(345) Ocular Vestibular Evoked Myogenic Potentials in Ocular Myasthenia Gravis

Introduction: Diagnosis of Mysthenia Gravis depends on antibody assays, electrophysiologic tests or single-fiber EMG, and edrophonium tests which are all of reduced sensitivity in ocular mysthenia gravis. The extraocular muscles have previously not been directly accessible for clinical testing in MG patients. We therefore assessed an additional application of the oVEMP.

Methods: The study group consisted of 30 patients suffering from localized ocular MG. Diagnosis of MG was made based on the presence of a typical history and at least one positive ancillary test. The control group consisted of 10 subjects that was age and sex matched. No auditory, vestibular or neurological problems. This study was carried out from January 2021 to December 2022. oVEMP testing was done while the patients were tested in a sitting position. Measurements that were performed: n10 latency, n10 threshold, n10 baseline to peak amplitude, n10 amplitude asymmetry ratio.
Statistical analysis: Non parametric Mann Whitney U test for comparison of both the study and the control groups.
P values less than 0.05 were considered to be statistically significant.

Results: n10 latency, n10 threshold, n10 baseline to peak amplitude, n10 amplitude asymmetry ratio were of statistically significant difference between the study and control group (p value < 0.05). In all but one patient, ptosis was asymmetric, with unilateral predominance in 16 patients and strictly unilateral manifestation in 11patients
In 3 patients, the clinical involvement was evident in one eye only (unilateral ptosis, no diplopia), but oVEMP revealed a bilateral affection.
Despite the reduced amplitude, absence of oVEMP response was not seen in this study.

Conclusions: We have demonstrated that a reflex of the extraocular muscles decreases with repetitive vestibular stimulation using the oVEMP technique. oVEMP are capable to demonstrate subclinical MG dysfunctions or sailent lesions as it may directly and noninvasively reveal the pathognomonic fatigability of extraocular muscles. oVEMP assess vestibular brainstem function thus adding insights into the pathogenesis of Mysthenia Gravis.