Respiratory chain complex-I defect mimicking myasthenia

Metab Brain Dis. 2002 Mar;17(1):41-6. doi: 10.1023/a:1014052330663.


In a 67-year-old woman with ptosis, double vision, dysphagia, ambiguous Tensilon tests, normal acetylcholine-receptor antibodies, normal thymus, and repeatedly abnormal responses to low-frequency repetitive stimulation, ocular myasthenia was suspected. Pyridostigmin was ineffective, but corticosteroids improved the abnormalities. Despite this therapy, lower-limb weakness developed. Reevaluation disclosed abnormal increase of serum lactate during slight exercise, myogenic electromyography, ragged-red fibers, reduced oxidative enzyme staining and abnormally shaped and structured mitochondria on muscle biopsy, and a respiratory chain complex-I defect on biochemical investigation of the muscle homogenate. Respiratory chain disorder due to complex-I defect with abnormal decremental response to low-frequency repetitive stimulation was diagnosed. It is concluded that respiratory chain disorders due to a complex-I defect may mimic ocular myasthenia clinically, electrophysiologically, and even therapeutically.

Publication types

  • Case Reports

MeSH terms

  • Action Potentials / drug effects
  • Action Potentials / physiology
  • Adrenal Cortex Hormones / therapeutic use
  • Aged
  • Blepharoptosis / etiology
  • Diagnosis, Differential
  • Diplopia / drug therapy
  • Diplopia / etiology
  • Electric Stimulation
  • Electromyography
  • Electron Transport / genetics*
  • Electrophysiology
  • Female
  • Humans
  • Metabolism, Inborn Errors / diagnosis*
  • Metabolism, Inborn Errors / drug therapy
  • Metabolism, Inborn Errors / genetics*
  • Muscle, Skeletal / drug effects
  • Muscle, Skeletal / physiology
  • Myasthenia Gravis / diagnosis*
  • Ophthalmoplegia / drug therapy
  • Ophthalmoplegia / etiology


  • Adrenal Cortex Hormones