the bath tub and transferring hot water from the wash basin to the bath tub to raise the water temperature up to a maximum of around 40 °C. Simultaneously, water from the bath tub was intermittently poured onto the patient’s shoulders with a small bowl in order to elevate the patient’s body temperature. The patient’s axillary temperature and the water temperature were recorded simultaneously every 10 min during the course of the test. The procedure was discontinued immediately after seizure initiation. In cases where the patient exhibited a seizure during the test, he or she was taken out of the water, placed on a bed, gently dried with a towel, and seizure patterns were then recorded. If no seizure developed, the HWBT was ended after 30 min, and the final axillary and water temperatures were recorded. 2.3. Molecular analysis Genomic DNA was extracted from peripheral blood samples. All the exons of the SCN1A gene were amplified by polymerase chain reaction (PCR) with their corresponding intronic primers [28,29]. PCR products were subjected to bidirectional sequencing using a Big-Dye Terminator v3.1 Cycle Sequencing Kit and an ABI Prism 3100 genetic analyzer (Applied Biosystems, Foster City, CA). The protein sequence was based on ENSEMBL ENST00000423058. Written informed consent was obtained from all participants’ parents prior to collection of blood samples for molecular studies. 2.4. Data collection Fifty-one patients who were clinically diagnosed with DS were enrolled. Thirty-seven patients were confirmed to be carrying SCN1A mutations between January 2002 and December 2012. Clinical data of 37 SCN1A-positive DS patients, including gender, age at seizure onset, epileptic phenotypes, and trigger factors for seizures, were collected from all patients’ parents. Detailed physical examinations and neurologic evaluations were performed, and developmental milestones or cognitive functions were assessed as well. Patients younger than 5 years of age who were 3 months, 4–6 months, or more than 6 months behind normal developmental milestones were classified as mild, moderate, and severe developmental delay, respectively. In patients aged older than 5 years, the cognitive function was scored by intelligence quotient test [Wechsler Intelligence Scale for ChildrenRevised (WISC-R)]. The initial interictal awake EEG findings, and ictal seizure patterns, as well as the
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concomitant EEG results during HWBT were analyzed. Cases with follow-up awake EEG results were also analyzed. This study was approved by the Institutional Review Board (IRB TCVGH No. CF 13054). 3. Results 3.1. Study sample Demographic data, seizure characteristics, precipitating factors for seizures, family histories, medications, and development or intelligence assessments of 37 SCN1A-positive DS patients, 21 males and 16 females, are shown in Table 1. The median age at seizure onset was 6 months, ranging from 2 to 11 months. The median age of patients was 10 years and 11 months, ranging from 2 years and 9 months to 26 years and 5 months. Our patients manifested multiple seizure types with a median number of six types, ranging from three to eight. In total, 75.7% of patients exhibited myoclonic seizures. Trigger factors for seizures appeared in more than 50% of the patients, including fever, slight body temperature variation, hot water bath, and/or immunizations. Among 19 patients with seizures following immunization, 15 (78.9%) manifested seizures after DTP vaccines, 11 (57.9%) had a seizure in the context of elevated body temperature or fever, and 13 (68.4%) exhibited immunization-related seizures as the first clinical manifestation of DS, with a median interval between immunization and seizure of 24 h. A total of 22 vaccinations preceding seizure events occurred in 19 patients, including Diphtheria, Tetanus, and Pertussis (DTP) vaccine (15/22), Japanese encephalitis (JE) vaccine (4/22), Hepatitis B vaccine (1/22), rotavirus vaccine (1/22), and pneumococcus vaccine (1/22). Three cases, 19, 25, and 29 (3/ 19; 15.8%), experienced two immunization-related seizure events. Regarding the medications, 26 patients (70.2%) had more than three traditional antiepileptic drugs, and 10 (27.0%) received Stiripentol as an addon therapy. In addition, 27 patients (73.0%) manifested moderate to severe developmental delay or moderate to profound mental retardation. Table 2 shows the 37 heterogeneous SCN1A gene mutations. Fourteen mutations (37.8%) were classified as truncations (nine nonsense and five frameshift mutations), 18 (48.6%) were classified as missense mutations, and five (13.5%) were splice mutations. Truncating mutations spanned the whole span of subunits of the SCN1A protein. Among 37 identified SCN1A gene mutations, 22 (59.5%) belonged to novel mutations based on the genome databases. For truncating mutations and splice mutations, three genome databases, including the single nucleotide polymorphism database 141 (dbSNP141), gene ontology exome sequencing project (GO ESP) and 1000 Genomes, were searched, and
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Table 1 Demographic data of 37 patients with SCN1A-positive Dravet syndrome.
missense variations, and the results indicated deleterious mutations.
SCN1A-positive Dravet syndrome
Total number, N = 37
3.2. EEG findings
Gender, M:F Age at seizure onset, median (range)
21:16 6 mo (2 mo–11 mo) 6 (3–8)
Table 3 shows the interictal awake EEG findings, HWBT induced ictal seizure types, and concomitant epileptiform discharges. The median age of the first awake EEG recording was 1 year and 11 months, ranging from 5 months to 7 years and 4 months. The results of 37 interictal awake EEG recordings showed 16 patients (43.2%) exhibited normal features, 16 (43.2%) manifested nonspecific findings, i.e., background slowing or fast background activities, and 5 (13.5%) had generalized and/or focal spikes, or focal sharp waves. Thirty patients underwent the HWBT. The median body temperature was 37.8 °C, ranging from 36.8 to 38.7 °C, and the median water temperature was 39.0 °C, ranging from 37.9 to 40.0 °C. Ictal pleomorphic seizure types and concomitant EEG findings were recorded in 26 patients. During the period of video EEG recording, the first recognized clinical seizure types were as follows: 11 (42.3%) exhibited isolated or groups of brief bursts of symmetric or migrating, conspicuous or inconspicuous, myoclonic seizures, and the concomitant EEG findings were generalized or focal spikes, generalized 2–3.5 Hz spike and wave discharges, or generalized 2–3 Hz high voltage slow waves; 8 (30.8%) manifested atypical absence seizures associated with moderate impairment of consciousness, with or without myoclonic seizures, and the simultaneous EEG recordings were generalized or focal spikes (Fig. 1); four (15.4%) had generalized clonic or tonic-clonic seizures; two (7.8%) had focal seizures with clinical features of unilateral motor seizures; one (3.8%) had complex partial seizures, the main features of which were eye deviation, eyelid jerking, pallor, lip cyanosis, drooling, discrete oral automatisms, limb automatisms, and/or distal myoclonic jerks, and the EEG findings were characterized by generalized 3–3.5 Hz spike and wave discharges. The median number of ictal seizure types was three, ranging from one to five. The median duration of seizure events during the HWBT was 2 min and 18 s, ranging from 51 s to 36 min. Cases 11, 21, and 23 exhibited seizures longer than 15 min. Four patients, cases 27–30, showed neither HWBT induced ictal electroencephalographic seizure patterns nor specific epileptiform discharges on interictal awake EEG recordings. Fifteen patients had 45 follow-up interictal awake EEGs at various times between September 2007 and August 2013. The results of follow-up awake EEG recordings revealed 19 (42.2%) were normal features, 19 (42.2%) were nonspecific findings, including generalized background slowing, intermittent polymorphic background slowing, or excess fast activities, and 7 (15.6%) were focal spikes or generalized 2–2.5 Hz spike
Number of seizure types, median (range) Seizure characters GCs/GTCs, n (%) Complex partial seizure, n (%) Alternating hemiconvulsive seizure, n (%) Atypical absence seizure, n (%) Myoclonic seizure, n (%) Febrile status epilepticus, n (%) Partial seizures evolving into secondary generalization, n (%) Nocturnal seizure, n (%) Precipitating factors Fever, n (%) Elevated body temperature, n (%) Hot water bath, n (%) Vaccination, n (%) Hepatitis B vaccine DTP vaccine JE vaccine Rotavirus vaccine Photosensitivity, n (%) Physical exercise, n (%) Family history Epilepsy, n (%) Febrile seizure, n (%) Epilepsy and febrile seizure, n (%) Medications Traditional antiepileptic drugs (AEDs)c 1 AED, n (%) 2 AEDs, n (%) 3 AEDs, n (%) 4 AEDs, n (%) Stiripentol, n (%) Development or intelligence assessments Normal, n (%) Mild DD or mild MR, n (%) Moderate DD or moderate MR, n (%) Severe DD or severe MR, n (%) Profound MR, n (%)
33 33 32 28 28 24 20
(89.2) (89.2) (86.5) (75.7) (75.7) (64.9) (54.1)
14 (37.8) 37 (100) 37 (100) 25 (67.6) 19 (51.4) 1 15a 2 1b 13 (35.1) 12 (32.4) 2 (5.4) 3 (8.1) 1 (2.7)
4 (10.8) 7 (18.9) 16 (43.2) 10 (27.0) 10 (27.0) 2 (5.4) 8 (21.6) 9 (24.3) 12 (32.4) 6 (16.2)
DD, developmental delay; DTP vaccine, Diphtheria, Tetanus, and Pertussis vaccine; GCs, generalized clonic seizures; GTCs, generalized tonic-clonic seizures; JE vaccine, Japanese encephalitis vaccine; mo, months; MR, mental retardation; n, numbers. a Two cases 19 and 25 exhibited seizures while receiving the third dose of DTP vaccine at 6 months of age and the first dose of JE vaccine at 15 months of age. b Case 29 manifested seizures while receiving rotavirus vaccine at 4 months of age and pneumococcus vaccine at 14 months of age. c Traditional antiepileptic drugs include Clobazam, Clonazepam, Levetiracetam, Sodium valproate, or Topiramate.
