Abstract Details

Title Associations Between Clinical Severity, Serological Testing, and Electrophysiological Profiles in Patients with Myasthenia Gravis

Topic Neuromuscular and Clinical Neurophysiology (EMG)

Presentation(s) P2 - Poster Session 2 (11:45 AM-12:45 PM)

Poster/Presentation
Number 10-007

Objective

To investigate associations between clinical severity, serological titers, and electrodiagnostic (EDX) profiles in myasthenia gravis (MG).

Background

Compound muscle action potential (CMAP) is an electrodiagnostic (EDX) test that quantifies muscle excitation following single nerve stimulation. CMAP decrement following repetitive nerve stimulation (RNS) is used to assess neuromuscular junction (NMJ) transmission in disorders such as myasthenia gravis (MG). Single fiber electromyography (SFEMG) is a more sensitive NMJ test but is less commonly used for the diagnosis of MG in clinical practice.

Design/Methods

A retrospective chart review was performed. Patients meeting the following criteria were included: age >18 years and MG diagnosis. Data analyzed included acetylcholine (AChR) antibody titer, EDX (CMAP, RNS, SFEMG) of the hand, trapezius, and fascial muscles, and the MG Foundation of America (MGFA) classification of clinical severity.

Results

52 patients (18 male/34 female; age: 55 +/- 16 years, range: 20-81 years) were stratified into ocular-MGFA 1 (n=8m/12f); mild generalized-MGFA 2 (n=7m/15f); and moderate-severe generalized-MGFA 3-5 (n=3m/4f) groups. CMAPs (hand, trapezius, and facial) showed significant differences between MGFA groups (more severe=smaller CMAP) (one-way ANOVA, p<0.05). RNS and SFEMG were similar between groups. AChR titer was similar across MGFA groups and showed a negative correlation with average RNS decrement (hand, trapezius, and facial) (Spearman, p<0.05) but not CMAP or SFEMG.

Conclusions Findings of correlations between MGFA and CMAP, but not other standard MG diagnostics (RNS, SFEMG, AChR titers), was unexpected. Loss of CMAP with more severe disease may indicate that functional impairment in MG is driven by the accumulation of silent NMJs (complete failure of NMJ transmission) rather than variable failure as detected with RNS and SFEMG. Interestingly, AChR titer and RNS decrement were correlated suggesting a relationship between the presence of AChR antibodies and variable NMJ function. Future, prospective studies could investigate CMAP as a biomarker of disease activity and response to treatment.

Authors/Disclosures
Ladan Bigdeli PRESENTER	Mrs. Bigdeli has nothing to disclose.
William D. Arnold, MD	Dr. Arnold has received personal compensation in the range of $5,000-$9,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Genentech. Dr. Arnold has received personal compensation in the range of $5,000-$9,999 for serving on a Scientific Advisory or Data Safety Monitoring board for La Hoffmann Roche. Dr. Arnold has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Cadent Therapeutics . Dr. Arnold has received personal compensation in the range of $0-$499 for serving on a Scientific Advisory or Data Safety Monitoring board for Novartis. The institution of Dr. Arnold has received research support from NIH. The institution of Dr. Arnold has received research support from NMD Pharma. The institution of Dr. Arnold has received research support from Gilead Sciences. The institution of Dr. Arnold has received research support from CureSMA. Dr. Arnold has received intellectual property interests from a discovery or technology relating to health care.
Kristina M. Kelly, PT (The Ohio State University)	Dr. Kelly has nothing to disclose.
Bakri Elsheikh, MD, FAAN (The Ohio State University Wexner Medical Center)	Dr. Elsheikh has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Biogen . Dr. Elsheikh has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Argnex . The institution of Dr. Elsheikh has received research support from Biogen. The institution of Dr. Elsheikh has received research support from Cure SMA.
	No disclosure on file
	No disclosure on file

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