The Spurious Palsy-Fluctuation of Ocular Myasthenia Gravis Symptoms Characterized by Orthoptics

Although fluctuating muscular weakness is the hallmark of myasthenia gravis (MG), research into it, especially during the course of the day, remains limited. Understanding the dynamics of myasthenic symptoms is essential for diagnosis and anticipatory treatment. Therefore, in this study, we used orthoptic and other established quantitative and subjective methods to measure ocular myasthenia gravis (OMG) symptoms throughout the day, during the course of 2 months, and in response to treatment.

The goal of the study was to determine the change of gaze deviation and ptosis during the course of the day, over 2 months, and 1 hour after pyridostigmine intake. Each subject participated in 3 sessions during the day, 2 follow-up sessions, and 1 measurement before and after pyridostigmine. Measurements included the Quantitative Myasthenia Gravis (QMG) score, palpebral fissure height (PFH) photography, the conventional Hess screen test, and a video Hess screen test using video-oculography. The Myasthenia Gravis Activities of Daily Living score (MG-ADL) was obtained on each assessment day. Sum scores were calculated for the gaze deviations of the inner and outer fields of the conventional and the video Hess screen tests.

Twelve patients were recruited, including 11 patients with ocular and 1 patient with generalized MG (mean age 65.7 years, SD 16.9 years; 11 males). The mean sum scores of both the conventional and the video Hess screen test showed a worsening in the evening, reaching significance in the outer field of the Hess screen test (mean increase 13.4°, SD 15.3°, P = 0.02). Similarly, ptosis also worsened during the day, with a significant decrease in PFH in the evening (mean decrease 0.53 mm, SD 0.55 mm, P = 0.04). Although ptosis improved significantly after pyridostigmine intake (mean increase 0.96 mm, SD 1.05, P = 0.03), no significant changes were observed in the sum deviations of the Hess screen tests ( P = 0.6). Both ptosis and the sum scores generally improved over the 2-month period, even in some patients without any therapeutic adjustments. Correspondingly, the mean QMG and MG-ADL scores decreased.

This prospective cohort study provides insight into the dynamics of OMG, which is crucial for the optimization of diagnostic and therapeutic approaches. Our orthoptic measurements demonstrated the worsening of OMG symptoms after daily activity and a better response of ptosis to pyridostigmine than diplopia. The complexity of this fluctuating disease leads to strong interindividual variability, which requires an individual approach to improve the quality of life of patients with MG.