Myasthenia gravis – causes, symptoms, treatment, pathology

Myasthenia gravis, is a Latin expression that
literally means “grave muscle weakness,” which perfectly describes the weakness that
happens when this autoimmune disease affects the skeletal muscles. People with myasthenia gravis might wake up
feeling fine, but get progressively weaker as the day goes on and by the end of the day
they might feel very weak, sometimes even getting weaker with repetitive movements like
chopping vegetables. Myasthenia gravis can affect the extraocular
muscles, which control movement of the eye as well as the eyelids, so individuals might
have diplopia or double vision, as well as ptosis, or drooping eyelids. Myasthenia gravis preferentially affects young
women in their 20s and 30s and older men in their 60s and 70s, but the cause of this odd
“bimodal” distribution of age-of-onset isn’t quite clear. To better understand myasthenia gravis, let’s
review normal muscle contraction but at the cellular level. First you’ve got your motor neurons that
release the neurotransmitter acetylcholine at the neuromuscular junction, which then
binds to nicotinic acetylcholine receptors on muscle cell membranes. Binding of acetylcholine to its receptor activates
a chain reaction in the muscle cell that ultimately results in muscle contraction. But what happens in myasthenia gravis though? Well remember that it’s an autoimmune disease,
specifically one that’s categorized as a type II hypersensitivity which causes cytotoxic
injury meaning that it results in the lysis or death of host cells, which is mediated
by autoantibodies, which are antibodies that are specific for our own cells or proteins. Alright, so in this case, the patient’s
B cells inappropriately make antibodies that bind to nicotinic acetylcholine receptors
on the muscle cells. Once acetylcholine receptors are bound by
the antibody, they are unable to bind to acetylcholine, and therefore don’t respond to the “contract”
signal from the central nervous system. Anti-acetylcholine receptor antibodies can
also activate the classical pathway of the complement. The complement system is a family of small
proteins that work in an enzymatic cascade to fight off bacterial infections. The activation of complement causes inflammation
and destruction of the muscle cells and reduces the amount of acetylcholine receptors on the
surface. Now a minority of people with myasthenia gravis
produce another type of harmful antibody called muscle specific receptor tyrosine kinase antibodies,
which attack proteins inside of muscle cells instead of nicotinic acetylcholine receptors
on the muscle cell surface, but they similarly leads to destruction of healthy cells. In very rare cases, myasthenia gravis can
present as a paraneoplastic syndrome, which means that an underlying cancer like bronchogenic
carcinoma or thymic neoplasm (also known as thymoma) generates an immune response which
results in generation of autoantibodies. In some cases, if certain muscles are affected,
myasthenic patients can experience a myasthenic crisis, which is a life-threatening manifestation
of the disease. An example of this might be a decreased function
of the muscles that control breathing. The good news is is that treatment has been
able to reduce mortality from myasthenia gravis. One type of medication is an acetylcholinesterase
inhibitor, like neostigmine or pyridostigmine. Acetylcholinesterase degrades acetylcholine,
so acetylcholinesterase inhibitors stop acetylcholinesterase from breaking down acetylcholine, which ends
up increasing the concentration of acetylcholine around muscle cells and helps counteract the
effects of acetylcholine receptor antibodies. Myasthenia gravis is also treated with immunosuppressive
drugs (like prednisone), which reduce the production of the harmful antibodies. Finally, a lot of people with myasthenia gravis
undergo surgical removal of the thymus. This seems to reduce the muscle weakness symptoms
even in people that don’t appear to have any identifiable problems with the thymus
gland itself. It’s possible that this is because helper
T cells, which originate in the thymus, help B cells make antibodies to the acetylcholine
receptor. Alright, as a quick review—myasthenia gravis
is a type II hypersensitivity disorder where the body produces antibodies that most commonly
target nicotinic acetylcholine receptors on the surface of muscle cells. The antibodies block the receptors which means
the signal to contract isn’t received. Those antibodies also activate the complement
pathway which leads to muscle cell destruction. Myasthenia gravis preferentially affects young
women or older men and commonly affects the extraocular muscles leading to eyelid drooping
or double vision, but it might affect any skeletal muscle. Thanks for watching, you can help support
us by donating on patreon, subscribing to our channel, or following us on social media.


  1. I've had Mg since 2009 check out my videos because I've used many different ways to help symptoms stay at bay.

  2. Osmosis is incredible. Almost all of my medical school class bought subscriptions and we've been using their built-in questions, plus student-generated questions, since block 1.

  3. I have myasthenia and I'm backwards I worse in the morning and better as the day goes on. Is there anyone in Victoria Australia that has this as I would like to know how u deal with it

  4. Hello I love your videos, you make learning fun but can I suggest a correction? Myasthenia is a Greek word not Latin from Greek "μυς" meaning muscle and "ασθένεια" meaning weakness. Thanks

  5. About the surgical removal of the thymus, is it done in kids or teens only? because from what I remember the thymus
    involutionates at a very young age and future t cells will be "born" out of older t cells.
    P.D: Sorry if I couldn't explain myself well, english is not my first language.
    Love your videos and drawings BTW <3

  6. Great video! There is also Seronegative MG (can be confirmed via SFEMG, Tensilon test) and 3 other antibodies that have been recently discovered- these include LRP-4, Agrin, and Cortactin.

  7. I really really love your video but I have a small irrelevant correction to make. Myasthenia is actually a greek word.

