MYOCLONUS EPILEPSY AND RAGGED-RED FIBRES (MERRF)
 
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MYOCLONUS EPILEPSY AND RAGGED-RED FIBRES (MERRF)

 

DEFINITION:

A neurodegenerative disorder characterized by myoclonic seizures, tonic-clonic seizures, and progressive neurologic dysfunction (ataxia and dementia).

EPIDEMIOLOGY:

  • incidence: rare
  • age of onset:
    • 2nd to 4th decade
  • risk factors:
    • familial
      • maternally transmitted mitochondrial DNA
      • 100% recurrence rate if mother affected
    • M = F

PATHOGENESIS:

1. Background

  • one of the 5 major conditions that account for the majority of cases of "Progressive Myoclonus Epilepsies"
  • may be a metabolic disorder involving mitochondria and represents one of the clinical phenotypes of mitochondrial encephalomyopathies
  • the presence of "Ragged-Red" fibres on skeletal muscle biopsy helps to confirm the diagnosis

2. Genetic Defect

  • genetic defect -> mitochondrial dysfunction

CLINICAL FEATURES:

1. Neurological Manifestations

1. Myoclonic Seizures

  • usually presenting symptom

2. Tonic-Clonic Seizures

  • generalized

3. Progressive Neurologic Dysfunction

  • 1. Cerebellar Ataxia
  • 2. Dementia
    • variable but progressive

    • 4. Others

    • muscular atrophy with muscle weakness
    • neuropathy
    • migraines
    • hypoventilation with sleep apnea & respiratory failure
    • sensorineuronal hearing loss
    • optic atrophy -> blindness
    • short stature
    • prognosis varies from mildly affected cases to severely affected cases with dementia, major focal neurologic defects, cortical blindness, and intractable seizures

    INVESTIGATIONS:

    1. Imaging Studies

    1. CT/MRI

    • cerebral atrophy

    2. Pathology

    1. Ragged-Red Fibres

    • diagnostic and detected by light microscopy
    • found on skeletal muscle biopsies stained with Gomori's trichrome
    • electron microscopy shows structurally-abnormal mitochondria (which are thought to produce the Ragged-Red Fibres)

    3. Electrodiagnostic

    1. EEG

    • seizure activity

    2. Evoked Potentials

    • very high amplitude visual and somatosensory evoked potentials

    4. Serum

    • elevated lactate and pyruvate

    5. CSF

    • elevated lactate

    MANAGEMENT:

    1. Supportive

    • no treatment available for this disease
    • multidisciplinary approach to ongoing problems
      • Paediatrics, Neurology, Ortho, PT, OT
      • myoclonic seizures
        • valproic acid +/- clonazepam

     

     

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