Orbicularis Oculi Stimulated Jitter Analysis in Children With Autoimmune Myasthenia Gravis

Stimulated jitter analysis (stim-JA) involves analyzing the variation in time intervals between stimulations and action potentials, expressed as the mean consecutive difference (MCD). The MCD upper limits are derived from adult populations and warrant a re-evaluation in children to accurately diagnose neuromuscular junction (NMJ) defects.

A retrospective chart review was conducted which analyzed orbicularis oculi stim-JA studies performed on children between January 2014 and December 2021. The clinical profile, acetylcholine receptor (AChR), and muscle-specific kinase (MuSK) antibody status as well as stim-JA study results were retrieved. Bootstrapping was applied to the stim-JA studies to derive de novo MCD upper limits.

Twenty-seven stim-JA studies were performed on patients aged 3-19 years with either definite myasthenia gravis presentations and NMJ defects (n = 19, 17 AChR+, 2 MuSK+) or those with normal neurological examinations who were seronegative (n = 8). Four hundred ninety-nine apparent single fiber action potentials (ASFAPs) were analyzed with the individual and mean MCD significantly higher in children with autoimmune myasthenia (p < 0.05). Bootstrapping analysis revealed that MCD upper limits of 39 μs for individual MCD and 24 μs for mean MCD significantly improved specificity (p < 0.05) while maintaining sensitivity of the test in distinguishing definite MG NMJ defect from normal NMJ function.

Stim-JA using revised upper limits may help clinicians avoid the over-diagnosis of NMJ disorders in children. Stim-JA is a safe and well-tolerated method to screen for definite MG in children over 2 years.