Decrements in oculomotor ranges after repeated saccadic and pursuit movements may be a sensitive and specific tool for the diagnosis of myasthenia gravis (MG), according to a study published in the Journal of Neurology.
Quantitative analysis of saccadic and smooth pursuit fatigability using video-oculography (VOG) was able to distinguish between patients with MG and healthy controls (HCs; P <.01), the researchers found. Using saccadic decrement cutoffs of greater than 7.2% in the horizontal and greater than 6.4% in the vertical direction in the patients’ more-affected eyes was able to achieve high sensitivity (76.1% for horizontal and 78.3% for vertical) and specificity (100% for horizontal and 95.8% for vertical) when differentiating patients with MG and HCs, the investigators noted.
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Using similar saccadic decrement cutoffs for the less-affected patients’ eyes (>6.7% for horizontal and >7.3% for vertical) was still able to differentiate between patients with MG and HCs with a sensitivity of 54.3% and specificity of 95.8% for horizontal saccades and sensitivity of 63% and specificity of 95.8% for vertical saccades.
Decrements in smooth pursuit were able to discriminate between patients with MG and HCs in the more-affected eyes but not the less-affected eyes, the study team noted.
“We demonstrated the diagnostic utility of quantifying the oculomotor decrements after repetitive saccades and smooth pursuits to reflect sensitively the oculomotor fatigue found in Ms,” the authors wrote.
“This method particularly facilitates diagnosis in patients with isolated ocular involvement, negative serology, and conventional RNS studies. VOG analysis can provide direct evidence of oculomotor fatigability and has unique advantages as a reliable, safe, and simple test,” the authors continued.
During the study, a total of 46 patients with MG were included along with 24 healthy controls. The patient with MG cohort was made up of 35 patients with oculomotor MG and 11 with generalized MG. While no difference in saccadic movements were observed between the patients with MG and HCs at the beginning of the oculomotor tracking tasks, patients with MG began to show decrements around the 10th repeated movement. No differences were observed between the decrements of patients with oculomotor MG and those with generalized MG.
Reference
Nguyen TT, Kang JJ, Chae JH, et al. Oculomotor fatigability with decrements of saccade and smooth pursuit for diagnosis of myasthenia gravis. J Neurol. Published online March 1, 2023. doi:10.1007/s00415-023-11611-7
