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Myoclonic epilepsy with ragged-red fibers without increased lactate levels

Shigemi Kimura1, Shiro Ozasa, Kyoko Nakamura

  • 1Department of Child Development, Kumamoto University School of Medicine, Kumamoto, Japan. kimusige@kumamoto-u.ac.jp

Pediatric Neurology
|June 13, 2009
PubMed

Insights

Myoclonic epilepsy with ragged-red fibers, a mitochondrial disorder, can occur without elevated lactate levels. Suspect this condition in patients with difficult-to-control epilepsy and other mitochondrial symptoms even with normal lactate.

Area of Science:

  • Mitochondrial Medicine
  • Neurogenetics
  • Epileptology

Background:

  • Myoclonic epilepsy with ragged-red fibers (MERRF) is a mitochondrial encephalomyopathy.
  • Typically associated with mitochondrial DNA mutations (e.g., tRNA(Lys) at 8344 and 8356).
  • Key diagnostic features include myoclonic epilepsy, lactic acidosis, and ragged-red fibers.

Observation:

  • A case of MERRF presented with myoclonic epilepsy and ragged-red fibers.
  • Crucially, this patient exhibited normal lactate levels, deviating from the typical presentation.
  • Epilepsy was refractory to standard antiepileptic drug treatment.

Findings:

  • Identified pathogenic mitochondrial DNA mutations in tRNA(Lys) at positions 8344 and 8356.
  • Demonstrated that elevated lactate levels are not a mandatory diagnostic criterion for MERRF.
  • Highlighted the presence of other mitochondrial disease symptoms, including mental retardation.

Implications:

  • Broadens the diagnostic criteria for MERRF, emphasizing clinical suspicion beyond lactate levels.
  • Suggests MERRF should be considered in epilepsy cases refractory to treatment, even with normal lactate.
  • Underscores the importance of evaluating for mitochondrial disorders in patients with unexplained neurological symptoms.

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