Repetitive nerve stimulation cutoff values for the diagnosis of myasthenia gravis.
Repetitive nerve stimulation (RNS) showing ≥ 10% decrement is considered the cutoff for myasthenia gravis (MG), but this has never been validated. The objective of this study was to find an optimal validated cutoff value for decrement on RNS.



We performed retrospective chart review of patients who had electrophysiological assessment for possible MG from 2013 to 2015.



A total of 122 patients with MG and 182 controls were identified. RNS sensitivities for generalized and ocular MG using the traditional ≥10% cutoff value were 46% and 15%, respectively, for frontalis recordings, and 35% and 19%, respectively, for nasalis recordings. Using a decrement cutoff value of 7% for frontalis and 8% for nasalis increased the sensitivities by 6-11%, with specificities of 95-96%.



For RNS in facial muscles, we suggest a cutoff value of 7-8%, which increases test sensitivity by 6-11%, while preserving high specificity for the diagnosis of MG. Muscle Nerve, 2016 Muscle Nerve 55: 166-170, 2017.
Ellen and Martin Prosserman Centre for Neuromuscular Diseases, Division of Neurology, Department of Medicine, University Health Network, Toronto General Hospital 200 Elizabeth Street, Room 5 EB 309, Toronto, Ontario, Canada, M5G 2C4.
Alon
A
Abraham
Department of Neurology, King Fahad Hospital of the University, University of Dammam, Dammam, Saudi Arabia.
Majed
M
Alabdali
Department of Neurology, King Fahad Hospital of the University, University of Dammam, Dammam, Saudi Arabia.
Abdulla
A
Alsulaiman
Ellen and Martin Prosserman Centre for Neuromuscular Diseases, Division of Neurology, Department of Medicine, University Health Network, Toronto General Hospital 200 Elizabeth Street, Room 5 EB 309, Toronto, Ontario, Canada, M5G 2C4.
Ari
A
Breiner
Ellen and Martin Prosserman Centre for Neuromuscular Diseases, Division of Neurology, Department of Medicine, University Health Network, Toronto General Hospital 200 Elizabeth Street, Room 5 EB 309, Toronto, Ontario, Canada, M5G 2C4.
Carolina
C
Barnett
Ellen and Martin Prosserman Centre for Neuromuscular Diseases, Division of Neurology, Department of Medicine, University Health Network, Toronto General Hospital 200 Elizabeth Street, Room 5 EB 309, Toronto, Ontario, Canada, M5G 2C4.
Hans D
HD
Katzberg
Division of Endocrinology and Metabolism, Department of Medicine, Mount Sinai, Hospital and Lunenfeld Tanenbaum Research Institute, University of Toronto, Toronto, Canada.
Leif E
LE
Lovblom
Ellen and Martin Prosserman Centre for Neuromuscular Diseases, Division of Neurology, Department of Medicine, University Health Network, Toronto General Hospital 200 Elizabeth Street, Room 5 EB 309, Toronto, Ontario, Canada, M5G 2C4.
Vera
V
Bril
D000328:Adult; D000368:Aged; D001703:Biophysics; D004558:Electric Stimulation / Q000379:methods*; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology; D009157:Myasthenia Gravis / Q000175:diagnosis* / Q000503:physiopathology; D012189:Retrospective Studies
myasthenia gravis; repetitive nerve stimulation; sensitivity; single fiber EMG; specificity