J Clin Neurol.  2016 Oct;12(4):482-488. 10.3988/jcn.2016.12.4.482.

Clinical Significance of Repetitive Compound Muscle Action Potentials in Patients with Myasthenia Gravis: A Predictor for Cholinergic Side Effects of Acetylcholinesterase Inhibitors

• Lee HE
• Kim YH
• Kim SM
• Shin HY

• KMID: 2385114
• DOI: http://doi.org/10.3988/jcn.2016.12.4.482

Abstract

BACKGROUND AND PURPOSE
Acetylcholinesterase inhibitors (AChEIs) are widely used to treat myasthenia gravis (MG). Although AChEIs are usually tolerated well, some MG patients suffer from side effects. Furthermore, a small proportion of MG patients show cholinergic hypersensitivity and cannot tolerate AChEIs. Because repetitive compound muscle action potentials (R-CMAPs) are an electrophysiologic feature of cholinergic neuromuscular hyperactivity, we investigated the clinical characteristics of MG patients with R-CMAPs to identify their clinical usefulness in therapeutic decision-making.
METHODS
We retrospectively reviewed the clinical records and electrodiagnostic findings of MG patients who underwent electrodiagnostic studies and diagnostic neostigmine testing (NT).
RESULTS
Among 71 MG patients, 9 could not tolerate oral pyridostigmine bromide (PB) and 17 experienced side effects of PB. R-CMAPs developed in 24 patients after NT. The highest daily dose of PB was lower in the patients with R-CMAPs (240 mg/day vs. 480 mg/day, p<0.001). The frequencies of PB intolerance and side effects were higher in the patients with R-CMAPs than in those without R-CMAPs [37.5% vs. 0% (p<0.001) and 45.8% vs. 12.8% (p=0.002), respectively]. The MG Foundation of America postintervention status did not differ significantly between MG patients with and without R-CMAPs, and the response to immunotherapy was also good in both groups.
CONCLUSIONS
Side effects of and intolerance to AChEIs are more common in MG patients with R-CMAPs than in those without R-CMAPs. AChEIs should be used carefully in MG patients with R-CMAPs. The presence of R-CMAPs after NT may be a good indicator of the risks of PB side effects and intolerance.

Keyword

myasthenia gravis; acetylcholinesterase inhibitor; repetitive compound muscle action potential

MeSH Terms

Acetylcholinesterase*
Action Potentials*
Americas
Cholinesterase Inhibitors*
Humans
Hypersensitivity
Immunotherapy
Myasthenia Gravis*
Neostigmine
Pyridostigmine Bromide
Retrospective Studies
Acetylcholinesterase
Cholinesterase Inhibitors
Neostigmine
Pyridostigmine Bromide

Figure

• 

  Fig. 1 Electrodiagnostic tests of the abductor digiti minimi muscle. A and B: Repetitive compound muscle action potentials (R-CMAPs) were not seen in the baseline electrodiagnostic testing. C and D: R-CMAPs after an intramuscular injection of neostigmine methylsulfate (0.02 mg/kg). During repetitive nerve stimulation at 3 Hz, the repetitive discharges after the first compound muscle action potential were diminished by the second stimulation (D).

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