Early myoclonic encephalopathy

Early myoclonic encephalopathy
ICD-10	G 40.3
MeSH	D004831

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ;Associate Editor(s)-in-Chief: Aditya Govindavarjhulla, M.B.B.S. [2]

Synonyms and keywords: Neonatal myoclonic encephalopathy

Overview

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.

Classification

According to International Classification of Epilepsies and Epileptic Syndromes(ILAE), early myoclonic encephalopathy is categorized as age related, generalized symptomatic epilepsy of non specific etiology. Early infantile epileptic encephalopathy has two different variants

• Early myoclonic encephalopathy
• Ohtahara syndrome

Pathophysiology

Genetics

• In most cases the disease appears to be inherited as an autosomal recessive trait.

Associated Conditions

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

Causes

Cause is uncertain.

Differentiating Early myoclonic encephalopathy from other Diseases

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

• Ohtahara syndrome
• West syndrome
• Lennox-Gastaut syndrome

Differentiating features are:

Features/Disease	Early myoclonic encephalopathy	West syndrome	Lennox-Gastaut syndrome
Age at presentation	Early infancy	Infancy	Early childhood
Diverse seizures	May or may not be present	Not present	Present
Tonic spasms	May or may not be present	Present	Not present
Response to ACTH	Poor	Good	Poor
Interictal EEG	Suppression bursts	Hypsarrhythmia	Diffuse slow spike wave

Differentiating Early myoclonic encephalopathy from Ohtahara syndrome:

Features/Disease	Early myoclonic encephalopathy	West syndrome
Etiology	Non structural or metabolic	Structural brain lesions
Clinical	Myoclonia and partial seizures	Tonic spasms
Suppression bursts(SB)	More apparent in sleep	Consistently seen in wakeful and sleep states
Course	SB's persist to childhood with transient transformation to hypsarrhythmia	Evolve to hypsarrhythmia and then to diffuse slow spike waves
Transformation	Persists for long period	Evolves to West syndrome and then to Lennox-Gastaut syndrome

Epidemiology and Demographics

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

Risk Factors

Risk factors include

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

Screening

• There is no screening procedure as such for early moclonic encephalopathy.
• Every child with a presentation of seizure (partial or complete) must undergo EEG evaluation.

Natural History, Complications, and Prognosis

Natural History

Symptoms may occurs 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 at around 3-4 months of age.

Complications

• Severe neurological impairment
• Mental retardation
• Vegetative state

Prognosis

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

Diagnosis

Symptoms

• Recurrent seizures
• Developmental delay

Family History

• 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.

Birth History

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

Physical Examination

Appearance of the Patient

• Floppy due to hypotonia

Neurologic

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

Laboratory Findings

Biomarker Studies

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

CT and MRI

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

Electroencephalogram(EEG)

Characteristic features include

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

Treatment

Pharmacotherapy

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

Genetic Counseling

• It may aid in early diagnosis and prevention to certain extent.

References

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