Yes, Riley had this as a puppy. It was not diagnosed properly, because puppies don't normally get it. The first sign we missed was he was kind of uncoordinated. We thought he was a puppy and just maturing and needed to get stronger.
He would throw up a lot. Mostly in the car. I figured he was car sick. He sometimes threw up at home. We fed him with a raised bowl, because he was having pano issues with his front legs. That ended up helping the mega E that happens with the disease. We didn't know at the time though.
One day he looked stiff while walking after breakfast. By that night he could barley walk with his back legs. I told the vet at that visit that after he eats he sometimes makes this slight coughing noise and he had thrown up a large amount of white foam 2 weeks prior. (it was very scary). I guess the vet didn't put two and two together. ( I no longer go to that vet. I feel he put Riley through more than he needed to and it made things worse.) Xrays were taken, nothing abnormal was found. He was put on steroids and withing 3 to 4 days he was walking better. Then he threw up after breakfast. The white foam, but this time he was grinding his teeth and whining and making terrible noises. .....I can't relive it now. It's to upsetting. Here's the link for when it was happening.
Anyway, he had mega E so bad he couldn't keep anything down, pneumonia and he was suffering. At this point we had him down at a specialist vet. He was very grave with his prognosis. Basically if he could get over the pneumonia, he still was not able to keep anything down. If somehow we solved that issue (unlikely) he would continue to aspirate his food and water and continuously battle pneumonia all his life....not to mention the issues he would have with the Myasthenia Gravis.
I hope the Myasthenia Gravis was caught early in your dog. Riley was just to far gone and with it causing such severe Mega E he just did not have the odds in his favor. If love and money alone could have saved him he would still be here, but I could not let him suffer. I still miss him terrible.
I know my experience isn't very positive, but it doesn't normally happen in puppies. I read it can be treated.