DEAR DR. ROACH: I'm a 75-year-old woman who is active in many ways. I did the swimming leg for a triathlon female relay team, which was 2-3 miles in the open ocean.

So, I am baffled by my recent diagnosis of myasthenia gravis (MG)! Reading as much as possible for a clue, I found a (nonvalid) study stating that seniors who began taking statins mysteriously came down with MG. I began Crestor in April 2022.

The seniors in the study were switched to non-statin cholesterol medications, and their symptoms subsided. MG is not listed as a "risk factor" for any statin. What does your research say? -- N.C.

ANSWER: Hundreds of thousands of people start statin drugs each year, and just by chance, they might also get illnesses that could lead them to think the statin might have caused it. So, it can be difficult to determine whether the statin really caused the problem.

I did read some case reports of older people who developed MG (an autoimmune disease of the junction of the nerve and muscle, leading to muscle weakness) within weeks of starting a statin. The fact that yours started two years after starting Crestor makes the association seem more likely due to chance than Crestor.

I have read that as many as 10% of people see a worsening in the disease if they start a statin. If this is the case, the statin should be stopped. I also read that a drug that shouldn't affect the muscles at all -- ezetimibe (Zetia), which works by reducing absorption of cholesterol from the diet -- was also associated with the worsening of MG in one case. It got better when the medication was stopped.

Statin drugs modestly reduce the risk of vascular disease complications, including stroke, heart attack and death, when given to people at a higher risk. The greater a person's risk of heart attack and stroke, the more benefit there will be from taking a statin. The data for the prevention of heart disease in 75-year-old women who don't have a known heart disease isn't strong, but most experts in the field believe that statins have some benefit.

Still, the potential benefit needs to be weighed against the possible risks. The risk of developing MG isn't large enough to be a significant consideration when starting a statin, but in people who already have MG, it would be wise to watch for worsening of MG symptoms, such as double vision or muscle weakness.

Other options to reduce cholesterol with less risk to the muscles include bile acid sequestrants, which are very safe but may not do much to reduce heart risks. PCSK-9 inhibitors, like evolocumab (Rapatha), were shown in one study to have no increased risk of muscle damage, despite case reports of the disease worsening. Bempedoic acid (Nexlotol) is a new cholesterol medicine with much less risk of muscle damage, but I couldn't find any data involving people with MG.