Single-Fiber Electromyography of Single-Fiber Electromyography of the Trapezius in Patients with Myasthenia Gravis Safaa Hussein Ali PhD

  • imj Iraq Medical Journal
Keywords: Single-fiber electromyography, Trapezius, Myasthenia gravis, Repetitive nerve stimulation.


Background: Myasthenia gravis is a chronic autoimmune disease of the neuromuscular junction, clinical and electrophysiological assessment of muscles is necessary for the diagnosis. Repetitive nerve stimulation test is reliable and its sensitivity depends on the distribution and the severity of the affected muscles.

Objective: This study aimed to characterize the normal values of jitter for volitional singlefiber electromyography (SFEMG) of the upper trapezius in healthy subjects and patients with generalized myasthenia gravis in Iraq. Methods: Fifty-two patients with myasthenia gravis (mean age, 34.8 years; mean duration of illness, 4.1 years) underwent single-fiber electromyography of the trapezius, frontalis, and extensor digitorum communis (EDC) muscles. In addition, for the control group, 30 healthy subjects (mean age, 32.8 years) were subjected to single-fiber electromyography of the trapezius. Results: The mean jitter of the trapezius in the patient group (67.1 ± 8.7 µs) was significantly higher than that in the control group (18.7 ± 4.1 µs; p < 0.001). The normal upper limit of trapezius mean (Mean consecutive differences) MCD of 23 µs /study (mean ± 1 standard deviation) and 26 µs per individual fiber pair, respectively (95th upper percentile, 26.4 µs). Conclusion: These results suggest that volitional SFEMG of the trapezius is a specific investigation for diagnosis of generalized myasthenia gravis even when the examined muscle is not clinically weak. Because of relatively poor patient tolerance and a remote risk of accidental pneumothorax, it is not advisable to examine the upper trapezius


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