To evaluate Stimulated jitter analysis (Stim-JA) among children with neuromuscular junction (NMJ) disorders.

Stim-JA is a rapid neurophysiological test to evaluate NMJ transmission. It involves stimulation of the distal branch of the facial nerve with a monopolar needle electrode. Time variability of muscle fiber action potentials (jitter) is recorded from orbicularis oculi muscle using a concentric needle electrode. Stim-JA is a preferred test for children, who often have difficulty making controlled activations. However, there is a paucity of literature detailing the mean jitter and % abnormal apparent single fiber action potentials (ASFAPs) between normal and abnormal Stim-JA studies.

Retrospective analysis of 227 studies performed in the pediatric electrodiagnostic laboratory at Children’s Healthcare of Atlanta from 2014 to 2021. Mean age of the participants was 8.6 ± 5.9 years (133 girls and 94 boys). Studies having two or more ASFAPs with jitter values ≥ 34 μs and/or any blocking were categorized as abnormal. Serum anti-AchR receptor and Myasthenia Gravis Foundation of America (MGFA) score were recorded.

Thirty percent studies (n=68) with mean jitter values of 13.2 ± 4.8 μs (range 1.29-21.8 μs) were normal. Seventy percent studies (n=159) with mean jitter values of 33.5 ± 17.1 μs (range 8.33-95.6 μs) were abnormal. Difference in mean jitter was statistically significant (p<0.001). Percent abnormal ASFAP’s was significantly different between normal (2.2%, range 0-10%) and abnormal (55%, range 9-100%) studies (p<0.001). Eleven (16%) normal studies showed seropositivity while 96 (60%) of abnormal studies showed seropositivity. MGFA severity scores differed significantly between normal (mean 0.5 ± 0.8, range 0-5) and abnormal (mean 1.5 ± 0.9, range 0-5) studies (p<0.001).