there were no reported SNPs related to the novel mutations in our study. We also used two tools of polymorphism phenotyping v2 (PolyPhen-2) and sorting intolerant from tolerant (SIFT) to analyze these
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Table 2 SCN1A gene mutations of 37 patients with Dravet syndrome. SCN1A Case
Type of mutation
Exon
Amino acid changea
Location in protein
Novel mutation [ref]
34 9 13 8 20 27 1 5 31 35 26 36 16 21 7 33 22 17 2 12 15 32 30 37 4 11 10 14 28 25 23 6 3 19 24 29 18
Nonsense mutation Nonsense mutation Nonsense mutation Nonsense mutation Nonsense mutation Nonsense mutation Nonsense mutation Nonsense mutation Nonsense mutation Frameshift mutation Frameshift mutation Frameshift mutation Frameshift mutation Frameshift mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Splice mutation Splice mutation Splice mutation Splice mutation Splice mutation
1 5 5 11 11 11 12 12 15 2 6 6 25 26 2 2 5 5 5 9 9 15 20 20 21 21 22 22 23 25 26 26 Intron Intron Intron Intron Intron
R19X R222X R222X R613X R542X R542X Q711X R712X R862X I91fs I264fs D313fs S1615fs K1846fs R101Q L93S D194A K225N Y317H R393C S243F R946C R1322I K1313I C1354Y V1390M K1432R A1441T Q1450P V1612I R1642M I1683T IVS 1 +G > C IVS 4 +1G > A IVS 15 –4 12 del IVS 21-1 G > A IVS 24+5 G > C
N-terminal D1S4 D1S4 L1 L1 L1 L1 L1 D2S4 N-terminal D1S5 D1/S5–S6 D4S3 C-terminal N-terminal N-terminal D1S3 D1S4 D1/S5–S6 D1/S5–S6 D1S6 D2/S5–S6 D3S4 D3S4 D3S5 D3/S5–S6 D3/S5–S6 D3/S5–S6 D3/S5–S6 D4S3 D4S4 D4S5 N-terminal D1S2 D2S6 D3/S4–S5 L3
Yes No [18] No [18] No [18] No [18] No [18] Yes No [18] No [19] Yes Yes Yes Yes No [18] No [18] Yes Yes Yes Yes No [18] Yes No [18] Yes Yes Yes No [20] Yes Yes Yes No [21] Yes No [18] Yes No [22] Yes Yes Yes
1 4 15 21 24
The neuronal voltage-gated sodium-channel a-subunit (SCN1A) is organized in four homologous domains (D1–D4), each of which contain six transmembrane a helices (S1–S6) and an additional pore loop (L) located between the S5 and S6 segments, plus a carboxy terminus (C-terminal), and a amino terminus (N-terminal). [ref], [reference]. a Protein sequence of SCN1A was based on ENSEMBL ENST00000423058.
and wave discharges. Focal spikes were located on the frontal and temporal areas with frontal predominance. 4. Discussion The first interictal awake EEG recordings in SCN1Apositive DS showed that 86.4% of patients exhibited nonspecific features and 13.5% had epileptiform discharges at the median age of 1 year and 11 months. None of our cases exhibited electric photosensitivity despite the fact that clinical photosensitivity was 35.1%. Both of these observations were in contrast to previous studies that reported epileptiform abnormalities in the progression of EEG features became evident in 59–77% of DS patients during the second year of life
[24], and generalized photoparoxysmal responses (PPR) during IPS were reported in at least 40% of DS cases which would reinforce the diagnosis [24–26]. Our observation of a low rate of interictal epileptiform discharges and no elicitation of PPR during IPS might be for some limitations. The first one was that our patients were present to our hospitals at various first-visit ages with a range of 5 months to 7 years and 4 months, and some patients received medications before, both of which might influence the results of the interictal EEG recordings at the time of examinations. The second was our first interictal EEG studies were only recorded in the awake stage for the following HWBT, and the results of EEG findings could be more informative if sleep EEG recordings were performed. The third was that a
Case
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Table 3 EEG findings of patients with SCN1A-positive Dravet syndrome. Age
Age at Sz onset
The first EEG recording Age
Interictal EEG
Ictal EEG
Simultaneous ictal seizure patterns
Duration
1
F
25y 3mo
6mo
3y
Gen. spikes ! MCA
MS ! AAS ! GTCS
1 min 35 s
2
F
12y 3mo
10mo
2y 1mo
11 min
M M
8y 7mo 13y 11mo
2mo 6mo
8mo 7y 4mo
Gen. spikes ! polymorphic background slowing Gen. 2–3 Hz high voltage slow waves Gen. spikes ! MCA
MS ! GCS ! CPS
3 4
MS, migrating MS ! GTCS
8 min 1 min 2 s
5
M
7y
3mo
7mo
Background slow Background slow Normal Background slow Normal
MS ! focal Sz ! GTCS ! CPS
4 min 46 s
6 7
F M
8y 11mo 5y 7mo
2mo 6mo
3y 2mo 2y 2mo
MS ! focal Sz ! GTCS ! GCS ! CPS MS ! focal Sz ! GCS
1 min 14 s 1 min
8 9 10 11 12
F F F M M
3y 8mo 6y 2mo 5y 8mo 2y 9mo 12y 9mo
6mo 9mo 6mo 4mo 2mo
1y 3mo 3y 9mo 3y 4mo 8mo 2y 9mo
MS ! focal Sz ! GTCS MS ! CPS ! focal Sz ! GTCS MS ! focal Sz ! GTCS MS ! SPS and MS AAS ! MS ! focal Sz ! GCS ! CPS
2 min 16 s 2 min 2 min 28 min 23 s 1 min 57 s
13
M
10y 10mo
7mo
1y 3mo
AAS ! MS ! focal Sz ! MS ! CPS
51 s
14
F
14y 5mo
4mo
5y 10mo
Gen. 2–2.5 Hz SWD ! MCA Gen. 3–3.5 Hz SWD ! Gen. spikes ! MCA Gen. spikes ! MCA Gen. spikes ! focal spikes and polyspikes Gen. spikes ! MCA ! Gen.3–4 Hz SWD and spikes Focal spikes ! Gen. spikes ! focal spikes ! Gen. spikes Focal spikes ! GED ! MCA
AAS ! focal Sz ! GTCS
1 min 9 s
15
F
7y 11mo
6mo
11mo
Focal spikes ! GED
AAS ! MS ! CPS ! focal Sz ! CPS
2 min 16 s
16
M
6y 2mo
6mo
1y 1mo
AAS ! CPS ! MS
2 min 30 s
17
M
8y 9mo
6mo
4y
Focal spikes ! Gen. 2.5–3 Hz SWD ! focal spikes GED ! MCA
AAS ! GCS ! focal Sz
2 min 34 s
18 19
F F
11y 1mo 7y
5mo 2mo
6y 6mo 2y 10mo
AAS ! CPS AAS ! focal Sz ! GCS ! MS, migrating
2 min 3 min 30 s
20
F
10y 3mo
7mo
1y 9mo
Focal spikes ! Gen. spikes ! focal spikes Focal spikes ! Gen. 3–3.5 Hz SWD ! MCA ! Gen. spikes MCA ! Gen. spikes
GCS ! focal Sz ! MS
1 min 58 s
21 22
M M
13y 2mo 23y 9mo
2mo 4mo
8mo 6y 3mo
MCA MCA
GTCS GTCS
33 min 2 min 20 s
23 24
M M
17y 5mo 10y 11mo
6mo 8mo
1y 4mo 2y 1mo
MCA MCA ! Gen. 2–3 Hz SWD ! Gen. spikes
GTCS Focal Sz ! GTCS ! MS ! Focal Sz
36 min 5 min 22 s
25
F
8y 8mo
6mo
