I have resistance to thyroid hormone. Finally formally diagnosed last fall. I'm 49 and have had a lot of chance to research (since 1993) and have tons and tons of information and can answer almost anything you wanna know.
Along with the mri, they should also do a TSH alpha-subunit to completely rule out a TSHoma. Those are mighty rare. RTH isn't quite as rare but there's very few of us that have actually been diagnosed. I've only run across a few in my travels thru cyberspace and most of them are children. I know of one other adult but have not been able to speak with her.
I was diagnosed by the pediatricians as a hyperactive child and after attempts at tranquilizing me, they finally tranquilized my mom. But I really didn't have a lot of physical problems with it until I was 22 when it kinda slammed me. I've been on and off thyrotoxic ever since as everyone continued to scratch their heads at the normal TSH level. Started treatment this last may and although we're still in the adjustment period, I'm feeling a lot better.
I'd love to hear about what you've been thru, what your lab levels are and whatever. It gets kinda lonely here being the resident mutant.