This is a call to action for neuro-ophthalmologists and neurologists to collaborate in creating a rating scale for ocular myasthenia gravis (OMG). A rating scale will allow us to all “be on the same page” and will facilitate monitoring patient cases, evaluate response to treatment, and design clinical trials. Just think of how valuable the Frisen grading scale is in following patients with papilledema and how it was incorporated into the Idiopathic Intracranial Hypertension Treatment Trial. Another example is the widely used Glasgow Coma Scale: easy to use and relevant for both clinical management and research (1).
For this discussion, OMG is defined as a patient having only ophthalmic manifestation without symptom or signs of generalized disease. Currently, rating scales emphasize clinical aspects of generalized myasthenia gravis. Ophthalmic measures in both the Quantified Myasthenia Gravis (QMG) rating scale (2) and the Myasthenia Gravis Composite (MGC) scale (2,3) are limited. The ocular components of the QMG scale assess diplopia on lateral gaze, ptosis, and orbicularis oculi strength. Severity of diplopia and ptosis are graded according to the need for provocation of signs, that is, signs present spontaneously; after sustained gaze for 1–10 seconds, 11–60 or >60 seconds. The MGC scale, developed in 2010, evolved from the QMG scale. The 3 questions are similar to the QMG scale, except from the upper limit of timed provocation of diplopia or ptosis, which is reduced from 60 to 45 seconds. Nevertheless, these 3 questions do not sufficiently quantify severity of OMG.
As an initial step in creating a rating scale for OMG, Saleem and I prospectively evaluated 65 patients using a patient-rated questionnaire and an expanded version of the MGC scale (4). We found that the Visual Function Questionnaire (VFQ-25) and the neuro-ophthalmic supplement of the VFQ-25 did not provide useful information for our patient cohort. Similarly, researchers in strabismus have not been satisfied with the VFQ-25 (5).
An ideal rating scale for monitoring of OMG should be quick and easily administered without the need for specified equipment or extensive training. The scale should take into account fluctuations of disease, that is, capturing the overall symptoms outside of the confines of a single clinic visit; this would be best accomplished with patient-rated questionnaires. In addition, a physician-rated component must be included to reduce bias from patients who are excessively positive or negative in their responses.
The rating scale should take into account functionally important aspects of the condition, that is, how diplopia and ptosis affect daily activities, as opposed to simply measuring the clinical deficit. For example, diplopia in primary position or downgaze, or ptosis that obscures the pupil, is more important to daily living than diplopia present only in eccentric gaze or mild ptosis that does not affect vision. To this end, researchers in strabismus have designed tools to measure the field of singular binocular vision, using equipment such as the Goldmann and Octopus machines (6,7), or headsets for cervical range of motion (5). These methods are not widely used due to limited availability. I have been using the Diplopia Questionnaire (8) for monitoring my patients with OMG, and found this useful in monitoring the functional impact of diplopia, and addresses limitations of clinical examination due to fluctuations of disease.
As neuro-ophthalmologists, we have a unique opportunity to develop a usable and representative rating scale for monitoring our patients with OMG. A collaborative working group including both neuro-ophthalmologists and neurologists will allow us to combine our expertise much like the neurologists with expertise in neuromuscular disease created the rating scales and recommendations for clinical trials in patients with generalized myasthenia gravis.
I look forward to hearing if you are interested in being part of a working group to create this important and much needed rating scale.
The author thanks Drs. Eric Eggenberger, Wayne Cornblath, and Gordon Plant for ongoing discussions and collaborations on developing a suitable rating scale, Dr. Jonathan Holmes for ongoing helpful discussions, and numerous NANOS members who have been supportive in the development of this project. Since writing this paper, the author has been in contact with Dr. Carolina Barnett Tapia at the forefront of redesigning MG rating scales, and thanks her for helpful discussions and guidance.
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3. Burns TM. The MG composite: an outcome measure for myasthenia gravis for use in clinical trials and everyday practice. Ann N Y Acad Sci. 2012;1274:99–106.
4. Saleem A, Wong SH. Quantifying severity of ocular myasthenia gravis for research studies. Presentation at the North American Neuro-ophthalmology Society Annual Meeting, April 2017, Washington, DC.
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