9mo
Focal sharp waves ! Gen. 4–5 Hz SWD ! focal spikes
Focal Sz ! CPS ! MS ! CPS ! GTCS
2 min 24 s
Excess fast Background slow Normal Gen. spikes Normal Normal Background slow Gen. spikes Focal/Gen. spikes Background slow Normal Background slow Focal spikes Background slow Background slow Normal Background slow Normal Background slow Focal sharp waves
Gen. 2.5–3 Hz SWD ! Gen. 1–2 Hz SWD ! MCA Focal spikes ! GED ! MCA Focal spikes ! GED
H.-F. Lee et al. / Brain & Development 37 (2015) 599–611
Gender
Gen. 3–3.5 Hz SWD ! focal spikes ! Gen. spikes ! GED Not detected
CPS ! AAS ! focal Sz ! GTCS
10 min 17 s
Not detected
Not detected
Not detected
10mo
Background slow Normal
Not detected
Not detected
3mo
3y 3mo
Excess fast
Not detected
Not detected
18y 1mo
11mo
11mo
Normal
Not done
Not available
F
26y 4mo
5mo
5mo
Normal
Not done
Not available
33
M
25y 2mo
9mo
9mo
Normal
Not done
Not available
34
M
26y 5mo
6mo
11mo
Not done
Not available
35
F
16y 7mo
5mo
5mo
Background slow Normal
Not done
Not available
36
F
15y 8mo
6mo
6mo
Normal
Not done
Not available
37
F
5y
8mo
3y 8mo
Normal
Not done
Not available
Not available Not available Not available Not available Not available Not available Not available Not available Not available Not available Not available
M
13y 11mo
5mo
5y 2mo
27
M
13y 8mo
5mo
3y 7mo
28
M
11y 10mo
8mo
1y 11mo
29
M
6y 7mo
4mo
30
M
7y 9mo
31
M
32
AAS, atypical absence seizure; CPS, complex partial seizure; F, female; GCS, generalized clonic seizure; GED, generalized epileptiform discharges; Gen., generalized; GTCS, generalized tonic-clonic seizure; MCA, muscle contraction artifact; mo, months; MS, myoclonic seizures; SPS, simple partial seizure; SWD, spike and wave discharges; Sz, seizure; y, years.
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Background slow Normal
26
605
606
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Fig. 1. Pleomorphic ictal electroencephalographic seizure patterns of case 19, aged 2 years and 10 months. (A) Before the hot water bath test (HWBT), the interictal EEG shows slowing background activity. (B) 14 min and 15 s after starting the HWBT, she exhibits clinical features of intermittent eye staring and dreaming. Initial duration of each episode is one to two seconds followed by longer durations intermittently, with longest duration of 10 s. The EEG recording shows focal spikes arising from the right hemisphere followed by generalized 3–3.5 Hz spike and wave discharges. (C) Sudden motionless, eye staring, yelling, eye deviation to the left side followed by generalized clonic seizures and lip cyanosis develop, lasting around 30 s. The simultaneous body and water temperatures are 37.8 and 39 °C, respectively. The EEG recording reveals muscle contraction artifact. (D–E) Evolution into migrating myoclonus occurs later on. The EEG recording shows generalized spike and wave discharges, and the density of epileptiform discharges decrease as the frequency and intensity of myoclonus lessen. The total duration is 70 s. (F) Post-ictal phase is characterized by eye opening and lying motionless, and the EEG trace shows a flat background activity. (G) Post-ictal phase reveals sleepiness, and the EEG trace shows slowing background activity.
discrepancy between laboratory EEGs’ photosensitivity and everyday clinical sensitivity to light has been reported to occur in DS patients [30]. Taken together, the interictal awake EEG features in our case series revealed that the majority of cases had normal results, slowing background activities or fast waves, and there was a low detection rate of abnormal epileptiform discharges and PPR at IPS. We suggest that normal and/ or nonspecific interictal awake EEG features are indicative of limit value. The accurate diagnosis of DS remains fundamentally reliant on clinical characteristics of seizure type and genetic analyses [31,32]. Ictal electroencephalographic recordings induced by HWBT were very different and polymorphous. We observed that the median number of evolutionary seizure types was three. Regarding the first recognized seizure type, the most common seizure semiology was myoclonic seizure. Myoclonic seizures in DS have been reported to be heterogeneous and include epileptic or nonepileptic myoclonus [26]. The concomitant EEG findings of myoclonic seizures could show generalized
or multiple spike and wave discharges, at 3 Hz or more [26], which were similar to our results of generalized or focal spikes, generalized 2–3.5 Hz spike and wave discharges or generalized 2–3 Hz high voltage slow waves. The most common seizure type following initiation of myoclonic seizure was unilateral focal motor seizure in 5 of the 11 patients. An exception was case 3, who presented with migrating myoclonic seizures as his sole clinical seizure type during the course of recording. The second most common first-recognized ictal seizure type was atypical absence seizure. Atypical absence seizures have been proposed to be classified into atypical absence seizures with impaired consciousness only and those with myoclonic component [26]. In both seizure types, the EEG recording might show generalized irregular spikes and waves at 2–3.5 Hz, and the myoclonic seizures might be very mild and isolated during the spike and wave bursts [26]. Our case series also showed that 5 of 8 patients who presented with atypical absence seizures as their first ictal seizure type exhibited myoclonic seizures either as the coming seizure type or as one of
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Fig. 1 (continued)
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Fig. 1 (continued)
multiple evolutionary seizure patterns. Case 19 demonstrated atypical absence seizure and myoclonic seizure occurred separately between polymorphic seizure types.
