Diagnostic Value Study Of Post-exercise Repetitive Nerve Stimulation In Patients With Myasthenia Gravis

Objective:To analyze the changes of post-exercise repetitive nerve stimulation(RNS)in patients with myasthenia gravis(MG),aim to explore more sensitive electrophysi-ological diagnostic techniques for myasthenia gravis.Method:A total of 33 patients with clinically diagnosed MG were collected in our study.Among them,9 patients were generalized myasthenia gravis(GMG)and 24 patients of ocular myasthenia gravis(OMG).Firstly all the people underwent routine RNS test in orbicularis oculi,trapezius and abductor digiti quinti muscle with low frequency(3Hz)supramaximal current.And then,1-minute exercise test was performed in orbicularis oculi,trapezius and abductor digiti quinti muscle.Then the post-exercise RNS test at the same frequency was performed again in all muscles.The record of routine RNS and post-exercise RNS which was performed on orbicularis oculi,trapezius and abductor digiti quinti muscle at rest state and after 1-minute exercise respectively were collected and compared.Result:In the 9 GMG patients,there was no significant difference of the separate and total positive rate of between the routine RNS and post-exercise RNS(P=0.025 ~ 1).As for decreased level of the fourth wave of compound muscle action potential(CMAP)compared to the first wave amplitude,when stimulating the orbicularis oculi and trapezius muscle,the post-exercise group displayed more obvious decrease than routine group(P=0.008 and P=0.021),while the abductor digiti quinti muscle showed no difference(P=0.068).In the 24 OMG patients,the separate and total positive rate of the post-exercise RNS were significantly higher than routine group(P=0.004~0.05).As for decreased level of the fourth wave of CMAP,all of the three muscles revealed a more evident decline of the post-exercise group than another group(P=0.002~0.006).Compared the positive rate in different muscles after 1-minute exercise and decreasing rate of the 4th wave of CMAP compared to the first wave amplitude,all of the 33 patients showed significant higher positive rate in the orbicularis oculi and trapezius muscle than the abductor digiti quinti muscle(P=0.001~0.05),with no significant difference between orbicularis oculi and trapezius muscle(P=0.564~1).Conclusion:The post-exercise RNS showed higher positive rate in OMG diagnosis than routine RNS,but no difference in GMG diagnosis.The exercise test can significantly improve the diagnostic sensitivity of RNS in orbicularis oculi and trapezius muscle than the abductor digiti quinti muscle in both OMG and GMG.