  8. I'll be having my thymectomy this Friday. I was diagnosed last January when I was in crisis state and being in the ICU for 2.5 weeks. After reading these comments, I'm happy to see I'm not alone.

  9. Was Dx with this disorder just over 2 years ago although by history have had it just over 25 years. I am male, 69 yrs of age and when I first started having "problems" in the military I was told that I was not conditioning properly. I worked hard to stay in the military until I was able to retire but continued to have episodes of sudden weakness and double vision. Recently I was admitted to hospital because I kept falling, could not get up. I was found to have URI, UTI with aggression of Myasthenia Gravis. Again, more PT, OT and god knows how many new medications. I also have COPD and asthma. Looking to try to get into an assisted living facility.

  10. wow amazing lucture ,,as a student you helped me man ,,can you tell me your name and your wepsite in google

  11. I have this disease,but i can't do any surgery because it only effect my eyelid and the doctor said that ever if i do the surgery they dont guarantee the surgery will success

  12. I am 63 years old and I have been suffering from the weakness periodically from the age of about 16. Every Time I went to a doctor all they wanted to test me for was MS. I was finally diagnosed 6 years ago. When I walked into the Neurologists office my first words to her were, "You are not testing me for MS I do not have MS I have been tested for it for the past 40 years and I don't have it" she told me " No you don't have MS but I do think I know what you do have." She did a neurological evaluation and then did some blood work and told me to come back in a 2 weeks. I was pretty sick at the time, but agreed. I went back and I was actually grey at the time. I was so weak I could barely walk even with the aid of my walker. She told me what I had was Myasthenia Gravis. She explained it to me in language I could understand, and told me I needed to be admitted right away. Well this was 2 days before Christmas and I had 35 people coming for Christmas dinner. I asked if it could wait till after the first of the year. She took one look at me and said you will not be alive at the first of the year, if you don't get treatment. I told her the situation I was in and we agreed I would go in right after Christmas. I was with my daughter in law and we had to stop and get a last minute gift for my grandson, I stayed at the front of the store because I felt so horrible. And to make it even worse people kept stopping and asking if I was okay and did I need an ambulance. Anyway she got the gift and I felt so bad I almost told her to take me back to the doctor so I could go to the hospital. By the time I got home all I could do was fall into a chair. I was beat, and in walks a friend ( one of my daughter in law's uncle's, who just happens to be a chief.) Any way he told me that was now his kitchen and if I wanted anything I was to tell one of my grandchildren and he would get it. Anyway Christmas went off great and I went into the hospital a couple of days later. Then came my first experience with plasmapheresis. I want to tell you, doctors need to know there is more out there then MS. I was beginning to think I was crazy, I even asked my primary care doctor to send me to a psychiatrist, because I had become convinced of it. After a couple of sessions, he revealed that I was not crazy and they symptoms were not in my head.

  13. Hi, my name is Phoebe and I have Myasthenia gravis I have problems at school and my ahnds het tired writing with a pencil and paper so this causes me to have a school ipad for me to type instead of writing. I was diagnosed at 8 years old in August and I am 9 almost 10 years old. For my treatment I do IVIG. Sometimes I tell people i have Myasthenia gravis and they are like what is that? Now i will say check out Osmosis video about it! Thank you for sharing more about this disease! -Phoebe

  14. Thank you! i have recently been diagnosed with MG, this video was helpful to share with family and friends

  15. I got it when I was 13. I’m 25 now. I take prednisone, pyridostigmine and I’ve had the thymus gland removal. For me my symptoms has become less and less frequent but it’s not completely gone

  16. I have congenital myasthenia which is kind of like this but I was born with it. From some research I’ve found that it’s very similar to this so this really helped me understand what I have just a bit more thanks 🙂

  17. This video is a wonderful example of why modern medicine is broken. There is no attempt to understand what causes the disease, nor to cure it. Instead, the symptoms are controlled with drugs. The video didn't even mention the central part played by vitamin D in the aetiology of the disease.

  18. I am just a little bit confused. In one of the Ted Talk questions it asked which age group and sex does the disease target. The correct answer was women over the age of 40. But as your video showed, it affects young women in their 20s-30s or older men in their 60s-70s. The answer doesn't seem to match up with what you have in your little presentation.

  19. I am 19 years old, and the symptoms showed when I was 7 or 8 years old, so how the fuck it occur to males above 60 years?

  20. I went to a new job today. Everyone else there was fine, before lunch I became so weak and painful that vomited from the pain. Ive never experienced anything like this. I recently went through 6 full weeks of Shingles and am getting a little concerned (okay alot concerned). I have other auto-immune disease as well, i.e. crohns, hashimotos to name a few.

  21. I really love your videos! You make it easier to grasp the whole concept of whatever topic you discuss in a few minutes!

  22. my brother have MG pray for him he is in the hospital in a bad condition and inmy country we dont have good medical care so pray for him please

  23. I ABSOLUTELY thought that drawing of the junctional folds in the synaptic cleft were microvilli/cilia and spent about an extra 40mins trying to figure that out, but otherwise great resource! Thank you for creating it!

  24. I was reading China Rich Girlfriend moments ago and read that one character there said that this condition sounds like mayonnaise athena gravy.

  25. Kürtlere villa verebilir belki. Ne abzürd soru be kardeşim. İstanbul'da yaşayan herkese yönelik hizmet yapılır. Bir belediyenin Kürt'e, laz'a, Çerkeze, Abaza'ya ayrı ayrı hizmetleri mi olurmuş?

Leave a Reply

(*) Required, Your email will not be published