Study of the Week: Understanding the Natural History of Anti-MuSK Positive Myasthenia Gravis

Welcome to Study of the Week from Patient Worthy. In this segment, we select a study we posted about from the previous week that we think is of particular interest or importance and go more in-depth. In this story we will talk about the details of the study and explain why it’s important, who will be impacted, and more.

If you read our short form research stories and find yourself wanting to learn more, you’ve come to the right place.


This week’s study is…

Spotlight on MuSK positive myasthenia gravis: clinical characteristics, treatment and outcomes

We previously published about this research in a story titled “Study: Understanding The Clinical Course of MuSK-positive Myasthenia Gravis” which can be found here. This study was first published in the scientific journal BMC Neurology. You can view the full text of the study here.

What Happened?

The mechanism of myasthenia gravis, a rare disease, is autoimmune in nature. The immune system produces antibodies that prevent normal communication between the nerves and muscles. In a small number of cases, the system produces antibodies which target a protein called muscle-specific kinase (MuSK), leading to symptoms of myasthenia gravis. In this study, scientists from China analyzed 21 cases of MuSK-positive myasthenia gravis in order to gain a greater understanding of the clinical course of this less common form of the illness.

These 21 cases were from patients who received treatment at the same center from January 2012 to January 2021. The analysis revealed several interesting characteristics about this form of myasthenia gravis. First and foremost, 81 percent of these patients were women, suggesting that they may be at higher risk of MuSK-positive disease than men. Average age of symptom onset was 51.86 years. For this group, the median follow up time was 1134.05 days, or slightly more than three years. The most common initial symptom was ptosis (droopy eyelids), which appeared first in 28.6 percent of patients. Other common symptoms at onset were double vision (23.8 percent), problems swallowing (19 percent), and problems speaking (19 percent).

Patients could be categorized by where symptoms manifested first: Ocular onset (47.6 percent), bulbar onset (42.9 percent), and generalized (9.5 percent). The researchers found that patients with ocular symptoms all progressed to generalized symptoms, with progression occurring in an average of four months. Six patients also suffered a myasthenia gravis crisis, in which symptoms began to affect breathing and became life threatening. Median time to progression was 7.76 months.

As for treatment, 81 percent were treated with pyridostigmine and over 90 percent were treated with immune suppressors, such as steroids. The majority received more than one therapy during their disease course. Three patients were also treated with Chinese herbs and were able to stabilize their symptoms. Around half of the patients ultimately had a favorable outcome with immune suppressors, but around 15 percent did not respond well to this approach and complete remission was rare. Two of the patients ultimately died from complications.

About Myasthenia Gravis

Myasthenia gravis is a long term autoimmune disease that is most characterized by weakness of the skeletal muscles which can affect a patient’s ability to move and breathe. As an autoimmune disease, myasthenia gravis is ultimately the result of abnormal immune system behavior in which the system attacks normal body tissue. In this disease, the immune system produces antibodies that inhibit regular neuromuscular function. Symptoms of the illness include muscle weakness that worsens after activity and gets better after resting. This weakness may affect the face, eyes, neck, breathing, and limbs. It may cause speech and swallowing difficulties, eyelid drooping, shortness of breath, and blurred vision. In severe cases, patients may require breathing assistance with a ventilator. Treatment options for myasthenia gravis include immunosuppressive medications, thymus gland removal, IVIG, and plasmapheresis. Most patients can effectively manage the condition with treatment. To learn more about myasthenia gravis, click here.

Why Does it Matter?

While retrospective, natural history style studies may not really seem like huge research breakthroughs, they can nevertheless provide extremely valuable information, both for researchers and for patients. This study, for instance, highlights that people with this form of myasthenia gravis often see progression to generalized symptoms relatively rapidly. Additionally, the prevalence among women over age 50 is also not typical for myasthenia gravis is a whole, which can help doctors understand early on that the case could be Musk-positive.

The findings also revealed that a small number of patients did not respond well to common myasthenia gravis treatment approaches:

“The use of combination treatment might be helpful for symptom improvement and clinical outcome…however, some patients with MuSK [antibodies] responded poorly to standard care. Therefore, early introduction of more effective treatments should be considered once a diagnosis is confirmed.”

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