It sounds as if the brain MRI will help point you in one direction or the other (MS or MG). Although for perspective, when I started experiencing restless legs, I researched and was able to confirm it can be a symptom of MG. The chest pain I've had ranges from flickering pains in muscles of the ribs and sternum, pain at the top point of inhalation, and eventual spread and intensity of pain to the point it felt my chest was being crushed. So I'm curious whether that's similar to the pain you've experienced or if it was more along the lines of the 'MS hug' which people describe as a boa constrictor squeezing band sensation.