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Myasthenia gravis with presynaptic electrophysiologic abnormalities
Brian Callaghan1, Mark L Moster, Shawn J Bird
1Department of Neurology, University of Michigan, Ann Arbor, MI, USA.
Journal of Clinical Neuromuscular Disease
|June 5, 2009
Summary
Myasthenia gravis (MG) patients can rarely exhibit presynaptic electrophysiologic abnormalities, even without Lambert-Eaton syndrome features. This suggests a potential novel antibody affecting acetylcholine release.
Area of Science:
- Neurology
- Clinical Electrophysiology
Background:
- Myasthenia gravis (MG) is an autoimmune disorder affecting neuromuscular transmission.
- Presynaptic disorders, like Lambert-Eaton myasthenic syndrome (LEMS), typically involve voltage-gated calcium channels.
Observation:
- Two patients presented with clinical and serologic findings of MG.
- Electrophysiologic testing revealed low-amplitude compound muscle action potentials with significant post-exercise facilitation, indicative of a presynaptic abnormality.
- Neither patient had autonomic dysfunction or absent reflexes, and voltage-gated calcium channel antibodies were negative.
Findings:
- The patients demonstrated acetylcholine receptor antibodies, confirming MG.
- The electrophysiologic profile suggested a presynaptic disorder, distinct from typical LEMS.
- One patient had thymic lymphoid follicular hyperplasia, common in autoimmune MG.
Implications:
- Rare cases of MG may present with presynaptic electrophysiologic abnormalities.
- This presentation can occur without the characteristic clinical or serologic markers of LEMS.
- The findings suggest the potential involvement of an unidentified antibody modulating presynaptic acetylcholine release in some MG patients.
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