Hi, Interested. Welcome. You've gotten some great responses.
I have to say that if your son had a thymoma, an actual CANCER of the thymus gland, I would seek out a second opinion about the radiation or chemotherapy. Some cancers, once "opened up" and carved out, tend to spread. If even a little bit is leftover, which can be hard to determine, it can grow again.
Your son will need a lot of support from not only a neurologist but a pulmonologist. MG affects the breathing muscles and a pulmonologist is the specialist who can do pulmonary function tests and monitor any worsening of breathing. There are specific tests that look at muscle weakness called MIP (maximum inspiratory pressure) and MEP (maximum expiratory pressure). I cannot stress enough the importance of having a good pulmonologist.
I echo the concern about your son sounding like he is getting worse. He can't be shy about calling his neuro when that happens! There's no point in having any pride with MG. You can't "tough it out." MG can tank a person very quickly, sending them into an MG crisis.
An MG crisis is where you can't breathe well (in and/or out), swallow well or are generally more weak. At the point of being so weak, he needs to dial 911. EMT's can help someone in an MG exacerbation (an "almost" crisis) and a crisis until they get to the hospital.
A person with MG can also get weak so slowly that they don't realize how bad off they are. After some experience with MG, he will know to check things like his grip, arm strength, ability to take a breath in and out, etc. And he'll get to know when to rest. MG is usually managed with drugs but using common sense and alternating activity with rest/nap/sleep is essential to managing it.
There are things that can make MG worse. There are few places of worship I've been in that are cool enough. Extremes of heat and cold can make MG progressively worse. If there is no AC, then a well-placed fan will help. Infections, lack of sleep, a poor diet, stress, etc. can make MG worse.
There are drugs that can make MG worse too. Have you or your son been to www.myasthenia.org
for more information?
I certainly do not mean to offend you or your son by saying this but the only person who can really help your son is your son. He does have to come to terms with the unpredictable nature of MG. You can't "control" it and it has a mind of its own. And I'm glad the other person he knows can manage to give sermons but that does not mean your son will be able to. No, I'm not being pessimistic. It's just that MG is not the same for one person as it is for another. It'll take some time to figure out what he can do. And that can change over time.
I'm glad he got diagnosed and got some treatment. If he gets worse, like is seems as though he is now, he needs to get some more help. No one wants to admit they are getting worse but, with MG, you can't wait for help.
I hope he'll have a good life with MG.