I am very hesistant to blame the thyroid disease as the cause for his delay, many many times we have no cause. You have had an extensive workup including imaging. If he was born with congenital hypothyroidism these kids truly have classic findings, large tongue, mental delay, called cretinism-I dislike that name, your child sounds like there are other vague developmental needs. It is hard to tell, if he was born in the US, then at birth they did a newborn screen and screened him for congenital hypothyroidism. I would focus on his overall needs, talk with his peds endo about his weight if that is now a concern, what genetic testing was done? did they test for prader willi syndrome? down syndrome?
rbcf
rbcf