A previous report showed that unilateral motor seizures were usually long-lasting in DS and might constitute an epileptic status [31]. Our study revealed one patient, case
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Fig. 1 (continued)
11, with seizure duration longer than 15 min actually exhibited myoclonic seizures preceded by simple partial motor seizures, which are rarely described in the
literature [24,26]. Tonic seizure was not identified in our case series, which was consistent with results reported in the literature [26]. We conclude that the ictal
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electroencephalographic findings during HWBT in patients with SCN1A-positive DS appear to be widely diverse. However, a limitation in our study was that the absence of ictal EEG findings of unprovoked habitual seizures could be comparable with those of hot water bath induced seizures. Given that both the appearance of clinical features and EEG recordings of DS are age-dependent, a definite diagnosis can usually be made based on the presence of all the symptoms and confirmation by comprehensive electroclinical studies until early childhood. Nevertheless, our study showed in a six-year follow-up of interictal awake EEG features that there were no significant changes, i.e., 86.4% of initial awake EEGs vs. 84.4% of follow-up awake EEGs showing nonspecific findings, and 13.5% of initial awake EEGs vs. 15.6% of follow-up awake EEGs revealing abnormal epileptiform discharges. We suggest that routine follow-up awake EEGs should not be repeated very often. In conclusion, the first and follow-up interictal awake EEG recordings in the majority of SCN1A-positive DS patients disclosed normal results and nonspecific findings. There was a discrepancy between the two EEG results for photosensitivity and clinical sensitivity to light. Ictal electroencephalographic seizure types and concomitant EEG recordings were diverse and polymorphous, in which myoclonic seizures and atypical absence seizures were the two most common recognized ictal seizure types. A low rate of interictal awake epileptiform abnormalities might make patient management more challenging.
Acknowledgements Funding for this study was supported by Taichung Veterans General Hospital (TCVGH 926503C). References [1] Dravet C. Les epilepsies graves de le´nfant. Vie Med 1978;8:543–8. [2] Commission on Classification and Terminology of the International. League against epilepsy. Proposal for revised classification of epilepsies and epileptic syndromes. Epilepsia 1989;30: 389–99. [3] Engel Jr J, International League Against Epilepsy (ILAE). A proposed diagnostic scheme for people with epileptic seizures and with epilepsy: report of the ILAE task force on classification and terminology. Epilepsia 2001;42:796–803. [4] Ragona F, Granata T, Bernardina BD, Offredi F, Darra F, Battaglia D, et al. Cognitive development in Dravet syndrome: a retrospective, multicenter study of 26 patients. Epilepsia 2011;52: 386–92. [5] Ragona F. Cognitive development in children with Dravet syndrome. Epilepsia 2011;52(Suppl. 2):39–43. [6] Catarino CB, Liu JYW, Liagkouras I, Gibbons VS, Labrum RW, Ellis R, et al. Dravet syndrome as epileptic encephalopathy: evidence from long-term course and neuropathy. Brain 2011;134: 2982–3010.
[7] Scheffer IE, Berkovic SF. Generalized epilepsy with febrile seizures plus: a genetic disorder with heterogeneous clinical phenotypes. Brain 1997;120:479–90. [8] Singh R, Scheffer IE, Crossland K, Berkovic SF. Generalized epilepsy with febrile seizures plus: a common childhood-onset genetic epilepsy syndrome. Ann Neurol 1999;45:75–81. [9] Singh R, Andermann E, Whitehouse WPA, Harvey AS, Keene DL, Seni M-H, et al. Severe myoclonic epilepsy of infancy: extended spectrum of GEFS+? Epilepsia 2001;42: 837–44. [10] Dravet C, Bureau M, Oguni H, Fukuyama Y, Cokar O. Severe myoclonic epilepsy in infancy (Dravet syndrome). In: Roger J, Bureau M, Dravet C, Genton P, Tassinari CA, Wolf P, editors. Epileptic syndromes in infancy, childhood and adolescence. United Kingdom: John Libbey & Co Ltd; 2002. p. 81–103. [11] Tro-Baumann B, von Spiczak S, Lotte J, Bast T, Haberlandt E, Sassen R, et al. A retrospective study of the relation between vaccination and occurrence of seizures in Dravet syndrome. Epilepsia 2011;52:175–8. [12] Claes L, Del-Favero J, Ceulemans B, Lagae L, Van Broeckhoven C, De Jonghe P. De novo mutations in the sodium-channel gene SCN1A cause severe myoclonic epilepsy of infancy. Am J Hum Genet 2001;68:1327–32. [13] Harkin LA, McMahon JM, Iona X, Dibbens L, Pelekanos JT, Zuberi SM, et al. The spectrum of SCN1A-related infantile epileptic encephalopathies. Brain 2007;130:843–52. [14] Escayg A, MacDonald BT, Meisler MH, Baulac S, Huberfeld G, An-Gourfinkel I, et al. Mutations of SCN1A, encoding a neuronal sodium channel, in two families with GEFS+2. Nat Genet 2000;24:343–5. [15] Volkers L, Kahlig KM, Verbeek NE, Das JHG, van Kempen MJA, Stroink H, et al. Nav1.1 dysfunction in genetic epilepsy with febrile seizure-plus or Dravet syndrome. Eur J Neurosci 2011;34:1268–75. [16] Morse RP. Dravet syndrome: inroads into understanding epileptic encephalopathies. J Pediatr 2011;158:354–9. [17] Escayg A, Goldin AL. Sodium channel SCN1A and epilepsy: mutations and mechanisms. Epilepsia 2010;51:1650–8. [18] Zuberi SM, Brunklaus A, Birch R, Reavey E, Duncan J, Forbes GH. Genotype-phenotype associations in SCN1A-related epilepsies. Neurology 2011;76:594–600. [19] Orrico A, Galli L, Grosso S, Buoni S, Pianigiani R, Balestri P, et al. Mutational analysis of the SCN1A, SCN1B and GABRG2 genes in 150 Italian patients with idiopathic childhood epilepsies. Clin Genet 2009;75:579–81. [20] Sun H, Zhang Y, Liu X, Ma X, Yang Z, Qin J, et al. Analysis of SCN1A mutation and parental origin in patients with Dravet syndrome. J Hum Genet 2010;55:421–7. [21] Kwong AKY, Fung CW, Chan SY, Wong VCN. Identification of SCN1A and PCDH19 mutations in Chinese children with Dravet syndrome. PLoS ONE 2012;7:e41802. [22] Rodda JM, Scheffer IE, McMahon JM, Berkovic SF, Graham HK. Progressive gait deterioration in adolescents with Dravet syndrome. Arch Neurol 2012;69:873–8. [23] Caraballo RH, Fejerman N. Dravet syndrome: a study of 53 patients. Epilepsy Res 2006;70:S231–8. [24] Specchio N, Balestri M, Trivisano M, Japaridze N, Striano P, Carotenuto A, et al. Electroencephalographic features in Dravet syndrome: five-year follow-up study in 22 patients. J Child Neurol 2012;27:439–44. [25] Arzimanoglou A. Dravet syndrome: from electroclinical characteristics to molecular biology. Epilepsia 2009;50(Suppl. 8):3–9. [26] Bureau M, Bernardina BD. Electroencephalographic characteristics of Dravet syndrome. Epilepsia 2011;52(Suppl. 2):13–23. [27] Ogino T. Severe myoclonic epilepsy in infancy – a clinical and electroencephalographic study (in Japanese). J Jpn Epil Soc 1986;4:114–26.
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Original article
Electroencephalographic features of patients with SCN1A-positive Dravet syndrome Hsiu-Fen Lee a,c, Ching-Shiang Chi b,c,⇑, Chi-Ren Tsai a,d, Chin-Hsuan Chen a, Chi-Chao Wang b a Department of Pediatrics, Taichung Veterans General Hospital, Taichung, Taiwan Department of Pediatrics, Tungs’ Taichung Metroharbor Hospital, Taichung, Taiwan c School of Medicine, Chung Shan Medical University, Taichung, Taiwan d Institute of Molecular Biology, National Chung Hsing University, Taichung, Taiwan
b
Received 30 June 2014; received in revised form 13 September 2014; accepted 3 October 2014
Abstract Objective: The aim of this study was to characterize the awake EEG features of patients with SCN1A-positive Dravet syndrome. Methods: Between January 2002 and December 2012, clinical data of 37 SCN1A-positive Dravet syndrome patients were collected. The first interictal awake EEG features, hot water bath test induced ictal seizure patterns and the concomitant EEG results, as well as follow-up interictal awake EEG recordings were analyzed. Results: Thirty-seven interictal awake EEG recordings showed 43.2% had normal features, 43.2% had nonspecific findings, and 13.5% had abnormal epileptiform discharges. Ictal pleomorphic seizure types with a median number of three were recorded in 26 patients. In total, 42.3% exhibited myoclonic seizures as their first recognizable seizure type with simultaneous EEG findings characterized by generalized or focal spikes, generalized 2–3.5 Hz spike and wave discharges, or generalized 2–3 Hz high voltage slow waves, and 30.8% manifested atypical absence seizures with concomitant EEG results showing generalized or focal spikes. Fifteen patients had 45 follow-up interictal awake EEGs during a period of six years. The follow-up awake EEG recordings revealed 42.2% had normal features, 42.2% showed nonspecific findings, and 15.6% disclosed epileptiform discharges. Conclusions: The initial and follow-up interictal awake EEG recordings showed normal results and nonspecific features in the majority of SCN1A-positive Dravet syndrome patients. Ictal electroencephalographic seizure types and concomitant EEG pictures were quite diverse and polymorphous. A low detection rate of interictal epileptiform abnormalities at awake stage might make patient management more challenging. Ó 2014 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.
