Benign myoclonic epilepsy in infancy (BMEI), first described by Dravet and Bureau in 1981, is a rare epilepsy syndrome.¹ It is classified among the idiopathic generalized epilepsies and typically begins by the age of 3 years.² BMEI is characterized by brief myoclonic seizures without other seizure types in developmentally normal children. The myoclonic seizures may occur spontaneously or be provoked by contact or noise. A history of simple febrile seizures may be present. In a series of 88 patients with BMEI, 26.1% had a history of simple febrile seizures.³ There is a family history of epilepsy or febrile seizures in 50% or more of patients. Myoclonic seizures are easily controlled with medication and usually remit later in childhood. Generalized tonic–clonic seizures may occur in late childhood or adolescence. Neurodevelopmental outcome is variable; most children have normal development but may experience educational difficulties.

The most common age of onset of BMEI is between 4 months and 3 years of age, but later onset up to 4 years 8 months has been reported.^4,5 The myoclonic seizures are brief, and typically involve the upper limbs and head, and less frequently the lower limbs. Seizures may be extremely subtle or may be characterized by head nodding or spasm-like events. The frequency of myoclonic seizures gradually increases over time. Studies using video-EEG recordings have demonstrated that the myoclonic jerks involve the axis of the body and the arms, provoking a head drop, and commonly result in an upward and outward movement of the upper limbs with flexion of the lower limbs. As a consequence, the patient may drop objects from the hand during the seizures or there may be a loss of posture. However, it is uncommon for the child to fall to the ground unless the lower limbs are involved. In some instances, there may be involvement of the eyeball resulting in eye rolling. Seizures typically last 1–3 seconds but are always shorter than 10 seconds. They occur multiple times daily and their onset is unpredictable. In contrast to infantile spasms, they do not occur in clusters. They tend to occur most frequently during periods of drowsiness and may be triggered by intermittent photic stimulation or a sudden noise.

Reflex myoclonic seizures, triggered particularly by noise or touch, may represent a separate clinical entity, which has been called reflex myoclonic epilepsy.^6,7,8 There is, however, controversy as to whether reflex myoclonic epilepsy in infants should be characterized separately or as part of BMEI. Capovilla and colleagues described eight children with photosensitive benign myoclonic epilepsy of infancy and proposed that this was a subgroup of children with benign myoclonic epilepsy of infancy in whom, myoclonic seizures were always triggered by photic stimulation.⁹ However, it is likely, that reflex myoclonic epilepsy is not a separate entity.

The interictal EEG background is typically normal in waking, drowsy, and sleeps states. Paroxysmal slowing, however, has been reported rarely over the central areas. Generalized spike-wave or polyspike-wave discharges may occur in drowsiness or sleep (Fig. 13–1) and these may be precipitated by intermittent photic stimulation in 20% of cases (Fig. 13–2). The ictal correlate of the myoclonic seizure is a generalized spike-wave discharge, or polyspike-wave discharges or occasionally a central spike-wave discharge (Fig. 13–3).

Limited epidemiological data are available. BMEI is rare and thought to represent less than 1% of all epilepsies and 2% or less of all genetic generalized epilepsies. There is a slight predominance in males. No familial cases have been described. However, a family history of epilepsy or febrile seizures is present in 50% of patients.³ A family history of epilepsy was reported in 27% of patients in this series, most commonly idiopathic epilepsy. In one case, the proband’s brother had the electroclinical features of myoclonic–astatic epilepsy.¹⁰

The differential diagnosis is summarized in Table 13–1.

SHUDDERING SPELLS

Shuddering spells are benign events that occur in children during the first year of life. They occur in the waking state when the infant is excited and usually involve tremulous movements of the body. The infants are normal on neurological examination and their development is normal. The EEG shows no abnormality during the events. This condition may be associated with a family history of essential tremor.

BENIGN MYOCLONUS OF INFANCY

Benign myoclonus of infancy is a nonepileptic phenomenon that occurs in normal children and is characterized by spasms that resemble infantile spasms but are not associated with an EEG abnormality.¹¹