| Benign familial and
nonfamilial infantile seizures by Federico Vigevano Date of submission: February 28, 2003 Date of update: March 2004 Medline SEARCH DATE: March 2004 |
ACKNOWLEDGEMENTS AND DISCLOSURES Please disclose any financial or other conflicts of interest that might bias your contributions, or give rise to the perception of such bias. Relevant financial ties can include consultantships, memberships in speaker's bureaus, grants, research support, salaries, royalties, ownership, equity positions, stock options, or other financial arrangements wherein you stand to gain substantially from an increase of stock value or corporate revenues. THUMBNAILSo that MedLink Corporation can highlight your clinical summary and your authorship on the MedLink Neurology home page and in our weekly email to subscribers, we ask that you provide here a brief overview of your subject (about 50 to 100 words) aimed at enticing readers to view this clinical summary. For updates, please include a sentence that refers to something new you have added. Refer to yourself in the 3rd person (eg, Dr. Doe of Superior Institution explains the basics…). For more information and examples of thumbnails, please see the Instructions to Authors, which can be downloaded from your "My Writing Assignments" page in the Online Submission System (http://www.medlinkoss.com). Current thumbnail: HISTORICAL NOTE AND NOMENCLATURE In 1963 Fukuyama reported cases occurring in the first 2 years of life that were characterized by partial seizures, absence of etiologic factors, and benign outcome ( Fukuyama 1963). Later, other reports evidenced the localization and semiology of seizures (Watanabe et al 1987; Watanabe et al 1990; Watanabe et al 1993), prognosis (Sugiura et al 1983), and presence or absence of familial occurrence (Vigevano et al 1990; Vigevano et al 1992; Vigevano et al 1994). In particular, on several occasions, Watanabe and coworkers described partial epilepsy of infancy with complex partial seizures and benign partial epilepsy with secondarily generalized seizures in infancy. Most of these cases were not familial. Vigevano and coworkers directed their attention to cases that exhibited a family history of convulsions with benign outcome during infancy and autosomal dominant inheritance, suggesting the term "benign infantile familial convulsions.” The ILAE Task Force on Classification and terminology recently stated that the term "seizure" is preferred to the term "convulsion" (Engel 2001). Just as benign seizures with neonatal onset are distinguished in familial and nonfamilial forms, benign infantile seizures are also now divided into familial and nonfamilial forms (Engel 2001). These 2 forms may, however, have characteristics that overlap (Lispi et al 2001; Caraballo et al 2003). Genetic studies in familial forms led to the identification of a chromosome marker on chromosome 19 (Guipponi et al 1997). This was not confirmed by later studies, however, and genetic heterogeneity was hypothesized (Gennaro et al 1999). In 1997 Szepetowski described the association between benign infantile familial convulsions and variably expressed paroxysmal choreoathetosis (Szepetowski et al 1997). The identification of a specific marker on chromosome 16 constituted a variant of the familial forms, called "infantile convulsions and choreoathetosis." In 2001 Caraballo and colleagues found a linkage of pure benign infantile familial convulsions to chromosome 16 in the infantile convulsions and choreoathetosis region, suggesting that this is a major genetic locus underlying both benign infantile familial convulsions and paroxysmal choreoathetosis (Caraballo et al 2001). At the same time, Malacarne and colleagues found a novel locus on chromosome 2, confirming the genetic heterogeneity of this syndrome. Considering that convulsive manifestations are limited to a short period of time, some authors hypothesized the existence of particular etiological factors in some sporadic cases. These hypotheses appear in reports of cases of benign infantile convulsions associated with prolonged episodes of diarrhea caused by rotavirus infections (Itou et al 1988; Contino et al 1994; Imai et al 1999). A clear cause-effect relation is still to be demonstrated.
