Myasthenia Gravis With Presynaptic Electrophysiologic Abnormalities

• Published in: Journal of clinical neuromuscular disease Vol. 10; no. 4; pp. 185 - 190
• Main Authors: Callaghan, Brian, Moster, Mark L, Bird, Shawn J
• Format: Journal Article
• Language: English
• Published: United States Lippincott Williams & Wilkins, Inc 01-06-2009
• Subjects: Action Potentials - physiology; Aged; Biophysics; ELAV Proteins - blood; Electric Stimulation; Electrophysiology - methods; Humans; Male; Myasthenia Gravis - pathology; Myasthenia Gravis - physiopathology; Myasthenia Gravis - surgery; Neural Conduction - physiology; Peripheral Nerves - physiopathology; Reaction Time - physiology; Receptors, Cholinergic - immunology; Thymectomy - methods; Young Adult
• ISSN: 1522-0443; 1537-1611
• DOI: 10.1097/CND.0b013e3181a347ff

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.