Keywords: Dravet syndrome; EEG; SCN1A
1. Introduction Dravet syndrome (DS) was first described by Charlotte Dravet in 1978 [1] and was initially termed “severe
myoclonic epilepsy in infancy”. In 1989, the Commission on Classification and Terminology of the International League Against Epilepsy (ILAE) recommended the eponym “Dravet syndrome” instead because
⇑ Corresponding author at: Department of Pediatrics, Tungs’ Taichung Metroharbor Hospital, 699, Taiwan Boulevard Sec. 8, Wuchi, Taichung 435, Taiwan. Tel.: +886 4 2658 1919; fax: +886 4 2658 1155. E-mail address: [email protected] (C.-S. Chi).
http://dx.doi.org/10.1016/j.braindev.2014.10.003 0387-7604/Ó 2014 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.
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myoclonic seizures could be absent, and this epilepsy syndrome is not limited to infancy and childhood [2]. In 2001, the ILAE proposed that DS was an intractable form of epilepsy and classified it as an “epileptic encephalopathy”, assuming that the epileptiform abnormalities themselves might contribute to progressive dysfunction [3]. A decade later, this concept was demonstrated in the literature [4–6]. DS has been suggested to belong to the most severe end of the generalized epilepsy with febrile seizures plus spectrum [7–9], which is a group of clinically defined epilepsy syndromes associated with fever sensitivity in infancy and childhood. The typical DS is characterized by prolonged febrile and afebrile generalized and/or unilateral clonic or tonic-clonic seizures that occur in the first year of life in an otherwise normal infant. Subsequently, between one and four years of age, the condition evolves to other type of seizures such as myoclonic seizures, atypical absence seizures, complex partial seizures, and frequent status epilepticus. Developmental delay may become evident during the second year of life and is followed by motor impairment, cognitive dysfunction, and behavioral problems [10]. The provoking factors of slight body temperature variation, absence of true fever, and infections are characteristic and present throughout an epileptic’s life-span. Many other stimuli may trigger seizures: hot water bath, immunization, physical exercise, noisy environment, emotions, photo- and pattern sensitivity, and other individual stimuli [10,11]. In 2001, the discovery of SCN1A mutations in most affected patients led to designation of the syndrome as a disease, a channelopathy, and SCN1A was identified as a major causative gene for DS [12–15]. The SCN1A gene encodes the a1 subunit of the neuronal voltagegated sodium channel, Nav1.1, which is located on chromosome 2 at position 2q24.3. Mutations in patients with SCN1A-positive DS tend to be more deleterious (nonsense, truncating, or frameshift mutation) resulting in a loss or gain of function [16]. Animal models also suggest that the primary effects of DS SCN1A mutations result in interneuron dysfunction, or “interneuronopathy”, and decreased activity of GABAergic inhibitory neurons is likely to be a major factor contributing to seizure generation [16,17]. To date, various SCN1A mutations relevant to DS have been identified and many novel SCN1A mutations were reported in different countries [18–22]. Compared with clinical manifestations and SCN1A genetic features in DS patients reported in the literature, there are relatively limited reports focusing on electroencephalographic (EEG) findings in DS [23–26]. In this study, we analyzed the awake EEG findings of 37 SCN1A-positive DS patients. Twenty-six patients exhibiting hot water bath test (HWBT) induced ictal electroencephalographic seizure patterns were noted.
2. Materials and methods 2.1. Clinically presumptive diagnosis The following clinical characteristics were used to bolster a presumptive diagnosis of DS in our case series: (1) seizures beginning in the first year of life and normal development before the onset of seizures; (2) clinically pleomorphic seizure types, including a characteristic history of febrile, afebrile, and/or slight rise in body temperature around 37–37.9 °C with related generalized and/or unilateral clonic or tonic-clonic seizures and/or status epilepticus, alternating hemiconvulsive seizures, myoclonic seizures, atypical absence seizures, and/or partial seizures; (3) precipitating factors for seizures of fever, slight body temperature variation, immunization, and/or hot water bath; (4) probably noticeable motor regression after the age of 2 years with the appearance of ataxia and/or pyramidal signs accompanying cognitive impairment and behavior problems; (5) probably normal interictal EEG findings and initially normal brain MRI results. In our study, immunization-related seizure events in DS patients were restricted within an interval of 7 days between immunization and the occurrence of seizures. 2.2. Video EEG recording All patients had routine 21-channel video EEG, which was performed using a Nihon Kohden EEG (EEG-2110, Japan), a Nicolet vEEG (Viasys, USA), or a Comet AS-40 EEG (Grass, USA). Silver–silver chloride electrodes were positioned according to the International 10–20 System. All EEGs were recorded in stages of wakefulness. Intermittent photic stimulation (IPS) was performed in all patients. The distance between the eyes and the photic stimulator measured 30 cm. Flashes were delivered for 10 s for each frequency with intervals of 10 s. The frequency of the flashes was gradually increased from 1, 3, 6, 9, 12, 15, 18, 21, 24 to 27 Hz flashes. During the 10-s stimulation, the eyes were initially open. After 5-s stimulation, the patient was asked to close their eyes and keep them closed until the stimulation ceased. If patients were not able to cooperate with the instructions, the 10-s stimulation was performed with eyes open initially with or without spontaneous eye closing. Epileptic seizures were categorized based on the Classification of the ILAE of 1981. Interictal EEGs were used to assess background activity and paroxysmal abnormalities, such as diffuse or focal slowing, and focal or generalized epileptiform discharges. Video EEG recording during HWBT [27] was performed after obtaining informed consent from the patients’ parents. After a 20-min routine EEG recording, the patient was requested to remove his or her clothing and then sit in a small plastic bath tub with his or her
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chest above the level of the water. The initial water temperature was around 35–37 °C depending on the patient’s preference. Hot water at a temperature of around 55–60 °C was collected in a stainless wash basin. The water temperature of the bath tub was increased gradually by means of alternately scooping water out of the bath tub and transferring hot water from the wash basin to the bath tub to raise the water temperature up to a maximum of around 40 °C. Simultaneously, water from the bath tub was intermittently poured onto the patient’s shoulders with a small bowl in order to elevate the patient’s body temperature. The patient’s axillary temperature and the water temperature were recorded simultaneously every 10 min during the course of the test. The procedure was discontinued immediately after seizure initiation. In cases where the patient exhibited a seizure during the test, he or she was taken out of the water, placed on a bed, gently dried with a towel, and seizure patterns were then recorded. If no seizure developed, the HWBT was ended after 30 min, and the final axillary and water temperatures were recorded. 2.3. Molecular analysis Genomic DNA was extracted from peripheral blood samples. All the exons of the SCN1A gene were amplified by polymerase chain reaction (PCR) with their corresponding intronic primers [28,29]. PCR products were subjected to bidirectional sequencing using a Big-Dye Terminator v3.1 Cycle Sequencing Kit and an ABI Prism 3100 genetic analyzer (Applied Biosystems, Foster City, CA). The protein sequence was based on ENSEMBL ENST00000423058. Written informed consent was obtained from all participants’ parents prior to collection of blood samples for molecular studies. 2.4. Data collection Fifty-one patients who were clinically diagnosed with DS were enrolled. Thirty-seven patients were confirmed to be carrying SCN1A mutations between January 2002 and December 2012. Clinical data of 37 SCN1A-positive DS patients, including gender, age at seizure onset, epileptic phenotypes, and trigger factors for seizures, were collected from all patients’ parents. Detailed physical examinations and neurologic evaluations were performed, and developmental milestones or cognitive functions were assessed as well. Patients younger than 5 years of age who were 3 months, 4–6 months, or more than 6 months behind normal developmental milestones were classified as mild, moderate, and severe developmental delay, respectively. In patients aged older than 5 years, the cognitive function was scored by intelligence quotient test [Wechsler Intelligence Scale for ChildrenRevised (WISC-R)]. The initial interictal awake EEG findings, and ictal seizure patterns, as well as the
