Masseteric repetitive nerve stimulation in the diagnosis of myasthenia gravis.
OBJECTIVE
(1) to develop a method for masseteric repetitive nerve stimulation (RNS) and to obtain normative data for amplitude and area decrement of the muscle (M) response. (2) To investigate myasthenia gravis (MG) patients with masseteric RNS. Masticatory muscles are frequently affected in MG, but no RNS test is available to investigate this district.


METHODS
Fifteen healthy subjects and 17 MG patients were examined. The masseteric nerve was stimulated by a monopolar needle (cathode), inserted between the mandibular incisure and the zygomatic arch, and a surface electrode (anode), on the contralateral cheek. Masseteric M response was recorded using surface electrodes on the muscle belly and below the mandibular angle. Stimuli were delivered at 3 Hz in trains of 9, at rest and after isometric effort.


RESULTS
Normal subjects: mean amplitude decrement was 0.3+/-1.2% at rest, and 1.9+/-1.3% after isometric effort.


METHODS
15 patients (88%) were positive on masseteric RNS; in 3 of these it was the only positive RNS test. The extent of decrement observed in masseter muscle was significantly greater than in trapezius muscle.


CONCLUSIONS
Masseteric RNS is a simple and well-tolerated procedure; it offers a new possibility in testing the cranial muscles in disorders of neuromuscular transmission.
Pavesi
G
G
Istituto di Neurologia, Università di Parma, Strada del Quartiere n.443100, Parma, Italy. neurophy@unipr.it
Cattaneo
L
L
Tinchelli
S
S
Mancia
D
D
D000055:Accessory Nerve / Q000503:physiopathology*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005154:Facial Nerve / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008406:Masseter Muscle / Q000503:physiopathology*; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000175:diagnosis / Q000503:physiopathology*; D011446:Prospective Studies; D004561:Transcutaneous Electric Nerve Stimulation / Q000379:methods*; D014459:Ulnar Nerve / Q000503:physiopathology*