Electrophysiological study of neuromuscular system involvement in mitochondrial cytopathy

Clin Neurophysiol. 1999 Jul;110(7):1284-9. doi: 10.1016/s1388-2457(98)00041-8.


Objectives: To define the neuromuscular involvement in 'mitochondrial' patients with clinical evidence of a neuromuscular disorder, and to evaluate if the proposed electrophysiological protocol was suitable to reveal a subclinical neuropathy or myopathy in 'mitochondrial' patients with no clinical sign of a neuromuscular disturbance.

Methods: Quantitative concentric needle electromyography (CNEMG), single fiber electromyography (SFEMG) and nerve conduction studies (NCS) were performed in 33 patients with mitochondrial cytopathies. Lastly, we studied 9 clinically unaffected relatives.

Results: NCS were abnormal in 18% of patients, with CNEMG and SFEMG in 58% of cases, but there was not a complete overlapping of the positivity of the different techniques. No asymptomatic relatives showed abnormalities of the electrophysiological studies.

Conclusions: Electrophysiological findings did not correlate with any specific biochemical or genetic defect, but were consistent with clinical diagnosis in almost all of the patients with clinical signs of myopathy and/or neuropathy. Increase of both SFEMG jitter and fiber density was significantly tied to a neuropathic process. CNEMG and SFEMG were altered in about 30% of subjects without clinical signs of myopathy or neuropathy and were therefore able to reveal a subclinical involvement of neuromuscular system in some patients who had external ophthalmoplegia or retinitis only.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Electromyography / methods
  • Female
  • Humans
  • Male
  • Middle Aged
  • Mitochondrial Myopathies / physiopathology*
  • Muscles / physiopathology
  • Neural Conduction / physiology*