I just want to say thank you for this, as my Autistic DD is currently going through a severe needle phobia phase after a bad experience. I think the medical community really need to take note of how much Autism affects individuals (especially children)
OP, I'd also like to say well done for how you've handled this so far. As an Autistic woman with an Autistic DD, I get sick of being called an Anxious Mum etc. We know our kids best.
The Troponin numbers going down is brilliant. Fingers crossed he's on the mend.
Just want to add one thing. DD and I both have Hypermobile EDS. It often presents alongside Autism. If undiagnosed, then it's possible to have unknown heart issues (I have tricuspid valve regurgitation, DD has mitral valve regurgitation and my sister had ventricular septal defects) All of these mean heart infections are more common.
I hope that the eventual MRI helps with your DS' full and proper diagnosis, treatment and also lead to a full recovery. My sister was entirely non verbal and we thought she just had flu. She had Endocarditis. You got your DS to hospital quickly, and that's the main thing. I'm sorry you very had conflicting advice and information from doctors. Never back down.
Much love to you, your DS and your DD. I have an ex who would be as much of a chocolate fireguard as yours, so my sympathies there also.