Hi woodbegood, Primary as stated by your Doc, is disease of the thyroid gland itself. Secondary would be causes by other gland-(s) causing the thyroid to low-function, such as the pituitary gland (in brain), not being able to send ample amount of TSH, because it too has a problem, or other endocrine disorders like adrenal insufficiency, have been known to cause secondary thyroid disfunction.
If it was the radiation that dammaged your thyroid and only your Doc can actaully determine this, it would still be primary hypothyroidism because it caused a permanent problem in the gland itself.
Chemical Hypothyroidism, can be caused by medicines, chemicals etc... but many times resolves once that chemical is removed from a person's system.
If he says it's primary, that would be your thyroid and you will need hormone replacement most likely, permanently.
Hope that helped.
thanks for the insight-geesh! it's a wonder how ya figure anything thing out with this thyroid thing-i've been so confused since trying to learn-i don't even know which way to turn-i guess what i'm really wondering is has the interferon (that's the chemo i was on) totally destroyed my thyroid & will it continue to burn out? will it develop into something else? these are probably questions that can't don't have answers-just trying to figure out where i stand.