Age at onset has been reported from 3 to 20 months of age, but in the familial forms it occurs mostly between 4 and 7 months. Only McCallenbach and colleagues observed a lower age at onset ranging from 6 weeks to 10 months (McCallenbach et al 2002). Findings for all etiological investigations, especially metabolic and neuroimaging tests, are normal. History of pregnancy and delivery are unremarkable. Familial cases include relatives of first and second degree who had benign infantile convulsions without subsequent development of other forms of epilepsy. The incidence in these families of other idiopathic epilepsies and febrile convulsions does not differ from that of the general population, and there were no reports of convulsions in the neonatal period. The disorder seems to be transmitted with autosomal dominant inheritance. Greater incidence among females was reported for familial forms, but this prevalence was not confirmed among the relatives (Vigevano et al 1992). All children had absolutely normal psychomotor development before the onset of seizures. An almost constant characteristic is the occurrence of seizures in a cluster: mostly brief and successive seizures, maximum of 8 to 10 daily, that did not reach a true status epilepticus. Interictal clinical condition was normal, with occasional sopor that could be attributed mostly to drug treatments. Isolated seizures in the 10 to 15 days before the cluster were reported in about one third of the cases. Seizures were usually longer in the beginning, lasting 2 to 5 minutes, and became shorter as treatment took effect. The cluster could last 1 to 3 days. As concerns the semiology of the seizures, it is difficult to say if there are real differences between the sporadic and familial forms. Elements common to both forms include motor arrest, impairment of consciousness, staring, and convulsive movements. Watanabe stressed the presence of limb or oral and facial automatisms in cases described as benign partial epilepsy with complex partial seizures (Watanabe et al 1990), and of prompt generalization with tonic-clonic manifestations in cases described as benign partial epilepsy with secondarily generalized seizures (Watanabe et al 1993). On the other hand, in addition to the symptoms already described, Vigevano documented the presence during seizures of slow deviation of head and eyes to 1 side, diffuse hypertonia, cyanosis, and unilateral limb jerks that begin unilaterally and are synchronous or asynchronous (Vigevano et al 1992). The side of the head and eye deviation sometimes changed from seizure to seizure in the same patient. When described, interictal EEG before and after the cluster is normal. Vigevano reported lateralized slow waves and spikes in the occipitoparietal areas in the interictal EEG performed during a cluster of seizures. In the presence of secondary generalization, ictal EEG disclosed a focal discharge characterized by recruiting rhythm of increasing amplitude spreading over the hemisphere and involving the entire brain. The alternating clinical pattern described by Vigevano is confirmed by recordings in the same patient of seizures with onset occurring sometimes on the right hemisphere, sometimes on the left. The site of origin of the seizures seems to be a distinguishing characteristic. According to Watanabe, the site of origin in the cases described as benign partial epilepsy with complex partial seizures (Watanabe et al 1990) is the temporal area, whereas the site varies in cases described as benign partial epilepsy with secondarily generalized seizures (Watanabe et al 1993). In familial cases, the seizures originate in the parieto-occipital area, with the side varying from 1 seizure to another (Vigevano et al 1992). In 2001, while comparing cases with familial and nonfamilial benign infantile seizures, Lispi and colleagues found that the site of origin is not a statistically significant distinction between the 2 groups. Caraballo and colleagues, studying 25 cases with benign familial infantile seizures and 39 cases with benign non familial infantile seizures, found no electroclinical differences between the 2 groups (Caraballo et al 2003). Generally, no further seizures are observed in cases treated pharmacologically. In untreated cases, there can be isolated or brief clusters within 1 year of age. In cases associated with paroxysmal choreoathetosis, the clinical picture of infantile seizures is the same as that already described. Choreoathetotic movements start during infancy or childhood, are of dystonic type, occur at rest, or can be induced by exertion or anxiety (Szepetowski et al 1997).
