Starting statins may increase risk of myasthenia gravis onset: Study

Starting statins — widely prescribed medications aimed at lowering levels of the fatty molecule cholesterol — may increase the risk of developing myasthenia gravis (MG) in people across different ethnicities, a new study reported.

The risk appears highest during the first six months of treatment and was more pronounced with higher-intensity statin regimens used in people with a history of heart attack or stroke.

“Considering the rarity of MG as an adverse event, the potential benefits of statin therapy are expected to outweigh the associated risk,” researchers wrote. Still, “consideration of the possibility of new-onset MG may be advisable within the first 6-12 months after initiation of statins, especially for medium-to-high-intensity statin therapy.”

The study, “Myasthenia gravis following the initiation of statin therapy: A multinational self-controlled case series study,” was published in the Journal of Internal Medicine.

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Statins among the most commonly prescribed medications in the world

Statins are among the most commonly prescribed medications in the world, helping to lower cholesterol and reduce the risk of heart attacks and strokes. They are generally safe and effective, but increasing research has highlighted a rare potential side effect: MG.

MG is a chronic autoimmune disorder that affects the communication between nerves and muscles. Symptoms can include drooping eyelids, double vision, and muscle weakness, which in severe cases can affect breathing.

Previous work by a research team in Hong Kong found a potential association between statin use and MG onset, particularly among people older than 60. However, that study focused primarily on a Chinese population and didn’t assess the impact of different levels of statin exposure.

“Therefore, there is a need for further studies with diverse ethnicities and larger sample sizes to provide robust real-world evidence to inform clinical practice,” the researchers wrote.

To address this gap, a team led by the same researchers conducted a new study using electronic health records from 2,267 adults with MG across three countries — Hong Kong, the U.K., and Japan.

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Risk of developing MG higher in first year after starting statins

Participants’ mean age ranged from 50.75 to 59.45 years across the three study sites, and they were followed for a mean of about five to 15 years. For those who took statins, the mean treatment duration ranged from about 2.5 to four years.

Researchers assessed the risk of MG in each patient before and after statin initiation. Under this method, called a self-controlled case series, patients serve as their own controls, eliminating the need to match them with control groups from diverse ethnic populations.

According to a pooled analysis of participants across all three sites, the risk of developing MG was significantly higher in the first year after starting statins than during periods without statin use.

In the first six months, the risk was more than 2.5 times higher, and in the following six months, it was nearly 1.5 times higher. This increased risk was seen consistently in men and women.

The risk of developing MG was no longer increased after the first year of statin use.

Notably, the elevated MG risk was not observed in all regions. In Hong Kong, the risk was more than 4.5 times higher in the first six months and about 1.5 times higher in the following six months. In the U.K, the risk was increased by threefold early on and by more than 1.5 times later in the year. In Japan, however, statin use was not significantly associated with an increased risk of MG.

This “may be due to [variability] in healthcare systems, population age structure, database coverage and case ascertainment across different countries,” the researchers wrote.

“In this multinational [self-controlled case series] study, statin initiation may be associated with a significantly increased risk of incident MG during the first 6-12 months, with a greater magnitude of risk elevation for higher intensity of statin therapy.

Different levels of statin exposure also appeared to influence the risk of MG in the first six months of treatment.

High-intensity statin regimens, often used in people at the highest risk of cardiovascular events — such as those with prior heart attack or stroke — were significantly linked to a nearly fivefold increase in MG risk.

Medium-intensity regimens, commonly prescribed for patients with moderate cardiovascular risk, were significantly associated with a nearly threefold increase. However, no significant association was observed between low-intensity statin regimens, typically used in patients at lower cardiovascular risk or those unable to tolerate higher doses, and MG risk.

Between six months and one year, only medium-intensity statin regimens continued to show a higher MG risk, by 1.5 times.

When looking at individual statins, simvastatin (sold as Zocor, with generics available) was significantly associated with a fourfold higher risk for MG. While the other two evaluated statins, atorvastatin (sold as Lipitor, with generics available) and rosuvastatin (sold as Crestor, with generics available), were linked to an up to threefold higher risk, these findings were not statistically significant, meaning they could be due to chance.

“In this multinational [self-controlled case series] study, statin initiation may be associated with a significantly increased risk of incident MG during the first 6-12 months, with a greater magnitude of risk elevation for higher intensity of statin therapy,” the researchers wrote.