Phrenic and intercostal repetitive nerve stimulation: a useful electroneurophysiological method to detect the respiratory status of myasthenia gravis patients.
OBJECTIVE
To get a comprehensive recognition about the profile of phrenic repetitive nerve stimulation (PRNS) and intercostal repetitive nerve stimulation (IRNS) in healthy people, to investigate the electrophysiological features about respiratory function of myasthenia gravis (MG) patients, and to detect the predictive value of IRNS and PRNS on the respiratory deterioration of MG patients during the pulse treatment with large dosage of adrenal corticosteroid.


METHODS
Bilateral PRNS and IRNS with stimulation frequency of 3 and 5 Hz were tested in 28 healthy people and 113 MG patients; limb and cranial repetitive nerve stimulation (RNS), clinical score and forced vital capacity (FVC) were also recorded from those MG patients. Further more, PRNS and IRNS of 36 MG patients were tested 3 days before the beginning of their adrenal corticosteroid pulse treatment, FVC, clinical score and respiratory changes of the MG patients were simultaneously observed.


RESULTS
For healthy people, there were no significant differences in the results of PRNS or IRNS in different age, sex and testing sides. After combining the left result with the right one, the amplitude decrement percentage in PRNS and IRNS was less than 7%. PRNS had more technical difficulty than IRNS. For 113 MG patients, FVC was dependent on the values of PRNS, IRNS and facial RNS. A subclinical respiratory dysfunction was found in patients with type I and II MG. The abnormal rate of PRNS in type IIb MG was similar to that in type III and IV MG, even though a difference in the percentage of amplitude decrement between them was observed. Meanwhile, both the abnormal rate and the percentage of amplitude decrement of IRNS had no difference between type IIb MG and type III and IV MG. The general incidence of abnormal PRNS and abnormal IRNS were higher than those of decreased FVC and clinical dyspnea, and the sensitivity of PRNS in type IIa MG patients was higher than that of IRNS. Among 36 MG patients under the adrenal corticosteroid pulse treatment, 14 showed the newly clinical dyspnea or worsened original one 2 to 13 days after the beginning of the therapy. There were significant difference of the above parameters between the patients with and without respiratory deterioration during the treatment. Logistic regression analysis showed that when the mean value of the bilateral IRNS amplitude decrement was larger than 30%, the odds ratio of the occurrence of the respiratory deterioration was 19.523, for both 3 and 5 Hz stimulation.


CONCLUSIONS
It is recommended that PRNS and IRNS will be defined as abnormal when their amplitude reduces more than 15%. PRNS and IRNS are neurophysiological indices reflecting the damage of respiratory muscles in MG, they are helpful in evaluating the clinical condition correctly and making the classification of MG properly. It is necessary to test the PRNS and IRNS in type II MG patients regularly. Although the respiratory damage during the adrenal corticosteroid treatment was correlated with PRNS, IRNS, FVC, MG clinical score and type, only IRNS had predictive value on the respiratory deterioration during the treatment.
Zhuang
L
L
Department of Neurology, PUMC Hospital, Beijing, 100730. lzhlll@btamail.net.cn
Tang
X
X
Fan
D
D
Xu
X
X
Wang
X
X
Jiang
J
J
D000305:Adrenal Cortex Hormones / Q000008:administration & dosage / Q000627:therapeutic use; D000328:Adult; D000368:Aged; D002648:Child; D005260:Female; D006801:Humans; D007367:Intercostal Nerves / Q000187:drug effects / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000150:complications* / Q000188:drug therapy / Q000503:physiopathology*; D010791:Phrenic Nerve / Q000187:drug effects / Q000503:physiopathology*; D011237:Predictive Value of Tests; D020551:Pulse Therapy, Drug; D012016:Reference Values; D012120:Respiration Disorders / Q000188:drug therapy / Q000209:etiology* / Q000503:physiopathology*; D012129:Respiratory Function Tests; D012720:Severity of Illness Index; D004561:Transcutaneous Electric Nerve Stimulation
D000305:Adrenal Cortex Hormones