PROGRESSIVE MYOCLONUS EPILEPSIES
 
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PROGRESSIVE MYOCLONUS EPILEPSIES

 

DEFINITION:

A group of familial neurodegenerative disorders characterized by degeneration of CNS grey matter and the clinical triad of myoclonic seizures, tonic-clonic seizures, and progressive neurologic dysfunction (ataxia and dementia).

EPIDEMIOLOGY:

  • incidence: rare
  • age of onset:
    • infancy to adulthood (depends on the Type)
  • risk factors:
    • familial - most are autosomal recessive

PATHOGENESIS:

1. Background

  • seizures in childhood can be divided into partial and generalized and the latter can be further subdivided into primary and secondary
  • Progressive Myoclonus Epilepsies (PME) represent a heterogeneous subgroup of those with secondary generalized epilepsy
  • the several diseases classified as PME have simliar clinical features:
  • 1. myoclonic seizures
  • 2. tonic-clonic seizures
  • 3. progressive neurologic dysfunction (ataxia & dementia)
  • there are 5 major and 11 rare diseases classified under PME:
  • 1. Major
  • 1. Lafora-Body Disease
  • 2. Myoclonus Epilepsy and Ragged-Red Fibres (MERRF)
  • 3. Neuronal Ceroid Lipofuscinosis
  • 4. Unverricht-Lundborg Disease
  • 5. Sialidosis
    • Galactosialidosis
  • 2. Rare
  • 1. Action Myoclonus-Renal Failure Syndrome
  • 2. Atypical Inclusion-Body Disease
  • 3. Biotin-Responsive Encephalopathy
  • 4. Dentatorubral-Pallidoluysian Atrophy
  • 5. Ekbom Syndrome
  • 6. Gaucher's Disease (noninfantile neuronopathic form)
  • 7. GM2 Gangliosidosis (late infantile, juvenile forms)
  • 8. Hallervorden-Spatz Disease
  • 9. Late-Onset Lafora-Body Disease
  • 10. May-White Syndrome
  • 11. Neuroaxonal Dystrophy (juvenile form)

CLINICAL FEATURES:

1. Neurological Manifestations

1. Myoclonic Seizures

  • sudden, brief, lightning-like jerks
  • generalized or limited to one or more muscle groups
  • no loss of consciousness
  • triggered by movement, bright light, stress

2. Tonic-clonic Seizures

  • generalized seizures

3. Progressive Neurologic Dysfunction

  • ataxia, dementia
  • PME may be difficult to diagnose initially as many patients present with only seizure activity
  • most patients develop normally until the onset of the disease whereupon there is a progressive neurological deterioration

INVESTIGATIONS:

1. Imaging Studies

1. CT/MRI

  • progressive atrophy of grey matter

2. Pathology

  • biopsy of skin (Lafora Bodies), skeletal muscle (ragged-red fibres), bone marrow (vacuolations)

3. Electrodiagnostic Tests

1. EEG

  • slowing of background rhythms with generalized epileptiform discharges and photic sensitivity

2. Evoked Potentials

  • visual, somatosensory

3. EMG & Nerve Conduction Studies

4. Serum

  • CBC, lactic acid
  • specific enzyme assays - beta-hexosaminidase A & B

5. Urine

  • screening tests - oligosaccharides, dolichol, organic acids

MANAGEMENT:

1. Supportive

  • no treatment available for most underlying diseases
  • multidisciplinary approach
    • Paediatrics, Neurology, Ortho, PT, OT

2. Seizure Control

1. Myoclonic Seizures

  • valproic acid
  • clonazepam
  • 5-hydroxytryptophan with carbidopa

2. Tonic-Clonic Seizures

  • avoid phenytoin or multiple anticonvulsants as patients with PME are prone to neurotoxic side effects

 

 

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