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concomitant EEG results during HWBT were analyzed. Cases with follow-up awake EEG results were also analyzed. This study was approved by the Institutional Review Board (IRB TCVGH No. CF 13054). 3. Results 3.1. Study sample Demographic data, seizure characteristics, precipitating factors for seizures, family histories, medications, and development or intelligence assessments of 37 SCN1A-positive DS patients, 21 males and 16 females, are shown in Table 1. The median age at seizure onset was 6 months, ranging from 2 to 11 months. The median age of patients was 10 years and 11 months, ranging from 2 years and 9 months to 26 years and 5 months. Our patients manifested multiple seizure types with a median number of six types, ranging from three to eight. In total, 75.7% of patients exhibited myoclonic seizures. Trigger factors for seizures appeared in more than 50% of the patients, including fever, slight body temperature variation, hot water bath, and/or immunizations. Among 19 patients with seizures following immunization, 15 (78.9%) manifested seizures after DTP vaccines, 11 (57.9%) had a seizure in the context of elevated body temperature or fever, and 13 (68.4%) exhibited immunization-related seizures as the first clinical manifestation of DS, with a median interval between immunization and seizure of 24 h. A total of 22 vaccinations preceding seizure events occurred in 19 patients, including Diphtheria, Tetanus, and Pertussis (DTP) vaccine (15/22), Japanese encephalitis (JE) vaccine (4/22), Hepatitis B vaccine (1/22), rotavirus vaccine (1/22), and pneumococcus vaccine (1/22). Three cases, 19, 25, and 29 (3/ 19; 15.8%), experienced two immunization-related seizure events. Regarding the medications, 26 patients (70.2%) had more than three traditional antiepileptic drugs, and 10 (27.0%) received Stiripentol as an addon therapy. In addition, 27 patients (73.0%) manifested moderate to severe developmental delay or moderate to profound mental retardation. Table 2 shows the 37 heterogeneous SCN1A gene mutations. Fourteen mutations (37.8%) were classified as truncations (nine nonsense and five frameshift mutations), 18 (48.6%) were classified as missense mutations, and five (13.5%) were splice mutations. Truncating mutations spanned the whole span of subunits of the SCN1A protein. Among 37 identified SCN1A gene mutations, 22 (59.5%) belonged to novel mutations based on the genome databases. For truncating mutations and splice mutations, three genome databases, including the single nucleotide polymorphism database 141 (dbSNP141), gene ontology exome sequencing project (GO ESP) and 1000 Genomes, were searched, and
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Table 1 Demographic data of 37 patients with SCN1A-positive Dravet syndrome.
missense variations, and the results indicated deleterious mutations.
SCN1A-positive Dravet syndrome
Total number, N = 37
3.2. EEG findings
Gender, M:F Age at seizure onset, median (range)
21:16 6 mo (2 mo–11 mo) 6 (3–8)
Table 3 shows the interictal awake EEG findings, HWBT induced ictal seizure types, and concomitant epileptiform discharges. The median age of the first awake EEG recording was 1 year and 11 months, ranging from 5 months to 7 years and 4 months. The results of 37 interictal awake EEG recordings showed 16 patients (43.2%) exhibited normal features, 16 (43.2%) manifested nonspecific findings, i.e., background slowing or fast background activities, and 5 (13.5%) had generalized and/or focal spikes, or focal sharp waves. Thirty patients underwent the HWBT. The median body temperature was 37.8 °C, ranging from 36.8 to 38.7 °C, and the median water temperature was 39.0 °C, ranging from 37.9 to 40.0 °C. Ictal pleomorphic seizure types and concomitant EEG findings were recorded in 26 patients. During the period of video EEG recording, the first recognized clinical seizure types were as follows: 11 (42.3%) exhibited isolated or groups of brief bursts of symmetric or migrating, conspicuous or inconspicuous, myoclonic seizures, and the concomitant EEG findings were generalized or focal spikes, generalized 2–3.5 Hz spike and wave discharges, or generalized 2–3 Hz high voltage slow waves; 8 (30.8%) manifested atypical absence seizures associated with moderate impairment of consciousness, with or without myoclonic seizures, and the simultaneous EEG recordings were generalized or focal spikes (Fig. 1); four (15.4%) had generalized clonic or tonic-clonic seizures; two (7.8%) had focal seizures with clinical features of unilateral motor seizures; one (3.8%) had complex partial seizures, the main features of which were eye deviation, eyelid jerking, pallor, lip cyanosis, drooling, discrete oral automatisms, limb automatisms, and/or distal myoclonic jerks, and the EEG findings were characterized by generalized 3–3.5 Hz spike and wave discharges. The median number of ictal seizure types was three, ranging from one to five. The median duration of seizure events during the HWBT was 2 min and 18 s, ranging from 51 s to 36 min. Cases 11, 21, and 23 exhibited seizures longer than 15 min. Four patients, cases 27–30, showed neither HWBT induced ictal electroencephalographic seizure patterns nor specific epileptiform discharges on interictal awake EEG recordings. Fifteen patients had 45 follow-up interictal awake EEGs at various times between September 2007 and August 2013. The results of follow-up awake EEG recordings revealed 19 (42.2%) were normal features, 19 (42.2%) were nonspecific findings, including generalized background slowing, intermittent polymorphic background slowing, or excess fast activities, and 7 (15.6%) were focal spikes or generalized 2–2.5 Hz spike
Number of seizure types, median (range) Seizure characters GCs/GTCs, n (%) Complex partial seizure, n (%) Alternating hemiconvulsive seizure, n (%) Atypical absence seizure, n (%) Myoclonic seizure, n (%) Febrile status epilepticus, n (%) Partial seizures evolving into secondary generalization, n (%) Nocturnal seizure, n (%) Precipitating factors Fever, n (%) Elevated body temperature, n (%) Hot water bath, n (%) Vaccination, n (%) Hepatitis B vaccine DTP vaccine JE vaccine Rotavirus vaccine Photosensitivity, n (%) Physical exercise, n (%) Family history Epilepsy, n (%) Febrile seizure, n (%) Epilepsy and febrile seizure, n (%) Medications Traditional antiepileptic drugs (AEDs)c 1 AED, n (%) 2 AEDs, n (%) 3 AEDs, n (%) 4 AEDs, n (%) Stiripentol, n (%) Development or intelligence assessments Normal, n (%) Mild DD or mild MR, n (%) Moderate DD or moderate MR, n (%) Severe DD or severe MR, n (%) Profound MR, n (%)
33 33 32 28 28 24 20
(89.2) (89.2) (86.5) (75.7) (75.7) (64.9) (54.1)
14 (37.8) 37 (100) 37 (100) 25 (67.6) 19 (51.4) 1 15a 2 1b 13 (35.1) 12 (32.4) 2 (5.4) 3 (8.1) 1 (2.7)
4 (10.8) 7 (18.9) 16 (43.2) 10 (27.0) 10 (27.0) 2 (5.4) 8 (21.6) 9 (24.3) 12 (32.4) 6 (16.2)
DD, developmental delay; DTP vaccine, Diphtheria, Tetanus, and Pertussis vaccine; GCs, generalized clonic seizures; GTCs, generalized tonic-clonic seizures; JE vaccine, Japanese encephalitis vaccine; mo, months; MR, mental retardation; n, numbers. a Two cases 19 and 25 exhibited seizures while receiving the third dose of DTP vaccine at 6 months of age and the first dose of JE vaccine at 15 months of age. b Case 29 manifested seizures while receiving rotavirus vaccine at 4 months of age and pneumococcus vaccine at 14 months of age. c Traditional antiepileptic drugs include Clobazam, Clonazepam, Levetiracetam, Sodium valproate, or Topiramate.
