Early Myoclonic encephalopathy (EME)
Incidence
The prevalence is unknown, but the Early Myoclonic encephalopathy (EME) is a rare disease, with only about 30 cases described to date. Update 2017/ MGJM.
Clinical Characteristics
This condition is clinically characterized by the appearance of fragmentary myoclonus in the first month of life (more than half of cases have onset of seizures by 10 days of life), antecedent and birth history is typically normal, both sexes are affected equally. The seizures can be subtle myoclonic seizures, which affect small areas of the body from time to time, massive myoclonic seizures (sudden flexion or extension), focal (partial) motor seizures or, rarely, tonic spasms that affect the whole body and limbs (that cause the body and limbs to stiffen). The seizures are very frequent throughout the day. After several months the seizures may change to infantile spasms (West syndrome). Neurological examination is abnormal in keeping with the presence of severe neurological impairment. Abnormal neurological behavior may be present prior to onset of seizures. Head size is typically normal at onset; microcephaly may develop over time. Severe developmental delay is seen with or without regression. The background EEG is abnormal in all states, with a burst-suppression pattern. High voltage bursts (150-300uV) of spikes or sharp and slow waves, lasting 1-5 seconds are seen with inter-burst intervals of 3-10 seconds. The EEG may evolve to hypsarrhythmia pattern in children who evolve to have West syndrome or to a pattern of multifocal spikes and sharp waves at 3-4 months of age. Erratic myoclonus usually does not have an ictal EEG pattern but may follow bursts on the EEG. This condition should be consider in the differential diagnosis of Ohtahara syndrome. Although the etiology is unknown, at this time nonketotic hyperglycinemia, pyridoxine or pyridoxal-phosphate dependency, together with congenital deficiency of the mitochondrial glutamate transporter are known to produce a similar clinical picture, and EEG. Therefore, this condition may result from excess glutamate delivery in the synaptic cleft by the end of pregnancy.
Precipitants
None
Provocation Tests
None
Diagnostic Procedures
It is a clinical and EEG diagnosis of exclusion. If this syndrome is suspected, it is important to test the babies or infants thoroughly for a possible metabolic (biochemical) disorder, in case this in itself can be treated. They should also have detailed genetic-testing. This is to try and predict whether, if another child is born in the family, he or she may also be affected