While a number of factors may influence the conversion of ocular myasthenia gravis (MG) to generalized MG, smoking both increases the risk of conversion and accelerates the conversion timeline, according to a study recently published in the Journal of Ophthalmology.
Studies suggest that most patients initially diagnosed with ocular MG develop generalized MG within two years, but scientists are still unsure about exactly how and why conversion takes place.
Researchers thus conducted a study in which they analyzed the data of 200 patients who had been diagnosed with ocular MG at a Thai hospital. The study period was between January 2007 and December 2019. All patients were monitored either until they developed generalized MG or until their last follow-up visit, whichever came first.
Of the 200 patients, 78 (39%) developed generalized MG over a median follow-up period of 16 months. Researchers found a number of factors that correlated with conversion from ocular to generalized MG. These included a history of smoking, the presence of thymic abnormalities and positive acetylcholine receptor antibodies.
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Smoking was found to both increase the likelihood of conversion from ocular to generalized MG and to speed up this conversion. The authors suggested this may be due to smoking’s effects on the immune system, as well as blood nicotine impacting the neuromuscular junction.
“Based on these insights, we recommend that patients with myasthenia gravis cease smoking to mitigate the risk of progression to GMG and to ameliorate the severity of symptoms associated with OMG and GMG,” the study’s authors noted.
The authors also found that pyridostigmine (a therapy used in MG) dose greater than 180 mg/day was associated with disease progression. However, they noted that higher pyridostigmine dose may indicate a patient had more severe disease, rather than increase the risk of progression itself.
“In summary, our findings expand on previous research by incorporating a larger and more diverse cohort, analyzing novel predictors,” the authors of the study wrote. “Future research efforts should be directed toward executing randomized controlled trials or prospective studies to substantiate our findings.”
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