there were no reported SNPs related to the novel mutations in our study. We also used two tools of polymorphism phenotyping v2 (PolyPhen-2) and sorting intolerant from tolerant (SIFT) to analyze these
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Table 2 SCN1A gene mutations of 37 patients with Dravet syndrome. SCN1A Case
Type of mutation
Exon
Amino acid changea
Location in protein
Novel mutation [ref]
34 9 13 8 20 27 1 5 31 35 26 36 16 21 7 33 22 17 2 12 15 32 30 37 4 11 10 14 28 25 23 6 3 19 24 29 18
Nonsense mutation Nonsense mutation Nonsense mutation Nonsense mutation Nonsense mutation Nonsense mutation Nonsense mutation Nonsense mutation Nonsense mutation Frameshift mutation Frameshift mutation Frameshift mutation Frameshift mutation Frameshift mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Missense mutation Splice mutation Splice mutation Splice mutation Splice mutation Splice mutation
1 5 5 11 11 11 12 12 15 2 6 6 25 26 2 2 5 5 5 9 9 15 20 20 21 21 22 22 23 25 26 26 Intron Intron Intron Intron Intron
R19X R222X R222X R613X R542X R542X Q711X R712X R862X I91fs I264fs D313fs S1615fs K1846fs R101Q L93S D194A K225N Y317H R393C S243F R946C R1322I K1313I C1354Y V1390M K1432R A1441T Q1450P V1612I R1642M I1683T IVS 1 +G > C IVS 4 +1G > A IVS 15 –4 12 del IVS 21-1 G > A IVS 24+5 G > C
N-terminal D1S4 D1S4 L1 L1 L1 L1 L1 D2S4 N-terminal D1S5 D1/S5–S6 D4S3 C-terminal N-terminal N-terminal D1S3 D1S4 D1/S5–S6 D1/S5–S6 D1S6 D2/S5–S6 D3S4 D3S4 D3S5 D3/S5–S6 D3/S5–S6 D3/S5–S6 D3/S5–S6 D4S3 D4S4 D4S5 N-terminal D1S2 D2S6 D3/S4–S5 L3
Yes No [18] No [18] No [18] No [18] No [18] Yes No [18] No [19] Yes Yes Yes Yes No [18] No [18] Yes Yes Yes Yes No [18] Yes No [18] Yes Yes Yes No [20] Yes Yes Yes No [21] Yes No [18] Yes No [22] Yes Yes Yes
1 4 15 21 24
The neuronal voltage-gated sodium-channel a-subunit (SCN1A) is organized in four homologous domains (D1–D4), each of which contain six transmembrane a helices (S1–S6) and an additional pore loop (L) located between the S5 and S6 segments, plus a carboxy terminus (C-terminal), and a amino terminus (N-terminal). [ref], [reference]. a Protein sequence of SCN1A was based on ENSEMBL ENST00000423058.
and wave discharges. Focal spikes were located on the frontal and temporal areas with frontal predominance. 4. Discussion The first interictal awake EEG recordings in SCN1Apositive DS showed that 86.4% of patients exhibited nonspecific features and 13.5% had epileptiform discharges at the median age of 1 year and 11 months. None of our cases exhibited electric photosensitivity despite the fact that clinical photosensitivity was 35.1%. Both of these observations were in contrast to previous studies that reported epileptiform abnormalities in the progression of EEG features became evident in 59–77% of DS patients during the second year of life
[24], and generalized photoparoxysmal responses (PPR) during IPS were reported in at least 40% of DS cases which would reinforce the diagnosis [24–26]. Our observation of a low rate of interictal epileptiform discharges and no elicitation of PPR during IPS might be for some limitations. The first one was that our patients were present to our hospitals at various first-visit ages with a range of 5 months to 7 years and 4 months, and some patients received medications before, both of which might influence the results of the interictal EEG recordings at the time of examinations. The second was our first interictal EEG studies were only recorded in the awake stage for the following HWBT, and the results of EEG findings could be more informative if sleep EEG recordings were performed. The third was that a
Case
604
Table 3 EEG findings of patients with SCN1A-positive Dravet syndrome. Age
Age at Sz onset
The first EEG recording Age
Interictal EEG
Ictal EEG
Simultaneous ictal seizure patterns
Duration
1
F
25y 3mo
6mo
3y
Gen. spikes ! MCA
MS ! AAS ! GTCS
1 min 35 s
2
F
12y 3mo
10mo
2y 1mo
11 min
M M
8y 7mo 13y 11mo
2mo 6mo
8mo 7y 4mo
Gen. spikes ! polymorphic background slowing Gen. 2–3 Hz high voltage slow waves Gen. spikes ! MCA
MS ! GCS ! CPS
3 4
MS, migrating MS ! GTCS
8 min 1 min 2 s
5
M
7y
3mo
7mo
Background slow Background slow Normal Background slow Normal
MS ! focal Sz ! GTCS ! CPS
4 min 46 s
6 7
F M
8y 11mo 5y 7mo
2mo 6mo
3y 2mo 2y 2mo
MS ! focal Sz ! GTCS ! GCS ! CPS MS ! focal Sz ! GCS
1 min 14 s 1 min
8 9 10 11 12
F F F M M
3y 8mo 6y 2mo 5y 8mo 2y 9mo 12y 9mo
6mo 9mo 6mo 4mo 2mo
1y 3mo 3y 9mo 3y 4mo 8mo 2y 9mo
MS ! focal Sz ! GTCS MS ! CPS ! focal Sz ! GTCS MS ! focal Sz ! GTCS MS ! SPS and MS AAS ! MS ! focal Sz ! GCS ! CPS
2 min 16 s 2 min 2 min 28 min 23 s 1 min 57 s
13
M
10y 10mo
7mo
1y 3mo
AAS ! MS ! focal Sz ! MS ! CPS
51 s
14
F
14y 5mo
4mo
5y 10mo
Gen. 2–2.5 Hz SWD ! MCA Gen. 3–3.5 Hz SWD ! Gen. spikes ! MCA Gen. spikes ! MCA Gen. spikes ! focal spikes and polyspikes Gen. spikes ! MCA ! Gen.3–4 Hz SWD and spikes Focal spikes ! Gen. spikes ! focal spikes ! Gen. spikes Focal spikes ! GED ! MCA
AAS ! focal Sz ! GTCS
1 min 9 s
15
F
7y 11mo
6mo
11mo
Focal spikes ! GED
AAS ! MS ! CPS ! focal Sz ! CPS
2 min 16 s
16
M
6y 2mo
6mo
1y 1mo
AAS ! CPS ! MS
2 min 30 s
17
M
8y 9mo
6mo
4y
Focal spikes ! Gen. 2.5–3 Hz SWD ! focal spikes GED ! MCA
AAS ! GCS ! focal Sz
2 min 34 s
18 19
F F
11y 1mo 7y
5mo 2mo
6y 6mo 2y 10mo
AAS ! CPS AAS ! focal Sz ! GCS ! MS, migrating
2 min 3 min 30 s
20
F
10y 3mo
7mo
1y 9mo
Focal spikes ! Gen. spikes ! focal spikes Focal spikes ! Gen. 3–3.5 Hz SWD ! MCA ! Gen. spikes MCA ! Gen. spikes
GCS ! focal Sz ! MS
1 min 58 s
21 22
M M
13y 2mo 23y 9mo
2mo 4mo
8mo 6y 3mo
MCA MCA
GTCS GTCS
33 min 2 min 20 s
23 24
M M
17y 5mo 10y 11mo
6mo 8mo
1y 4mo 2y 1mo
MCA MCA ! Gen. 2–3 Hz SWD ! Gen. spikes
GTCS Focal Sz ! GTCS ! MS ! Focal Sz
36 min 5 min 22 s
25
F
8y 8mo
6mo
9mo
Focal sharp waves ! Gen. 4–5 Hz SWD ! focal spikes
Focal Sz ! CPS ! MS ! CPS ! GTCS
2 min 24 s
Excess fast Background slow Normal Gen. spikes Normal Normal Background slow Gen. spikes Focal/Gen. spikes Background slow Normal Background slow Focal spikes Background slow Background slow Normal Background slow Normal Background slow Focal sharp waves
Gen. 2.5–3 Hz SWD ! Gen. 1–2 Hz SWD ! MCA Focal spikes ! GED ! MCA Focal spikes ! GED
H.-F. Lee et al. / Brain & Development 37 (2015) 599–611
Gender
Gen. 3–3.5 Hz SWD ! focal spikes ! Gen. spikes ! GED Not detected
CPS ! AAS ! focal Sz ! GTCS
10 min 17 s
Not detected
Not detected
Not detected
10mo
Background slow Normal
Not detected
Not detected
3mo
3y 3mo
Excess fast
Not detected
Not detected
18y 1mo
11mo
11mo
Normal
Not done
Not available
F
26y 4mo
5mo
5mo
Normal
Not done
Not available
33
M
25y 2mo
9mo
9mo
Normal
Not done
Not available
34
M
26y 5mo
6mo
11mo
Not done
Not available
35
F
16y 7mo
5mo
5mo
Background slow Normal
Not done
Not available
36
F
15y 8mo
6mo
6mo
Normal
Not done
Not available
37
F
5y
8mo
3y 8mo
Normal
Not done
Not available