We present an example of a familial case reported also by Giordano and colleagues (Giordano et al 1999). A female patient, aged 3 months 21 days, was referred because she presented a cluster of seizures characterized by fixed eyes, bilateral clonic jerks, and loss of consciousness that lasted 2 minutes. On admission, a seizure demonstrating slow deviation of the head and eyes both to the left and right, loss of consciousness, oral automatisms, diffuse hypertonia, and bilateral clonic jerks was observed. All laboratory (organic acids, lactate, pyruvate, ammonia in plasma, and urine) and neuroradiological (CT and MRI) findings were negative. Both awake and sleep EEGs were normal. At that time, neurologic examination and psychomotor development were normal, and no antiepileptic drug therapy was prescribed by parent’s choice. Subsequently, the patient presented 3 or 4 seizures every month from ages 5 to 7 months. Only 1 seizure was reported from ages 7 to 11 months. The patient has been seizure-free since age 1 year. Neurologic examinations and developmental milestones have always been normal. Eighteen of 35 members of the mother’s family had benign convulsions during infancy. In particular, the father and all, except 1, of the mother’s siblings (4 sisters and 6 brothers) presented similar seizures. In all 18 members of the affected family, the clinical characteristics of the seizures were similar to those described in the proband. In all 18 members, seizure onset began at 3 to 4 months of age and ceased between ages 9 and 10 months. All presented episodes in cluster at onset and subsequently isolated seizures, with frequency similar to that of the proband. As decided by the proband’s grandmother, who always considered this type of convulsion to be a characteristic trait of the family, none of the 18 subjects received antiepileptic drug treatment. All 18 subjects had normal psychomotor development and attended high school. None of them presented febrile convulsions, nor did they develop epilepsy.
Autosomal dominant transmission is evident in the familial cases. Because of the strong similarity to benign neonatal familial convulsions, researchers at first tried to find the chromosome markers described in this syndrome (Leppert et al 1989; Ryan et al 1991). In 1994 Malafosse demonstrated that benign infantile familial convulsions is not an allelic form of benign neonatal familial convulsions, excluding the marker on chromosome 20 (Malafosse et al 1994). In 1997 linkage analysis was carried out in 5 Italian benign infantile familial convulsions families, and a locus was mapped on chromosome 19q12-13.1 between markers D19S49 and D19245 (Guipponi et al 1997). Later, in a linkage analysis on 7 families of Italian origin, Gennaro and coworkers demonstrated the presence of linkage to chromosome 19q in a single family, suggesting genetic heterogeneity within the families examined (Gennaro et al 1999). The studies on familial cases with infantile convulsions and choreoathetosis are especially interesting. In 1997 Szepetowski demonstrated linkage to the pericentromeric region of chromosome 16 in 4 French families with this syndrome (Szepetowski et al 1997). This finding was later confirmed by Lee and coworkers (Lee et al 1998) in a family of Chinese origin. In 2001 Caraballo and colleagues found linkage on chromosome 16p12-q12, the same region as infantile convulsions and choreoathetosis, in 7 families with only benign familial infantile seizures. Considering that a previous report described a large family affected by paroxysmal kinesigenic dyskinesia without infantile convulsion, with linkage to the infantile convulsions and choreoathetosis region (Bennett et al 2000), Caraballo hypothesized that chromosome 16p12-q12 is a major genetic locus underlying both benign familial infantile seizures and paroxysmal dyskinesias. At approximately the same time, while studying 8 Italian families with benign familial infantile seizures, Malacarne and colleagues (Malacarne et al 2001) mapped a novel locus to chromosome 2q24, thus demonstrating a genetic heterogeneity as in other autosomal dominant idiopathic epilepsies.
