The difficulty in confirming clinical diagnosis of myasthenia gravis in a seronegative patient: A possible neurophysiological approach

Caliandro, P.; Evoli, A.; Stålberg, E.; Granata, G.; Tonali, P.; Padua, L.

doi:10.1016/j.nmd.2009.09.005

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Volume 19, Issue 12 , Pages 825-827, December 2009

The difficulty in confirming clinical diagnosis of myasthenia gravis in a seronegative patient: A possible neurophysiological approach

P. Caliandro
- Institute of Neurology, Catholic University of Sacred Heart, Rome, Italy
- Fondazioni Don Carlo Gnocchi ONLUS, Rome, Italy
- Corresponding author. Address: Institute of Neurology, Largo F. Vito 1, 00168 Rome, Italy. Tel.: +39 06 30154435; fax: +39 06 35501909.
A. Evoli
- Institute of Neurology, Catholic University of Sacred Heart, Rome, Italy
E. Stålberg
- Department of Clinical Neurophysiology, University Hospital, Uppsala, Sweden
G. Granata
- Institute of Neurology, Catholic University of Sacred Heart, Rome, Italy
P. Tonali
- Institute of Neurology, Catholic University of Sacred Heart, Rome, Italy
- Fondazioni Don Carlo Gnocchi ONLUS, Rome, Italy
L. Padua
- Institute of Neurology, Catholic University of Sacred Heart, Rome, Italy
- Fondazioni Don Carlo Gnocchi ONLUS, Rome, Italy

Received 12 May 2009; received in revised form 28 July 2009; accepted 8 September 2009.

Abstract

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 3Hz repetitive nerve stimulation at Erb’s point and voluntary single-fibre EMG in the orbicularis oculi. We also performed 6 and 12Hz 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 3Hz and/or stimulated single-fibre EMG with an increasing stimulation rate may be helpful.