I am currently sero negative with positive SFemg, It is a nightmare to get treatment in my locality, and so I have learned to build my own care plan, due to neccesity. Be sure to keep good contact with your medical professional. Depending on your location, (I just saw your in Australia) your present Dr may very well be on board with sero-negative options otherwise have at least 1 medical professional on your 'team' who treats sero-negative patients. Be sure to build a supportive network of friends and family, as far as possible. I have finally been referred to 'find' a Doctor to start me on Mestinon. The US seems to offer a lot smoother medical options for sero negative patient, so hopefully you have similar level of care in Australia.
I have never heard of positive striated anti body, so maybe you could tell us more, when it's easy.

I am Seronegative as well & yes I responded well to treatment. After diagnosis my MG was able to be controlled by adding Mestinon & Lyrica. I was already on Cellcept for my other autoimmune diseases. But since the first heatwave of the summer we are throwing everything at my most recent flare. IVIG infusions every 2 weeks & I am also back on steroids for the foreseeable future until my symptoms subside. Fingers crossed. This summer has honestly sucked. The heat hit me hard.