Early myoclonic encephalopathy

Early myoclonic encephalopathy is a seizure disorder that occurs in the neonatal period. This disorder presents with features such as partial or fragmentary erratic myoclonic seizures, massive myoclonus, partial motor seizures (jerking movements of one side), and tonic seizures.

According to the International Classification of Epilepsies and Epileptic Syndromes, early myoclonic encephalopathy can be categorized as age related, and as generalized symptomatic epilepsy of a non specific etiology.^[1]

The two variants of early infantile epileptic encephalopathy are:

• Early myoclonic encephalopathy
• Ohtahara syndrome

• In most cases, the disease appears to be inherited in an autosomal recessive fashion.

• Non-ketotic hyperglycinemia
• D-glycemic acidemia
• Methylmalonic acidemia
• Propionic acidemia
• Hyperammonemia due to carbamyl phosphate synthetase deficiency

The cause of early myoclonic encephalopathy is unknown.

Early myoclonic encephalopathy has to be differentiated from a few other epilepsy syndromes due to similar presentation.

These similar epileptic syndromes include:

• Ohtahara syndrome
• West syndrome
• Lennox-Gastaut syndrome

Differentiating features are:

Differentiating Early myoclonic encephalopathy from Ohtahara syndrome:^[3]

Early myoclonic encephalopathy (EME) is a rare disease with only around 30 cases described so far.

Risk factors include:

• Structural brain lesion
• Metabolic disturbances
• Small for gestational age
• Sepsis
• Bleeding into brain(cerebral hemorrhage)

• There is no screening procedure set forth for detecting early myoclonic encephalopathy.
• Every child with a presentation of seizure (partial or complete) must undergo an EEG evaluation.

Symptoms may occur as early as a few hours after birth, and postnatal movements are sometimes reported by the mother to be of the same type as those felt at the end of pregnancy. Other types of seizures, including partial seizures, massive myoclonia, and tonic spasms can also occur; usually around 3-4 months of age.

• Severe neurological impairment
• Mental retardation
• Vegetative state

The prognosis for early myoclonic encephalopathy is poor. Children survive in a persistent vegetative state or die within the first or second year of life.

• Recurrent seizures
• Developmental delay

• There is a high risk of familial recurrence since in most cases the disease appears to be inherited as an autosomal recessive trait.
• Consanguineous marriage of parents.

• History of complicated birth may be noticed
• Post natal erratic movements
• Poor sucking and swallowing

• Floppy due to hypotonia

• Erratic myoclonus of face or extremities
• Seizures
• Severe developmental delay
• Altered mental status

• Acidosis may be noticed if any metabolic derangements coexist.
• Biochemical tests of calcium, magnesium and glucose are needed to evaluate the cause of seizures.
• High glycine levels may be detected if associated with Non-ketotic hyperglycinemia

• Identifying any structural brain lesions (malformations, tumors, bleeds)

Characteristic features on the EEG include:

• Suppression bursts
  • More apparent during sleep
• Repetitive EEG recordings are necessary for the diagnosis of early myoclonic encephalopathy.^[4]

• There are no clear guidelines for the treatment of seizures.
• Conventional drugs like valproate , clobazam , and lamotrigine are ineffective.
• Alternative therapies like ACTH, a ketogenic diet, and zonisamide are beneficial for the treatment of Ohtahara syndrome
• In patients with Non-ketotic hyperglycinemia, oral administration of ketamine, tryptophan, and dextromethorphan in combination with benzoate have brought partial improvement in symptoms and EEG findings.

• Genetic counseling may aid in the early diagnosis and prevention of EME to certain extent.

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