Summary Introduction The aim of this study was to define the diagnostic accuracy of concentric needle (CN)-jitter in newly diagnosed myasthenia gravis (MG) patients and to compare CN-jitter with repetitive nerve stimulation. Methods In 30 MG patients, repetitive nerve stimulation in 4 muscles (orbicularis oculi, nasalis, trapezius and abductor digiti minimi) and CN-jitter of extensor digitorum (ED) and frontalis muscles were evaluated. Results Twenty-eight of 30 patients (93%) had high jitter in at least one muscle. Repetitive nerve stimulation was abnormal in 23 of the patients (77%). Eighty-six percent of the patients in whom repetitive nerve stimulation test was negative could be diagnosed with CN-jitter. The most frequent muscle showing abnormal decrement was orbicularis oculi. The results of CN-jitter were similar between patients with different serological groups. Of 13 patients with generalized weakness, all had high jitter in both muscles studied whereas of 17 patients only with ocular weakness, 15 had high jitter in at least one muscle studied. Conclusion Abnormal RNS was present in 77% of newly diagnosed MG patients, being less than CN-jitter (93%) but more than antibody positivity (73.3%).
