Myasthenia Gravis With Presynaptic Electrophysiologic Abnormalities

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Abstract

Objectives:

To describe the clinical, serologic, and electrophysiologic features of 2 patients with myasthenia gravis (MG), who also had presynaptic electrophysiologic abnormalities.

Methods:

Case reports.

Results:

Two patients developed clinical symptoms consistent with MG. They lacked autonomic symptoms or signs, and their reflexes were not absent. Acetylcholine receptor antibody studies were positive, but assays for voltage-gated calcium channel antibodies were negative. Low-amplitude baseline compound muscle action potentials combined with large incremental responses immediately after exercise were consistent with a presynaptic disorder. Thymic pathology in 1 patient was characteristic of autoimmune MG showing lymphoid follicular hyperplasia. No underlying malignancy was found in either patient.

Conclusions:

Patients with MG may rarely have presynaptic electrophysiologic abnormalities. This may occur even in the absence of the typical clinical and serologic features of the Lambert-Eaton syndrome. It is possible that there is another antibody present that is modulating presynaptic acetylcholine release.

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