Sporadic and familial benign idiopathic seizures may appear in the neonatal period (Plouin 1985; Miles and Holmes 1990); similarly, sporadic and familial idiopathic seizures may appear in the first year of life, especially around the sixth month. There are many clinical similarities between the 2 forms, since they are both seizures in clusters limited to a short period of life with benign outcome and autosomal dominant inheritance. A possible association with late onset motor manifestation (Dedek et al 2001) has been reported also for benign neonatal familial convulsions. In 1988 2 genetic mutations, KCNQ2 and KCNQ3 respectively, were identified in this form (Charlier et al 1998; Singh et al 1998), both associated with potassium channels. For this reason, benign neonatal familial seizures are currently considered potassium channelopathies. By analogy, we can hypothesize that benign familial infantile seizures are also channelopathies. As support for this hypothesis, it must be remembered that in 2002 Heron and colleagues reported the presence of a mutation in the sodium-channel subun gene SCN2A in 2 families with seizure onset between 1 and 3 months of life and, therefore, intermediate between neonatal and infantile forms. The authors coined the term "benign familial neonatal-infantile seizures" for their cases; however, at the present time it is difficult to sustain the existence of a third clinical form. The familial forms are dominant. Definitive identification of the genetic marker will probably be possible in the near future. It can be hypothesized that epileptic seizures are particularly likely to appear during this period of life. It should not be forgotten that other forms of cryptogenic or symptomatic epilepsy, especially infantile spasms, also appear during this period, which could explain why subjects with a specific genetic predisposition have seizures in this period of life. With the exclusion of any etiological or favoring factor in the sporadic cases as well as the symptomatic nature of these seizures, we must theorize about the existence of a genetic predisposition to convulsions, even if aspecific. We cannot even exclude the possibility that the sporadic cases are actually identical to the familial ones, only with less expressivity.
Later, both forms were reported in many different parts of the world (Lee et al 1993; Luovigsson et al 1993; Echenne et al 1994; Capovilla et al 1998; McCallenbach et al 2002). At present, we are not aware of any reliable epidemiological study on the incidence of these forms of epilepsy.
PREVENTION The diagnosis of benign infantile epilepsy with partial seizures is still difficult (Okumura et al 2000). Early diagnosis is possible only in the familial forms. In the sporadic forms with either complex partial or secondarily generalized seizures, diagnosis can be suspected in consideration of the criteria presented above, with exclusion of any possible etiologic factor. As mentioned previously, the cases described that were associated with prolonged episodes of diarrhea have clinical and EEG characteristics that coincide with those described in benign infantile seizures. The etiological role of the viral infection that caused the diarrhea has not been demonstrated. A facilitating role cannot be excluded. It is obvious that in sporadic cases, hypothetical diagnosis can be confirmed only with the demonstration of benign outcome. Some features of benign infantile familial convulsions coincide with the category of benign neonatal familial convulsions. Differential diagnosis is based on age at onset of seizures and genetic studies, and it is limited to the first 3 months of life. A recent report by Heron and colleagues, though, challenges this distinction (Heron et al 2002). In the first year of life, familial convulsions may be caused by pyridoxine dependency or deficiency (Bankier et al 1983). However, in this disorder, convulsions resistant to treatment appear in the first days of life and the clinical condition is always severe. As mentioned before, reported cases associated with choreoathetosis and genetic marker on chromosome 16 have been considered a variant of benign infantile familial convulsions. On the basis of genetic studies, it is possible to hypothesize that a single genetic variant can be the cause of both defects (Caraballo 2001). Lastly, Capovilla and Beccaria recently described 12 nonfamilial cases with benign partial epilepsy with onset in infancy and early childhood with vertex spikes and waves during sleep on EEG (Capovilla and Beccaria 2000). This form differs from benign infantile convulsions because of later onset (13 to 30 months), less frequent seizures rarely in clusters, lack of ictal automatisms, and presence of peculiar interictal EEG anomalies.
In familial cases the decision to withhold treatment can be made more easily. However, there are reports in the literature of equally effective treatment with carbamazepine, phenobarbital, valproate, or zonisamide for periods varying from 1 to 5 years. Recently, Yanagihara and colleagues reported good efficacy of low dose carbamazepine therapy (Yanagihara et al 2003).
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ILAE ICD CODE MAJOR KEYWORD DESCRIPTORS MINOR KEYWORD DESCRIPTORS AGE OF PRESENTATION AGE OF TYPICAL PRESENTATION POPULATION GROUP(S) PREFERENTIALLY AFFECTED OCCUPATION GROUP(S) PREFERENTIALLY AFFECTED SEX FAMILY HISTORY HEREDITY PERMUTED TOPIC, SYNONYMS, VARIANTS RELATED TOPICS DIFFERENTIAL DIAGNOSIS
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