Is myasthenia gravis a rare disease, or is it just underdiagnosed?

Someone recently left a comment on one of my columns that made me pause and lean in. They wrote that myasthenia gravis (MG) isn’t rare; it’s just underdiagnosed.

Oofta. That one hit like a whisper with a punch. Because on the surface, it feels true. Many of us with MG waited years for a proper diagnosis and were often misread, dismissed, or misunderstood in the meantime. My own journey to diagnosis took seven years. So the idea that MG is just flying under the radar? Sure, it makes sense. But is that the whole story?

What does ‘rare’ even mean?

To figure out if MG is rare or not, we need to understand what’s considered a rare disease. As it turns out, the definition varies depending on where you are in the world.

• In the United States, a disease is considered rare if it affects fewer than 200,000 people.
• In Europe and the U.K., rare diseases are defined as affecting fewer than 1 in 2,000 people.
• In Australia, a condition is deemed rare if it affects 5 or fewer people per 10,000.
• The World Health Organization defines a rare condition as affecting fewer than 65 per 100,000 people.

So where does MG land?

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According to one analysis, in 2021, MG was estimated to affect 37 in 100,000 people in the U.S. That definitely checks the “rare” box — but here’s where it gets juicy.

MG is a master of disguise. Its symptoms — including muscle weakness, droopy eyelids, slurred speech, and fatigue — can look like stroke, multiple sclerosis, depression, or even everyday exhaustion, among countless other conditions. That overlap means a lot of folks are misdiagnosed or simply never diagnosed at all. It’s especially tricky for those of us with seronegative MG, where the usual antibody tests come up clean.

So, yes, the numbers say it’s rare. But I think the real prevalence might be higher than what’s recorded.

Diagnosed more, but still hard to catch

What’s interesting is that, over the last few decades, the incidence and prevalence of MG have more than doubled. More accurate tests, increased awareness, and people living longer with MG have likely played a role. But that doesn’t necessarily mean that a higher proportion of people have it now; it could just mean that more of us are finally being seen and diagnosed. That distinction matters.

OK, but what if MG stops being rare in terms of numbers? Let’s say it tips over that threshold — what then?

Rare diseases tend to have several things in common, such as complex biology, specialized treatments, and limited research and resources. MG definitely checks those boxes!

Managing MG often requires a team of specialists, an individualized treatment plan, consistent monitoring, and frequent adjustments. The disease can be unpredictable, and many general practitioners may not feel confident treating it on their own. MG support, resources, and research are still relatively limited compared with more well-known chronic conditions.

Even if the prevalence rises to the point that MG is no longer considered rare, we’re still dealing with a complex condition that requires personalized care — something we’ll continue to have in common with much of the rare disease community.

So is MG rare? The bottom line is, technically, yes. But it’s also likely that the condition is underdiagnosed; it might not even be considered rare one day. Both can be true at the same time.

And to the person who dropped that comment — you’re not wrong. You just helped spark a deeper conversation. And for that, I’m grateful.

Note: Myasthenia Gravis News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website. The opinions expressed in this column are not those of Myasthenia Gravis News or its parent company, Bionews, and are intended to spark discussion about issues pertaining to myasthenia gravis.