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Usefulness of Single Fiber EMG for Distinguishing Neuromuscular from Other Causes of Ocular Muscle Weakness

Published online by Cambridge University Press:  18 September 2015

C. Ukachoke ,
P. Ashby ,
A. Basinsk  and
J.A. Sharpe
C. Ukachoke
Affiliation:
Division of Neurology, The Toronto Hospital, University of Toronto, Toronto
P. Ashby*
Affiliation:
Division of Neurology, The Toronto Hospital, University of Toronto, Toronto
A. Basinsk
Affiliation:
Division of Neurology, The Toronto Hospital, University of Toronto, Toronto
J.A. Sharpe
Affiliation:
Division of Neurology, The Toronto Hospital, University of Toronto, Toronto
*
The Toronto Hospital, #EC 8-023, 399 Bathurst Street, Toronto, Ontario, Canada M5T 2S8
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Abstract:

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Consecutive patients (n = 114), who had single fiber electromyography of the frontalis muscles for symptoms suggestive of ocular myasthenia gravis, were followed up for a mean of 14 months (3-64 mos). At follow up, based on strict criteria, 23 patients were classified as having ocular myasthenia gravis, 8 patients were diagnosed as having mitochondrial myopathy or oculopharyngeal dystrophy, 18 patients were found to have other diseases and 65 patients remained without a definite diagnosis. The single fiber electromyography data of these patients were then reviewed. The patients with ocular myasthenia gravis had, on average, more than 7/20 single fiber pairs with jitter > 45 μs and mean jitter of 56 μs. The 8 patients with mitochondrial myopathy or oculopharyngeal dystrophy had an average of 5/20 single fiber pairs with jitter > 45 μs and a mean jittter of 52 μs and could not be separated from the group with ocular myasthenia gravis on the basis of the single fiber electromyography results. The 18 patients with definite other diagnosis had an average of less than 1/20 single fiber pair with jitter > 45 μs and a mean jitter of 25 μs. This group could be clearly separated from the group with ocular yasthenia gravis. We conclude that single fiber electromyelography is useful in the separation of ocular myasthenia gravis from other causes of oculomotor weakness except mitochondrial myopathy and oculopharyngeal dystrophy.

Résumé:

RÉSUMÉ:

Nous avons suivi pendant 3 à 64 mois (moyenne de 14 mois) des patients consécutifs (n = 114) qui ont eu un électromyogramme de fibres uniques des muscles frontaux (EMGFUF) à cause de symptômes suggestifs d'une myasthénie grave (MG) oculaire. Au cours du suivi, 23 patients ont été classifiés comme étant atteints de MG oculaire, 8 patients ont eu un diagnostic de myopathie mitochondriale ou de dystrophic oculopharyngée, 18 patients étaient atteints d'autres maladies et 65 patients n'ont pas reçu de diagnostic définitif. Nous avons revisé les données de l'EMGFUF de ces patients. Les patients avec MG oculaire avaient, en moyenne, plus de 7/20 paires de fibres uniques avec des excitations > 45 μs et une moyenne de 56 μs. Les 8 patients atteints de myopathie mitochondriale ou de dystrophie oculopharyngée avaient en moyenne de 5/20 paires de fibres uniques avec des excitations> 45 μs et une moyenne d'excitations de 52 μs et ne pouvaient pas être distingués du groupe avec MG oculaire à partir des résultats de l'EMGFUF. Les 18 patients avec un diagnostic définitif autre avaient en moyenne moins de 1/20 paire de fibres uniques avec des excitations > 45 μ s et une moyenne d'excitations de 25 μs. Ce groupe peut être distingué clairement du groupe de MG oculaire. Nous concluons que l'EMGFUF est utile pour séparer la MG oculaire des autres causes de faiblesse oculomotrice, sauf de la myopathie mitochondriale et de la dystrophie oculopharyngée.

Type
Articles
Information
Canadian Journal of Neurological Sciences , Volume 21 , Issue 2 , May 1994 , pp. 125 - 128
Copyright
Copyright © Canadian Neurological Sciences Federation 1994

References

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