This article includes discussion of myoclonic epilepsy in infancy, idiopathic myoclonic epilepsy in infancy, benign myoclonic epilepsy in infancy, myoclonic epilepsy in infancy and childhood, MEI, and reflex myoclonic epilepsy in infancy. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
Myoclonic epilepsy in infancy usually appears between 4 months to 3 years of age. It is characterized by the occurrence of myoclonic seizures as the unique type of seizure (expect simple febrile seizure) occurring in normal infants, either spontaneously or induced by acoustic, tactile, or more rarely, photic stimuli (reflex form), and is usually responsive to valproate monotherapy. The long-term outcome is favorable in about 80% of patients, with disappearance of seizures and normal cognitive functioning. However, reports of protracted evolution show that about 20% of patients have other seizure types, mainly at adolescence, and that about 30% have mild cognitive impairment. The author underscores the problem of terminology due to the new proposal of classification by the ILAE Task Force, in which the term “idiopathic” is replaced by “genetic.” The author also discusses the relationship between myoclonic epilepsy of infancy and other idiopathic generalized and focal epilepsies, such as juvenile myoclonic epilepsy, epilepsy with myoclonic-atonic seizures, Jeavons syndrome, and childhood epilepsy with centrotemporal spikes.
• Myoclonic epilepsy in infancy (formerly named “benign myoclonic epilepsy in infancy”) encompasses 2 forms: 1 with spontaneous seizures and 1 with reflex seizures. Spontaneous and reflex seizures may occur in the same infant.
• Myoclonic epilepsy in infancy is not actually benign in all affected children, but seizures are self-limited mainly in the reflex form and pharmacoresponsive mainly in the spontaneous form.
• In spite of complete remission of seizures, long-term cognitive outcome is abnormal in around 30% of patients, usually in the range of mild impairment and rarely severe. The factors of this unfavorable outcome remain unknown.
• Myoclonic epilepsy in infancy shares common traits with other idiopathic generalized and focal epilepsies, and its etiology seems to be genetic.
Historical note and terminology
The description of myoclonic epilepsy in infancy (formerly named “benign myoclonic epilepsy in infancy” or “idiopathic myoclonic epilepsy in infancy) has been attributed to Dravet and Bureau in 1981 (Dravet and Bureau 1981). They described “benign myoclonic epilepsy in infancy” in 7 normal children in the first 3 years of life. The syndrome was defined as including myoclonic seizures only, except rare simple febrile seizures, with good prognosis regarding response to therapy and cognitive functions. Prior to this, early benign myoclonic epilepsy was reported in 3 infants in a study of early-onset epilepsies (Dalla Bernardina et al 1978), but without known follow-up. In 1977 Jeavons gave the name ‘‘myoclonic epilepsy of childhood'' to a similar type of syndrome, beginning at 3 years of age (Jeavons 1977). Approximately another 200 cases have since been published.
The benignity of the syndrome has been questioned, leading to a change in its name to “myoclonic epilepsy in infancy” (Engel 2006; Zuberi and O'Regan 2006). “Idiopathic myoclonic epilepsy in infancy” has been proposed (Dravet and Vigevano 2008). However, the last report of the ILAE Commission on Classification and Terminology proposed replacing “idiopathic” with “genetic,” giving a narrow definition of genetic (Berg et al 2010). Therefore, idiopathic myoclonic epilepsy in infancy should be placed among the epilepsies of unknown etiology (Guerrini et al 2012). Also, because the age of onset may be after the infantile period (infancy is from 4 weeks to 1.5 years of age) to early childhood (early childhood is from 1.5 to 4 years of age), the name of “myoclonic epilepsy in infancy and early childhood” has been proposed (Covanis 2010). The ILAE Commission has recommended that the term idiopathic can be used (Scheffer et al 2017).
Some authors have described cases with reflex myoclonias triggered by unexpected auditory or tactile stimuli and have proposed to distinguish 2 separate entities, the second one being named “reflex myoclonic epilepsy in infancy” (Ricci et al 1995; Vigevano et al 1997; Verrotti et al 2013a; Verrotti et al 2013b). There is still a debate over whether there are really 2 distinctive syndromes. Few cases with photosensitive benign myoclonic epilepsy have been reported (Capovilla et al 2007). However, the ILAE epilepsy diagnosis manual does not find this distinction necessary, and all the cases are described as myoclonic epilepsy in infancy (Commission on Classification and Terminology of the International League Against Epilepsy 2017).
In the ILAE proposal, myoclonic epilepsy in infancy is classified among neonatal/infantile epileptic syndromes (Berg et al 2010). The following is a complete description from the ILAE epilepsy manual (Commission on Classification and Terminology of the International League Against Epilepsy 2017):
Overview. This epilepsy syndrome is uncommon. Myoclonic seizures are the only seizure type seen at onset, although infrequent febrile seizures may also occur. Myoclonic seizures may be activated by photic stimulation in some patients, whereas others may have myoclonic seizures that are induced by sudden noise or touch. Cognitive, behavioral, and motor difficulties may exist. Seizures are self-limiting, ceasing within 6 months to 5 years from onset. Generalized convulsive seizures may be seen in later life.
Note. Self-limiting refers to seizures having a high likelihood of spontaneously remitting at a predictable age.
Clinical context. This syndrome is characterized by the onset of myoclonic seizures between the ages of 6 months and 2 years, and in some cases, earlier (4 months) or later (2 to 4 years) onset has been reported. Myoclonic seizures may be induced by photic stimulation in some patients or by sudden noise or touch in others. Infrequent febrile seizures may be seen in approximately 10% of patients. Seizures remit within 6 months to 5 years from onset, but generalized convulsions may be seen in teenage years in 10% to 20% of patients. Patients with photosensitivity may have seizures that are more difficult to control. Males are twice as likely to be affected as females. Antecedent and birth history is unremarkable. Head size and neurologic examination are normal. Cognitive, motor, and behavioral difficulties are reported, especially if seizures are not controlled.
Mandatory seizures. Myoclonic seizures are seen. These are mainly of the head (causing nodding), eye balls (which roll upwards), upper extremities (causing the arms to fling up and out), and the diaphragm (resulting in vocalization). Rarely, the lower limbs are affected, causing falls. Jerks can be singular or can occur in a series and may vary in severity. Responsiveness is preserved; however, it may be reduced if there are clusters of jerks in a series. Jerks may occur in all states (alert, drowsiness, slow sleep, and on wakening).
Patients may have:
• Simple febrile convulsions (seen in 10%, infrequent)
Exclusionary. Other seizure types are exclusionary.
EEG Background. The background EEG is normal.
Interictal EEG. The interictal EEG is normal.
Activation. Sleep may activate the EEG, and generalized spike-and-wave and polyspike-and-wave may occur, with or without accompanying myoclonic jerks clinically. One fifth of patients have photosensitivity, with myoclonic jerks precipitated by photic stimulation. In 10% of patients, myoclonic jerks may be activated by sudden noise or touch in either awake or sleep states.
Ictal EEG. Myoclonic jerks are associated with generalized spike-and-wave or polyspike-and-wave discharges.
Imaging. Neuroimaging is normal.
Genetics. The pattern of inheritance is unknown but is likely genetic. There are no known genes.
Family history of seizures/epilepsy. A family history of febrile seizures or epilepsy is seen in one third of patients.
• Dravet syndrome: myoclonic seizures are frequent, however typically occur in the second year of life and are preceded by a period of susceptibility to febrile convulsions.
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