Associations Between Clinical Severity, Serological Testing, and Electrophysiological Profiles in Patients with Myasthenia Gravis
Ladan Bigdeli1, William Arnold2, Kristina Kelly1, Bakri Elsheikh1, Jordan Mizell1, Samuel Paul1
1The Ohio State University Wexner Medical Center, 2NextGen Precision Health, University of Missouri
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.

 

10.1212/WNL.0000000000201796