Not available Not available Not available Not available Not available Not available Not available Not available Not available Not available Not available
M
13y 11mo
5mo
5y 2mo
27
M
13y 8mo
5mo
3y 7mo
28
M
11y 10mo
8mo
1y 11mo
29
M
6y 7mo
4mo
30
M
7y 9mo
31
M
32
AAS, atypical absence seizure; CPS, complex partial seizure; F, female; GCS, generalized clonic seizure; GED, generalized epileptiform discharges; Gen., generalized; GTCS, generalized tonic-clonic seizure; MCA, muscle contraction artifact; mo, months; MS, myoclonic seizures; SPS, simple partial seizure; SWD, spike and wave discharges; Sz, seizure; y, years.
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Background slow Normal
26
605
606
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Fig. 1. Pleomorphic ictal electroencephalographic seizure patterns of case 19, aged 2 years and 10 months. (A) Before the hot water bath test (HWBT), the interictal EEG shows slowing background activity. (B) 14 min and 15 s after starting the HWBT, she exhibits clinical features of intermittent eye staring and dreaming. Initial duration of each episode is one to two seconds followed by longer durations intermittently, with longest duration of 10 s. The EEG recording shows focal spikes arising from the right hemisphere followed by generalized 3–3.5 Hz spike and wave discharges. (C) Sudden motionless, eye staring, yelling, eye deviation to the left side followed by generalized clonic seizures and lip cyanosis develop, lasting around 30 s. The simultaneous body and water temperatures are 37.8 and 39 °C, respectively. The EEG recording reveals muscle contraction artifact. (D–E) Evolution into migrating myoclonus occurs later on. The EEG recording shows generalized spike and wave discharges, and the density of epileptiform discharges decrease as the frequency and intensity of myoclonus lessen. The total duration is 70 s. (F) Post-ictal phase is characterized by eye opening and lying motionless, and the EEG trace shows a flat background activity. (G) Post-ictal phase reveals sleepiness, and the EEG trace shows slowing background activity.
discrepancy between laboratory EEGs’ photosensitivity and everyday clinical sensitivity to light has been reported to occur in DS patients [30]. Taken together, the interictal awake EEG features in our case series revealed that the majority of cases had normal results, slowing background activities or fast waves, and there was a low detection rate of abnormal epileptiform discharges and PPR at IPS. We suggest that normal and/ or nonspecific interictal awake EEG features are indicative of limit value. The accurate diagnosis of DS remains fundamentally reliant on clinical characteristics of seizure type and genetic analyses [31,32]. Ictal electroencephalographic recordings induced by HWBT were very different and polymorphous. We observed that the median number of evolutionary seizure types was three. Regarding the first recognized seizure type, the most common seizure semiology was myoclonic seizure. Myoclonic seizures in DS have been reported to be heterogeneous and include epileptic or nonepileptic myoclonus [26]. The concomitant EEG findings of myoclonic seizures could show generalized
or multiple spike and wave discharges, at 3 Hz or more [26], which were similar to our results of generalized or focal spikes, generalized 2–3.5 Hz spike and wave discharges or generalized 2–3 Hz high voltage slow waves. The most common seizure type following initiation of myoclonic seizure was unilateral focal motor seizure in 5 of the 11 patients. An exception was case 3, who presented with migrating myoclonic seizures as his sole clinical seizure type during the course of recording. The second most common first-recognized ictal seizure type was atypical absence seizure. Atypical absence seizures have been proposed to be classified into atypical absence seizures with impaired consciousness only and those with myoclonic component [26]. In both seizure types, the EEG recording might show generalized irregular spikes and waves at 2–3.5 Hz, and the myoclonic seizures might be very mild and isolated during the spike and wave bursts [26]. Our case series also showed that 5 of 8 patients who presented with atypical absence seizures as their first ictal seizure type exhibited myoclonic seizures either as the coming seizure type or as one of
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Fig. 1 (continued)
607
608
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Fig. 1 (continued)
multiple evolutionary seizure patterns. Case 19 demonstrated atypical absence seizure and myoclonic seizure occurred separately between polymorphic seizure types.
A previous report showed that unilateral motor seizures were usually long-lasting in DS and might constitute an epileptic status [31]. Our study revealed one patient, case
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609
Fig. 1 (continued)
11, with seizure duration longer than 15 min actually exhibited myoclonic seizures preceded by simple partial motor seizures, which are rarely described in the
literature [24,26]. Tonic seizure was not identified in our case series, which was consistent with results reported in the literature [26]. We conclude that the ictal
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electroencephalographic findings during HWBT in patients with SCN1A-positive DS appear to be widely diverse. However, a limitation in our study was that the absence of ictal EEG findings of unprovoked habitual seizures could be comparable with those of hot water bath induced seizures. Given that both the appearance of clinical features and EEG recordings of DS are age-dependent, a definite diagnosis can usually be made based on the presence of all the symptoms and confirmation by comprehensive electroclinical studies until early childhood. Nevertheless, our study showed in a six-year follow-up of interictal awake EEG features that there were no significant changes, i.e., 86.4% of initial awake EEGs vs. 84.4% of follow-up awake EEGs showing nonspecific findings, and 13.5% of initial awake EEGs vs. 15.6% of follow-up awake EEGs revealing abnormal epileptiform discharges. We suggest that routine follow-up awake EEGs should not be repeated very often. In conclusion, the first and follow-up interictal awake EEG recordings in the majority of SCN1A-positive DS patients disclosed normal results and nonspecific findings. There was a discrepancy between the two EEG results for photosensitivity and clinical sensitivity to light. Ictal electroencephalographic seizure types and concomitant EEG recordings were diverse and polymorphous, in which myoclonic seizures and atypical absence seizures were the two most common recognized ictal seizure types. A low rate of interictal awake epileptiform abnormalities might make patient management more challenging.
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