Electrophysiological study of neuromuscular system involvement in mitochondrial cytopathy

Objectives: To define the neuromuscular involvement in 'mitochondrial' pati ents with clinical evidence of a neuromuscular disorder, and to evaluate if the proposed electrophysiological protocol was suitable to reveal a subcli nical neuropathy or myopathy in 'mitochondrial' patients with no clinical s ign of a neuromuscular disturbance. Methods: Quantitative concentric needle electromyography (CNEMG), single fi ber electromyography (SFEMG) and nerve conduction studies (NCS) were perfor med in 33 patients with mitochondrial cytopathies. Lastly, we studied 9 cli nically 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 th e electrophysiological studies. Conclusions: Electrophysiological findings did not correlate with any speci fic biochemical or genetic defect, but were consistent with clinical diagno sis in almost all of the patients with clinical signs of myopathy and/or ne uropathy. Increase of both SFEMG jitter and fiber density was significantly tied to a neuropathic process. CNEMG and SFEMG were altered in about 30% o f subjects without clinical signs of myopathy or neuropathy and were theref ore able to reveal a subclinical involvement of neuromuscular system in som e patients who had external ophthalmoplegia or retinitis only. (C) 1999 Els evier Science Ireland Ltd. All rights reserved.