The difficulty in confirming clinical diagnosis of myasthenia gravis in a seronegative patient: a possible neurophysiological approach.
In seronegative myasthenia gravis repetitive nerve stimulation and single-fibre EMG have a crucial diagnostic value but they may be negative, particularly in repetitive nerve stimulation studies. We report the case of a 43-year-old patient with generalized seronegative myasthenia gravis with negative 3 Hz repetitive nerve stimulation at Erb's point and voluntary single-fibre EMG in the orbicularis oculi. We also performed 6 and 12 Hz repetitive nerve stimulation at Erb and stimulated single-fibre EMG in the extensor digitorum communis and our findings were pathological. Our data suggest that, for individual patients with an atypical picture characterised by dissociation between a severe clinical pattern and no definite neurophysiological findings on conventional tests, repetitive nerve stimulation with a stimulation rate higher than 3 Hz and/or stimulated single-fibre EMG with an increasing stimulation rate may be helpful.
Institute of Neurology, Catholic University of Sacred Heart, Rome, Italy. p.caliandro@rm.unicatt.it
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P
Caliandro
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Evoli
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Stålberg
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Granata
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Tonali
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Padua
D000328:Adult; D004576:Electromyography / Q000379:methods*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009157:Myasthenia Gravis / Q000097:blood / Q000175:diagnosis* / Q000503:physiopathology*; D004561:Transcutaneous Electric Nerve Stimulation / Q000379:methods*