With most previous studies on ocular myasthenia gravis stemming from investigations the neurology field, the present investigators came to their conclusion via neuro-ophthalmic analysis.
In the absence of a standardized definition of ocular myasthenia gravis (OMG) from established diagnostic criteria, researchers of a new retrospective, single-center study say that OMG should be considered in patients with both ptosis and diplopia, particularly vertical diplopia.
Further, they suggest that high acetylcholine receptor auto-antibody (AchR Ab) titer, severe ocular symptoms, and abnormal thymic lesions may be associated with poor prognosis and secondary general MG (GMG). They published their findings in Medicine (Baltimore).
“Approximately 50% to 60% of patients with MG initially present with ocular symptoms such as ptosis, diplopia, and ophthalmoplegia. Moreover, 50% to 60% of patients presenting with OMG subsequently progress to GMG, commonly within the first 1 to 2 years,” commented the researchers. “Thus, early changes are readily detected by ophthalmologists in many patients. However, the diagnosis of OMG based on clinical findings is often challenging because OMG should be considered in the differential diagnosis of any pattern of painless, unilateral or bilateral, pupil-sparing ophthalmoplegia with or without ptosis.”
The researchers followed 28 patients with ptosis and/or diplopia for at least 6 months, all of whom were AchR Ab–positive or responded to an antimyasthenic regimen. Throughout follow-up, the researchers found that 18 patients had positive OMG results, 16 of whom were seropositive for AchR Ab and 2 of which were seronegative with positive repetitive nerve stimulation test findings. All 8 patients who had both ptosis and diplopia and all 7 patients with abnormal thymic lesions had positive results.
Abnormal thymic lesions were also more common among patients with AchR Ab titer over 5 nmol/L than among patients with AchR Ab titer under 5 nmolo/L (66.67% vs 11.11%). Among the 18 patients who had positive results, half had an AchR Ab titer under 5 nmol/L and half had an AchR Ab titer over 5 nmol/L. Both horizontal and vertical diplopia was significantly higher in patients with AchR Ab titer over 5 nmol/L.
“Interestingly, all patients had normal thymus without any abnormal thymic lesions (thymus hyperplasia, thymoma) in the negative-result OMG group. This result suggests that thymic lesions are associated with a positive AchR Ab,” explained the researchers. “The negative result group had milder symptoms with a normal thymus and responded well to pyridostigmine treatment. Some patients in this group might have had other types of Abs. A recent study evaluated 62 GMG patients who were MG seronegative for AchR Ab and found that 27.4% of patients were positive for Musk (Muscle-specific tyrosine kinase) Ab and 3.2% for LRP4 (LDL-related receptor-related protein 4) Ab.”
The researchers also compared ocular symptoms between the group of patients with both ptosis and diplopia and patients with one or the other. They found that patients with both symptoms were more likely to have horizontal and vertical diplopia (75% vs 7.14%), experience GMG conversion, and need steroids than patients with ptosis or diplopia. The grade of ptosis, angle of deviation, AchR Ab titer, and ice test results were not significantly different between the groups.
“The strength of this study is the clinical data on ocular symptoms provided by neuro-ophthalmologists in a standardized pattern and information on clinical examination from a single institution,” the study investigators concluded. “after excluding of cranial nerve palsy, if there is ptosis and diplopia, especially vertical diplopia, the possibility of OMG should be considered.”
Kim D, Roh H, Oh S. Ophthalmologic clinical features of ocular myasthenia gravis. Medicine. 2023;102(2):e31972. doi:10.1097/MD.0000000000031972