J Clin Neurol.  2017 Jul;13(3):287-292. 10.3988/jcn.2017.13.3.287.

Repetitive Nerve Stimulation in MuSK-Antibody-Positive Myasthenia Gravis

• Kim SW
• Sunwoo MK
• Kim SM
• Shin HY
• Sunwoo IN

• KMID: 2391673
• DOI: http://doi.org/10.3988/jcn.2017.13.3.287

Abstract

BACKGROUND AND PURPOSE
Responses to repetitive nerve stimulation (RNS) in patients with muscle-specific tyrosine kinase (MuSK) antibody (Ab)-positive myasthenia gravis (MG) vary depending on the muscles tested. We analyzed the RNS responses of limb and facial muscles in MuSK-Ab-positive and acetylcholine receptor (AChR)-Ab-negative MG (MuSK MG) and MuSK-Ab-negative and AChR-Ab-negative [double-seronegative (DSN)] MG patients.
METHODS
We retrospectively compared RNS responses between 45 MuSK MG and 29 DSN MG. RNS was applied to the abductor digiti minimi, flexor carpi ulnaris, trapezius, orbicularis oculi, and nasalis muscles.
RESULTS
Abnormal RNS responses in limb muscles were observed in 22.2 and 58.6% of MuSK MG and DSN MG patients, respectively, with abnormal facial responses observed in 77.8 and 65.5%, and abnormal responses observed in any of the five muscles in 86.7 and 72.4%. Abnormal RNS responses in the abductor digiti minimi or flexor carpi ulnaris were less frequent in MuSK MG (8.9 and 15.6%, respectively) than in DSN MG (37.9 and 55.2%), whereas the findings for other muscles were not significantly different between the groups. Abnormal facial responses but normal limb responses were independently associated with MuSK MG (odds ratio=5.224, 95% confidence interval=1.300-20.990).
CONCLUSIONS
Abnormal RNS responses primarily in facial muscles without involvement of limb muscles were more pronounced in MuSK MG than in DSN MG. RNS of both facial and limb muscles in AChR-Ab-negative MG can increase the test sensitivity and aid in early suspicion of MuSK MG.

Keyword

MuSK; muscle-specific tyrosine kinase; myasthenia gravis; repetitive nerve stimulation; acetylcholine receptor

MeSH Terms

Acetylcholine
Extremities
Facial Muscles
Humans
Muscles
Myasthenia Gravis*
Protein-Tyrosine Kinases
Retrospective Studies
Superficial Back Muscles
Acetylcholine
Protein-Tyrosine Kinases

Figure

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  Fig. 1 Abnormal rate of repetitive nerve stimulation responses depending on the site of examination in (A) muscle-specific tyrosine kinase-antibody-positive myasthenia gravis group and (B) double-seronegative myasthenia gravis group. NA: nasalis, OO: orbicularis oculi, TR: trapezius.

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